Pecan Technology

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Pecan Technology

Pecan Technology Edited bU

Charles R. Sar\terre



© 1994 Springer Science+Business Media Dordrecht Originally published by Chapman & Hall in 1994 Softcover reprint of the hardcover 1st edition 1994

All rights reserved. No part of this book may be reprinted or reproduced or utilized in any form or by any electronic, mechanical or other means, now known or hereafter invented, including photocopying and recording, or by an information storage or retrieval system, without permission in writing from the publishers. Library of Congress Cataloging-in-Publication Data

Pecan technology / edited by Charles R. Santerre. p. cm. Includes bibliographical references and index. ISBN 978-1-4613-6011-7 ISBN 978-1-4615-2385-7 (eBook) DOl 10.1007/978-1-4615-2385-7 l. Pecan. 2. Pecan-Postharvest technology. 3. Pecan industry. SB401.P4P43 1994 338. 1'7452--dc20

British Library Cataloguing in Publication Data available

93-42091 CIP

DEDICATION To all those who have contributed to, or will contribute to, the success of the pecan industry.

Table of Contents

Foreword Jasper Guy Woodroof




List of Contributors

1. 2. 3. 4. 5. 6. 7. 8. 9.


An Overview of the Evolution of the U. S. Pecan Industry Bruce W. Wood, Jerry A. Payne and Larry J. Grauke Pecan Production Ray E. Worley Pecan Physiology and Composition Ray E. Worley Pecan Processing Charles R. Santerre Mechanization of Post-Harvest Pecan Processing Kevin A. Sims Microbiology and Sanitation Larry R. Beuchat Pecan Composition Charles R. Santerre Methods for Measurement of Pecan Quality Marilyn C. Erickson Structure and Performance of the Pecan Market Wojciech J. Florkowski and E. Eugene Hubbard

12 39

49 68

87 98

III 134

Appendix: Further Reading






Flavorwise and texturewise pecans are the "Queen of the Edible Nuts." This has been verified by salters, bakers, confectioners and ice cream manufacturers in America and western Europe. Hickory nuts and macadamia nuts are close behind, but are available only in limited supply. Pecans are among the nuts highest in oil content. In general, the varieties of nuts with the highest oil content are also rich in flavor and tender in texture. Some varieties of pecans (i.e., Schley and Curtis) have been shown to contain as much as 76% oil. The oil in pecans is highly unsaturated, which means it is desirable from a nutritional standpoint but that it is also highly susceptible to oxidation which can cause pecans to tum stale and rancid. Pecans used in confections, bakery goods, cereals, or in snacks are more subject to staleness and rancidity than most nuts because these products are often stored at ambient temperatures. For this reason, pecans are considered to be semi-perishable and are not used in some "fine" products due to their limited shelf-life. Research at the Georgia Experiment Station has shown that raw pecans or most pecan products may be held in good condition for more than 20 years if freezing is the mode of preservation. However, development of new products demands that pecans be stored at ambient temperatures for extended intervals. Pecan 'meat' is easily bruised during shelling and handling. Bruising ruptures the epidermal cell walls and releases free oil to the kernel surface where it is exposed to oxygen which can lead to oxidation and rancid flavor development. Therefore, pecans require careful handling and better packaging than many other nuts due to their chemical and physical nature. Roasting pecans during processing increases the rate of staleness and subsequent rancidification by at least four times by destroying the natural antioxidants or by releasing oxidizable lipids from stable compartments within the cells. For example, roasted pecan halves placed in clear bags and held at room temperature



From 1970 to the mid-1980s, the pecan industry has been rather static in growth when compared to other tree nuts, such as almonds. During this time frame, pecan production has increased 34% and consumption has increased 31 %, while almond production has increased 300% and consumption has increased 57%. * The real price (which adjusts for inflation) of pecans has dropped 50% while the real price of almonds has dropped 39% even though almond production grew almost ten-fold greater than did pecan production. One reason for the success ofthe almond industry has been market expansion due to aggressive promotion efforts both in domestic and foreign markets. Foreign sales of almonds have increased 220% while foreign sales of pecans have increased by only 10%. The pecan industry must use a similar approach to market expansion as implemented by the almond industry. Furthermore, technological advances are necessary to reduce or eliminate problems associated with using pecans in food products (i.e., limited shelf-life, contamination by weevil-larvae or shell-fragments, and adverse interactions between pecans and other components in food products). This book discusses many factors which influence pecan quality from growth in the orchard, to harvest, and through processing. Extensive information is presented regarding variety, cultural conditions, mechanization, processing, storage, prevention of spoilage, and methods for evaluating the quality of pecans. In addition, information will be presented from surveys of growers and processors to determine a relationship between price paid for pecans and pecan quality. Acknowledgments

The editor expresses appreciation to Ms. Jeanine Kee for her assistance in preparing this book. *Mizelle, W. O. 1989. Tree nuts: Production, prices, consumption and foreign trade. University of Georgia Cooperative Extension Service. Miscellaneous Publication No. 328:1-20.


List of Contributors

Larry R. Beuchat, Ph.D. Food Scientist Department of Food Science and Technology Georgia Station University of Georgia Griffin, GA 30223

E. Eugene Hubbard Agricultural Economist Department of Agricultural Economics Georgia Station University of Georgia Griffin, GA 30223 Jerry A. Payne, Ph.D. Entomologist USDA-ARS Southeastern Fruit and Tree Nut Laboratory Byron, GA 31008

Marilyn C. Erickson, Ph.D. Food Scientist Department of Food Science and Technology Georgia Station University of Georgia Griffin, GA 30223

Charles R. Santerre, Ph.D. Food Scientist Department of Food Science and Technology University of Georgia Athens, GA 30602-7610

Wojciech J. F1orkowski, Ph.D. Agricultural Economist Department of Agricultural Economics Georgia Station University of Georgia Griffin, GA 30223

Kevin A. Sims, Ph.D. Food Scientist Department of Food Science and Technology University of Georgia Athens, GA 30602-7610

Larry J. Grauke, Ph.D. Horticulturist USDA-ARS Pecan Research Laboratory Somerville, TX 77879


xiv / Contributors

Bruce W. Wood, Ph.D. Horticulturist USDA-ARS Southeastern Fruit and Tree Nut Laboratory Byron, GA 31008 Ray E. Worley, Ph.D. Horticulturist Department of Horticulture Coastal Plain Experiment Station University of Georgia Tifton, GA 31793-0748

Jasper Guy Woodroof, Ph.D. Food Scientist Department of Food Science and Technology Georgia Station University of Georgia Griffin, GA 30223

1 An Overview of the Evolution of the U. S. Pecan Industry Bruce W. Wood, Jerry A. Payne and Larry J. Grauke

Introduction Pecan [Carya illinoinensis (Wangenh.) K. Koch], preferably pronounced as pi'kiln over pi-'kan or 'pe-,kan (Llewellyn 1985), is one of the few native North American plant species that has been developed into a significant agricultural crop. It has also become one of the few indigenous u.s. food crops that is commercially cultivated outside the u.s. (i.e., Mexico, Australia, South Africa, Israel, Brazil, Argentina, Egypt, etc.). As perhaps the economically most significant native contributor to the U. S. agricultural economy, wholesale revenues approximate $200 million annually (USDA 1991) and approaches $400 million when all aspects of the industry are included (Crocker 1989). Pecan could be considered to be relatively unique in that it is one of the few food crops in which a relatively detailed record exists concerning its cultivation and spread as an agricultural commodity. The history of pecan husbandry therefore provides a unique glimpse, or case history, of this process and may potentially contribute valuable insight into understanding the initial domestication processes of more ancient crops and may aid in the domestication efforts of species that currently exist in the wild state. Domestication is a rather general term possessing broad-sense (being somewhat adapted to life in intimate association with and to the advantage of man) and narrow-sense (being sufficiently adapted so as to be devoid of significant deficiencies in relation to the traits judged by man to be important) subdivisions. In the botanical or evolutionary sense, pecan would be classified as relatively 'undomesticated' because the cultivated genotypes are only slightly diverged from that of the wild type and would therefore be expected to possess the fitness necessary for survival in its natural environment. As compared to many crops, man has done a somewhat better job adapting his horticultural skills to meet the constraints of pecan germplasm than he has of altering C. R. Santerre (ed.), Pecan Technology © Chapman & Hall, Inc. 1994


2 / Bruce W. Wood. Jerry A. Payne and Larry J. Grauke

the germplasm so as to produce a 'botanically domesticated' crop. However, this semi-wild or somewhat crudely domesticated state of cultivated germplasm has not prevented the development and growth of a major industry. While the factors contributing to this growth were many, there were salient events and advances that made this evolutionary-like process possible. The objective of this introduction is to present a brief overview of pecan as a horticultural crop possessing a unique North American heritage, to briefly describe primary factors leading to the growth of the U. S. pecan industry and to provide an overview of the current nature of the U. S. industry. Factors Propelling the Growth of the Pecan Industry

Factors and events molding the evolutionary-like changes relevant to the U.S. pecan industry are myriad, subject to one's perspective, and their relative importance is debatable. According to our general opinion, the following factors can be considered to be important circumstances/events that have elevated pecan husbandry to today's status. Quality Product

Interest in pecan appears to have originated with the arrival of the aboriginal inhabitants of the Western Hemisphere to the major river systems of central and eastern North America (and possibly northeastern Mexico). Since pecan was readily accessible to waterways, and was generally regarded as among the best tasting and easiest to shell of the 14 hickory (Carya spp.) species native to North America (Stone 1962), it was heavily utilized and highly desired by precolonial residents. Its native habitat is the floodplains along the Mississippi, Ohio, Missouri, the Red Rivers and their tributaries, and along many of the largest rivers of central Texas and northeastern Mexico. During this era, the range of pecan appears to have extended from about 42°20' North latitude in the north (Bellevue, Iowa) to that of about 16°30' (Oaxaca, Mexico) in the South; however, the origin of the isolated pockets of pecans throughout most of Mexico is still being evaluated as to whether they were of natural or human origin. The wide natural range and abundance of pecan led many Indian tribes inhabiting the U.S. and Mexico to utilize the wild pecan as a prized and major food source during the autumn (Baskett 1906). One utilization of kernels was to produce a "cream-like" fluid that was used for cooking and drinking (Stuckey and Kyle 1925); it also is alleged to have been utilized by some Indians to produce a fermented intoxicating drink termed 'Powcohicora' (from which the name "hickory" was derived), which made the braves 'braver' (G. Taylor, personal communication; Strachey 1612). Undoubtedly, this use also contributed to the nuts' popularity among the aboriginal inhabitants. In fact, the name, "pecan," is an American Indian word of Algonquian origin that was used to

An Overview of the Evolution of the U.S. Pecan Industry / 3

designate "all nuts requiring a stone to crack" (TrumballI872 as cited by Stuckey and Kyle 1925); however, it was also a Natchez Indian word specific for the plant we now know as pecan (McHatton 1957). It was a major food and trade item among American Indians (Celiz 1935); in fact, there is evidence that they cultivated the tree. Creek Indians were reported to have possessed 'ancient cultivated fields' of hickory (presumably pecan) (True 1917). One of the first known cultivated plantings appear to have been by Spanish colonists and Franciscans in northern Mexico in the late 1600s or early 1700s (Onderdonk 1909; Woodruff 1967). These Mexican plantings are documented to about 1711, predating by about 70 years the earliest recorded planting by colonists in the U.S. The earliest known planting in what is now the U.S. was at Long Island, NY in 1772 (McHatton 1957). Nuts from the northern portion of the range reached the English speaking area of the Atlantic Seaboard in the later 1700s and were commonly planted in the gardens of notable easterners such as George Washington (1775) and Thomas Jefferson (1779) (True 1917). During this time, settlers were also widely planting pecans in the gardens of communities along the Gulf Coast (Flack 1970). The economic potential of pecan had begun to be realized by the late 1700s, especially by the French and Spanish colonists settling along the Gulf of Mexico. By 1802, pecan nuts gathered from wild trees had already become an article of commerce in the Mississippi Valley and were being exported by the French to the West Indies. Presumably, the nuts were exported to the West Indies and Spain much earlier by the Spanish colonists in northern Mexico. Pecan's potential for cultivation was just beginning to be realized during this era. For example, it was advertised in London in 1805 that pecan was" ... a tree meriting attention as a cultivated crop" (McHatton 1957) and it was assumed that the success of cultivation attempts would hinge upon the responsiveness of pecan to clonal propagation techniques available at that time. However, it's innate recalcitrance to clonal propagation may have delayed its cultivation for several decades. Market

Prerequisite to the development of any crop is market demand and proximity. As a large port city, near the mouth of the Mississippi River, New Orleans was of great importance regarding the marketing of pecan (Flack 1970). Since the Mississippi River, its tributaries, and east Texas rivers encompassed much of the natural wild pecan population, there was the availability of an abundant supply of the highly desirable wild nuts in close proximity to this large population center and port city. The city therefore provided a natural market and avenue for the redistribution of nuts to other parts of the U. S. and the world. This market potential fueled considerable local interest regarding the planting of orchards. This interest in tum stimulated an adaptation of vegetative propagation techniques

4 / Bruce W. Wood, Jerry A. Payne and Larry J. Grauke

and led to the demand for grafted trees and for trees producing superior nuts. By the end of the nineteenth century, at least 15 commercial cultivars had been developed in the general region of Louisiana (Flack 1970). A second market of substantial importance was San Antonio in eastern Texas where it is reported that in some years the wild pecan crop harvested by farmers was more valuable than row crops such as cotton. As in Louisiana, the demand for pecans in south central Texas also stimulated considerable interest in the development of pecan cultivars during the late nineteenth century (McHatton 1959; and T. Thompson, personal communication). Vegetative Propagation

The American colonists had begun to acquire an understanding of the economic potential of pecan during the 1700s and early 18oos; therefore, pecan nuts had become an item of commerce and a small industry had been born. Interest in cultivating pecan proliferated at about the time that a solution was found relating to the wide variability in nut quality and quantity. Since pecan groves (a collection of trees established by natural forces) and orchards (plantings established by man) consisted of wild germplasm of diverse genotypes, plantings exhibited tremendous variability in nut size, shape, shell characteristics, flavor, fruiting age, and ripening date. While these variables may have presented obstacles to commercial cultivation and thus limiting the commercial value of pecans, it is perhaps the experience of cracking and shelling native pecans that created a premium market for large, thin-shelled pecans. This substantial variability among trees resulted in the occasional discovery of a wild tree with unusually large thin-shelled nuts. Nuts from such trees were especially valued and in high demand by consumers, and were recognized as a key to making money with pecans (Crane, Reed and Wood 1937). While it was recognized by the early 1800s that the establishment of grafted orchards would solve problems with variability and nut size and shelling characteristics, there had not yet been a successful adaptation of vegetative propagation techniques already known to be successful on certain other woody crops. However, in 1822, Abner Landrum of South Carolina published that he had developed a highly successful pecan budding technique. This discovery provided, for the first time, the opportunity to establish grafting plantings derived from superior wild selections rather than the diverse heterogeneous plantings utilized up to that time. This development, in tum, created an opportunity to avoid the many cultural and marketing liabilities common to heterogeneous planting. Unfortunately, this breakthrough was either lost or neglected and was not utilized again until the 1880s. It was not until 1846 that the vegetative propagation of pecan began to be utilized. In 1846 a slave gardener, named Antoine, of the Oak Alley Plantation (owned by Governor Telesphore J. Roman) in Louisiana, successfully propagated pecan by grafting a superior wild pecan (found by Dr. A.E. Colomb) to seedling

An Overview of the Evolution of the U.S. Pecan Industry / 5

pecan stocks (Stuckey and Kyle 1925). This clone was eventually named 'Centennial' because it won the "best pecan exhibited" at the Philadelphia Centennial Exposition in 1876. This planting, of what was to become 126'Centennial' trees, became the first known commercial grafted pecan orchard and appears to have been the first planting of relatively improved pecans. The successful adaptation of grafting techniques eventually led to the establishment of grafted orchards of superior genotypes and was a critical milestone in attempts to utilize pecan as a cultivated crop (Bailey 1922). Although a major technical breakthrough in pecan culture, these propagation techniques developed by Antoine were slow to be adopted by others and had little commercial impact until the 1880s when nurserymen in Louisiana and Texas learned of pecan grafting and began clonal propagation on a commercial scale. Gulf Coast Freeze

Another factor that accelerated cultivation was the destruction of citrus orchards along the Gulf of Mexico. Devastating freezes hit in the winters of 1886-87 and again in the winters of 1894-96, resulting in a generalized decimation of citrus orchards. In an attempt to find an alternative crop, much ofthis land was replanted with pecan, thus providing a demand for nursery stock in portions of the coastal region (Flack 1970). In addition to the initial intense interest around New Orleans, interest in pecan cultivation has spread to four other regions during the late 1800s, all of which were either on the fringe of the natural range or outside of it. These regions were southern Mississippi, northern Florida, southern Georgia and the upper Colorado River of central Texas (Flack 1970). The relatively concurrent events of the severe freezes and the introduction of clonal trees resulted in a substantial demand for the superior nursery-produced trees. Commercial nurseries soon followed in Florida, Georgia, Mississippi and Texas. This demand for nursery stock led to trees becoming very expensive ($2.50 per plant during the 1880s) and difficult to obtain; therefore, most pecan plantings established between 1870 and 1900 were by utilizing open-pollinated seed (even though most people apparently recognized that pecans probably did not come absolutely true from seed). These seedling orchards, many being several hundred hectares, were widely planted throughout the central and southern states, especially in areas bordering the Gulf of Mexico. The inadequate supply of improved trees began to be alleviated in the 1890s when E.E. Risien of San Saba, Texas successfully adapted a ring budding technique popularizing the potential for this technique and therefore vastly enhancing the grower's ability to obtain superior genetic materials. The result was a decline in the price of nursery stock and the introduction of clonal cultivars originating from superior wild trees. Such cultivars were 'Stuart,' 'Van Deman,' 'San Saba,' 'Moneymaker,' 'Columbia' (or

6 / Bruce W. Wood, Jerry A. Payne and Larry J. Grauke

'Rome'), 'Delmas,' 'Frotscher,' 'Kennedy,' 'Schley,' etc.; several of these are commonly found in contemporary commercial orchards. Seedling Selections and Breeding Efforts Another factor having major significance for the utilization of pecan was the interest exhibited by several growers in southern Mississippi (Jackson County, which was outside the native range of pecan) and central Texas. Several seedling orchards and nurseries were started from 1874 to about 1900. Early growers observed occasional seedling trees that bore large thin-shelled (commonly termed papershells) nuts. Such trees were clonally propagated and sold throughout the states bordering the Gulf of Mexico as interest in pecan increased. Out of this area came the cultivars that dominated orchard plantings throughout most of the next century. Even today, many cultivars developed in Jackson County, Mississippi (KenKnight 1970) and in central Texas (Burkett 1932) are considered to be the standards of the industry. Such cultivars as 'Stuart,' 'Desirable,' 'Western,' and 'Schley' continue to be the major cultivars produced in the industry with 'Stuart', 'Desirable', and 'Western' still being highly recommended for new plantings (Thompson 1990). One grower, a Mr. Forkert, became the earliest known pecan breeder (1903) and consequently produced several good cultivars (Crane, Reed and Wood 1937; Risien 1904). One of these was 'Desirable,' which may currently be considered to be one of the best cultivars for commercial cultivation in the southeastern U.S. environment. Similarly, E.E. Risien, a grower from San Saba, Texas, began breeding in 1904 and eventually produced 'Western Schley' (a standard of the western sector of the U.S. pecan belt). He eventually produced numerous cultivars and was a major factor in the popularization of pecan in Texas and the western U.S. (Crane, Reed and Wood 1937). Era of Speculation The era of the 1890s to 1930s was a time when many existing seedling orchards and groves were top-worked to establish improved cultivars (large and easy to shell nuts became the predominant criteria for improvement). The vast majority of these scion cultivars were from someone's favorite wild tree. The owners frequently gave the clone his surname or his wife's name and attempted to market clones with what would later prove to be an insufficient regard for proven horticultural characteristics. This practice resulted in the introduction of several hundred named cultivars (Crane, Reed and Wood 1937). During this era there was also an extensive proliferation of orchards in southwestern Georgia (an area well outside the species' native range) and in east central Texas. This proliferation appears to have been due to a spirit of speCUlation that began about 1900 and arose as a result of: (a) low land prices due to problems with cropping cotton; (b) exaggerated reports of wealth from cropping pecan; and (c) in the case of

An Overview of the Evolution of the U.S. Pecan Industry / 7

Georgia, an abundance of northern retirees believing sales propaganda which advocated a comfortable retirement from the revenue produced from a few hectares of pecans (McHatton 1957; Stuckey and Kyle 1925). The result was a speculative fervor and flurry of get-rich-quick schemes in which orchards were planted and quickly sold with a promise of wealth to the new owner. Thousands of acres were planted with the purpose of making money through selling orchards rather than through selling the crop. Since there appears to have been frequent misrepresentations of facts and a deficiency of adequate horticultural, pathological, and entomological information, this speculative fervor soon resulted in many unproductive orchards and a subsequent initial decline in the popularity of the crop. Because of this period of speculation, there was a major change in the nature of the evolving industry. The former region of major production had been Texas and Louisiana (native nuts) and southern Mississippi (seedlings); however, major production potential was now established in southwest Georgia [Georgia currently accounts for about 43% of the total U.S. pecan production and about 37% of the production from cultivars (USDA 1991)]. Many of these hastily established orchards in the southeast rapidly became unprofitable and were temporarily abandoned because of an inability of growers to control pecan rosette (induced by zinc deficiency). Chemicals

The recovery of the industry from the nutrition-related disappointments of the 1920s and 30s was largely due to the discovery that pecan rosette could be corrected by fertilization with zinc (Sparks 1987). This breakthrough stimulated great interest in renewing cultivation of abandoned orchards and the planting of new ones. While new trees continued to be planted between 1935 and the 1960s, the intensity of activity was far less than during the first quarter of the twentieth century. The chemical control of insect pests, such as hickory shuckworm, pecan weevil, aphids, pecan nut casebearer, etc. have also made a major contribution in allowing for industry expansion, especially with the availability of air-blast spray equipment that allow for rapid and economical control of insect and disease pests. These nutritional and pesticide related advances resulted with considerable emphasis being placed on reviving and invigorating previously established but abandoned orchards. The increase in pecan production in Georgia from 1970 to 1983 is reported to be "associated with the onset of widespread spraying to control insects and diseases and progress in correction of nitrogen, potassium, magnesium, and zinc shortages" (Sparks 1983). Sparks (1983) also indicates that a further "increase was associated with extensive use of irrigation, generally good sunlight conditions, and the additive efforts of these factors when combined with insect and disease control and improved nutrition." These improvements in cultural and management strategies had the end effect of retaining leaves in a relatively high

8 I Bruce W. Wood, Jerry A. Payne and Larry J. Grauke

state of efficiency; hence, maximizing assimilate accumulation and a subsequent moderation of alternate bearing and on enhancement of yield. Our experience supports this observation for not only Georgia but also for the southeastern section of the U.S. pecan belt (Wood 1989; Wood, Tedders and Reilly 1989). Improved Cultivars

This most recent growth phase of the pecan industry began in the late 1960s and spans to the early 1980s. During this era, additional hectares of pecan orchards were not only established in the traditional pecan growing areas, but were also established in the arid West, far removed from the natural range of the species. Many thousands of hectares of trees (mostly 'Western Schley' and 'Witchita') were planted in western Texas, New Mexico, Arizona, and California, thus extending the commercial pecan belt across the entire southern U.S. from North Carolina to California. This expansion was primarily due to the recognition that the demand for pecans had not yet been satisfied. The availability of highly precocious and prolific new cultivars from the USDA-ARS pecan breeding program (due to the breeding, evaluation, and promotion efforts of Louis Romberg and George Madden) appears to have also stimulated interest. Production from these relatively young trees and an increase in production from existing mature trees has been a major factor in catapulting pecan production and economic worth to today's relatively high level and has elevated pecan to that of being a valuable and unique contributor to the U.S. economy. U.S. pecan production has grown rapidly during the last 100 years, with initial production being predominantly seedling nuts produced from native or seedling trees until about 1958 when production from cultivars equaled that of seedlings (Figure 1.1). Production of nuts marketed from cultivars is continuing to rise whereas those from seedlings have been slowly dropping since 1963 (USDA 1991). Three-fourths of total commercial production is from the five states of Georgia (43%), Texas (24%), New Mexico (13%), Arizona (10%) and Louisiana (7%). The bulk of improved cultivars are primarily produced from Georgia (37%), Texas (14%), New Mexico (13%) and Arizona (10%), respectively (Table 1.1). While the U.S. pecan industry has evolved to a level of economic significance, in the mid 1980s it encountered a substantial barrier to its continued growth. This barrier was a 'cost-price squeeze' that forced many growers and shellers out of business. The squeeze was primarily due to a historical failure of the industry to act in a concerted group effort to develop and expand markets; hence, there was a relative excess of nuts available for marketing, resulting in low wholesale prices. While the industry has now begun to address these marketing problems, it now faces a new and unexpected challenge of insufficient production of quality nuts and may experience problems retaining markets. This decline in production during the late 1980s and early 1990s is largely a result of production

An Overview of the Evolution of the U.S. Pecan Industry / 9 120~-----------------------,












c: 0

+: (.) :::::J




0 1910





75 Seedlings


.c: 0



oS 25

o~~~~~~~~~~~~~~~ '90 1910 '30 '70 '50

Year Figure 1.1. Time trend for the production of 'cultivars,' 'seedling' in-shell pecan nuts in the U. s.

declines in the southeastern U. S. and appears to be associated with a variety of biotic and abiotic stresses. The result is a decline in the availability of high quality nuts and an excess of poor quality nuts. While an increased and dependable supply of high quality nuts is needed by the industry, a diversion of lesser quality nut meats and pieces into new products is also needed by the U. S. industry.

10 / Bruce W. Wood, Jerry A. Payne and Larry J. Grauke Table 1.1. Average commercial in-shell U.S. pecan production by major producing states. Production is for the period from 1986-1991. The six-year period covers three alternate bearing cycles, hence giving representative comparisons: In-shell pecan production in millions of kg Cultivars




State b







Alabama Arizona Arkansas California Florida Georgia Louisiana Mississippi New Mexico North Carolina Oklahoma South Carolina Texas

3.5 9.6 0.4 1.0 1.4 36.7 1.4 2.1 12.7 0.6 0.6 0.9 13.5

4.2 11.4 0.5 1.2 1.6 43.5 1.6 2.5 15.1 0.7 0.7 l.l 16.0

2.6 0.0 0.3 0.0 l.l 6.4 6.7 1.2 0.0 0.5 5.6 0.6 10.1

7.4 0.0 0.7 0.0 3.0 18.1 19.0 3.4 0.0

6.1 9.6 0.6 1.0 2.4 43.1 6.7 3.3 12.7 l.l 6.2 1.5 23.6

5.1 8.1 0.5 0.8 2.0 36.1 5.6 2.7 10.7 1.0 5.2 1.3 19.8





16.0 1.7 29.0


aProduction data from 1991 V.S.D.A. Agricultural Handbook on "Agricultural Statistics". Data on Arizona are an estimate provided by the Cooperative Extension Service. "These are the primary commercial states. There is also limited commercial production in Missouri, Kentucky, Kansas, Illinois, Tennessee, Virginia, and Iowa. C.Cultivars' means nuts identifiable as a particular quality cultivar when sold. d'Seedlings' consist of nuts from ungrafted trees, nuts from seedling or native groves and cultivars not identifiable as a cultivar when sold. e

% of national total of 'cultivar' nuts.

f% of national total of 'seedling' nuts. g% of total V.S. production.

References Bailey, L.H. 1922. Pecan. In The Standard Cyclopedia of Horticulture, pp. 2513-2517. Vol. 5. New York: Macmillian. Baskett, J .N. 1906. A study of route of Cabeza de Vaca. Texas State His. Assoc. Quart. 1(10):246-279. Burkett, J .H. 1932. The pecan in Texas. Texas Dept. of Agric. Bull. No. Ill. Celiz, F.F. 1935. In Diary of the Alarcon Expedition into Texas, 1718-1719. Trans. by Fritz Leo Hoffman, Quivira Soc. PubIs. 5:43-124. Crane, H.L., C.A. Reed and M.N. Wood. 1937. Nut breeding. USDA, Yearbook No. 1590, p. 827-890.

An Overview of the Evolution of the U.S. Pecan Industry / I I Crocker, J. 1989. Pecan promotion research act, In J. Crocker, ed. The Pecan Grower. pp. 1-3. Vol. 1. Flack, J.R. 1970. The spread and domestication of the pecan in the United States. Ph.D. Dissertation. University of Wisconsin, Madison. (unpublished) Llewellyn, W.A. 1985. Webster's Ninth New Collegiate Dictionary. Springfield, Massachusetts: Merriam-Webster Inc. KenKnight, G. 1970. Pecan varieties "happen" in Jackson County, Mississippi. Pecan Quarterly 4(3):6-7. McHatton, T.H. 1957. The history, distribution and naming of the pecan. 50th Proc. Southeastern Pecan Growers Assoc. p. 10-34. Onderdonk, G. 1909. Pomological Possibilities of Texas. Texas Dept. of Agr. Bull. 9. Risien, E.E. 1904. Pecan Culture for Western Texas. Published by the Author. Sparks, D. 1983. Alternate fruit bearing in nut trees. Ann. Rept. Northern Nut Growers Assoc. 74:197-230. Sparks, D. 1987. Apparent effect of zinc treatment on the growth rate of pecan production and yield. HortScience 22:899-901. Stone, D.E. 1962. Affinities of a Mexican endemic, Carya palmeri, with American and Asian hickories. Amer. J. Bot. 49:199-212. Strachey, W. 1612. The Historie of Travell into Virginia Britania, Glasgow: University Press. Stuckey, H.P. and E.J. Kyle. 1925. Pecan growing. New York: Macmillan. Thompson, T. 1990. Pecan cultivars: current use and recommendations. Pecan South 24(1): 12-20. True, R.H. 1917. Notes on the early history of the pecan in America. Ann. Rept. Smithsonian Institution, p. 435-448. U .S. Department of Agriculture. 1991. Agricultural Statistics. U. S. Government Printing Office, Washington, D.C. Wood, B.W. 1989. Pecan production resopnds to root carbohydrates and rootstock. J. Amer. Soc. Hort. Sci. 114(2):223-228. Wood, B.W., W.L. Tedders and C.C. Reilly. 1988. Sooty mold fungus on pecan foliage suppresses light penetration and net photosynthesis. HortScience 23(5):851-853. Woodroof, J.G. 1967. Pecan history and distribution. In Tree Nuts: Production, Processing, Products, pp. 1-38; Vol. 2. Westport, Conn: AVI

2 Pecan Production Ray E. Worley

Varieties Pecan varieties are marketed as native and seedling nuts or as improved varieties (Demena 1991). Native and seedling nuts are harvested from trees that have not been grafted or budded and do not have a variety name. Improved varieties (cultivars) are produced on trees that have been grafted or budded to a named variety. The quality and storage characteristics of nuts from each of these categories varies greatly. The nut characteristics of the native or seedling vary greatly due to different genetics for each tree. On the average, however, native and seedling nuts are small, difficult to shell, and have a low percentage kernel due to a thick shell. Native or seedling nuts usually have excellent flavor due in part to a high oil content, and are frequently preferred by many users. They are excellent for use in pastry and candy, but the small size and shelling difficulty preclude widespread use of native and seedling nuts for in-shell use. Price received by growers for native and seedling nuts is usually much lower than that received for better, improved varieties. Improved varieties are selections made from seedlings or controlled crosses that demonstrated desirable characteristics. These varieties have been propagated by budding or grafting onto selected rootstocks. Each tree of a named variety thus has the same genotype above ground but the rootstock is of unknown genotype. Nuts from all 'Stuart' trees are the same except for the influence of the environment and rootstock on yield and nut quality. Amateur pecan breeders released varieties such as 'Desirable,' 'Dependable,' 'Forkert,' 'Gratex' and 'Mahan-Stuart. ' Few varieties have been released from formal breeding programs other than those released by the USDA's W.R. Poage Pecan Field Station, at Brownwood and Sommerville, Texas. 'Barton' was the first release from the C. R. Santerre (ed.), Pecan Technology © Chapman & Hall, Inc. 1994


Pecan Production / 13

Figure 2.1. Pilcher)

'Oconee,' a newly released cultivar which shows promise. (Photo by Herb

USDA Breeding Program. Later, variety releases from this breeding program were given names of American Indian tribes. Varieties such as 'Wichita,' 'Choctaw,' 'Cheyenne,' 'Mohawk,' 'Kiowa,' 'Caddo,' 'Sioux,' 'Shawnee,' 'Shoshoni' and 'Tejas' from this program are recommended for Texas (Menges 1985), but most of these varieties are not well adapted to the southeastern U.S. One limitation of most of these varieties relates to lack of disease resistance in humid regions. 'Oconee' (Figure 2.1), released in 1990, has shown excellent yield, shelling, size, disease resistance and kernel quality characteristics in Georgia through 12 years of age and may be satisfactory for the southeastern U. S. (Worley 1991). Pecan varieties must have sufficient scab resistance in order for the disease to be controlled with existing fungicides and to perform satisfactorily in humid climates. A good pecan variety produces large, well-filled nuts with plump, bright, golden colored kernels, free of defects such as adhering hull, discolored veins, trapped packing material in grooves and kernel spots. Kernels should be slow to darken and slow to become rancid during storage. Traditionally, in-shell pecans are used during the Thanksgiving and Christmas holiday seasons. Early harvest is required to supply nuts to the distribution channels for the holiday market. Nuts of late maturing varieties are usually used by shellers. Early maturing varieties thus usually bring higher prices than later

14 / Ray E. Worley Table 2.1. Nut characteristics for selected pecan varieties grown at the University of Georgia Coastal Plain Experiment Station, Tifton, Ga. Variety



'Stuart' 'Desirable' 'Schley' 'Western Schley' 'Gloria Grande' 'Cape Fear' 'Sumner' 'Elliott' 'Wichita' 'Curtis' 'Maramek' 'Woodard' 'Moneymaker' 'Frotscher'

55 48 71 71 47 55 53

25 22 32 32 21 25 24 35 26 41 22 27 31 29


57 91 49 60

68 64

Percent Kernel

Shell Thickness

Maturity Date

46 51 56 54

Medium Medium Thin Thin Medium Medium Thin Thick Thin Thin Medium Very thin Thick Thin

Midseason Midseason Midseason Early Midseason Midseason Late Early Midseason Late Midseason Late Early Mid-late


53 52 51 58 54 55 55 44


maturing ones. Prices are a function of supply and demand and sometimes, as in 1990 when the supply of nuts was low, prices are higher later in the season. The advantage of early maturing nuts would be lessened if in-shell pecans could be sold as a "year-around" item instead of a "holiday-season-only" item. Pecan maturity dates range from the very early maturing varieties such as 'Starking Hardy Giant' and the newly released variety 'Osage' (Thompson 1990), which can be harvested in southern Georgia in early September, to very late maturing varieties such as 'Hastings' and 'Curtis' which mature in November. Some other early maturing varieties are: 'Candy,' 'Moneymaker,' 'Pawnee' and 'Shoshoni.' The organoleptic quality of a variety apparently has little relationship to maturity date. There are over 1000 named pecan varieties. The book, Pecan Cultivars Past and Present (Thompson and Young 1985) documents 1012 of them. Excellent color photographs of nuts, kernels, and trees of several of the older varieties are found in Pecan Production in the Southeast (Goff, Worley and Hagler 1989). Only a few of these varieties are of sufficient quality and are produced in sufficient quantity to be of commercial importance today. The varieties listed below represent a cross section of those currently grown and probably account for 75% of the world's production. Table 2.1 lists the nuts/unit weight, percentage kernel, shell thickness and nut maturity date for these varieties from data collected from variety trials at the University of Georgia Coastal Plain Experiment Station in Tifton, GA. Stuart

Probably more 'Stuart' nuts (Figure 2.2) are produced than any other variety. 'Stuart' is one of the oldest (1886) and most dependable varieties propagated

Pecan Production / 15

Figure 2.2.

'Stuart' pecans photo by Herb Pilcher.

(Sparks 1977; Worley 1983). It has medium size and medium shell thickness with fair cracking characteristics. Average annual yield over 69 years at the University of Georgia Coastal Plain Experiment Station was 71 lbs/tree (33 kg/ tree) which is 153% of its nearest rival, 'Moneymaker.' 'Stuart' averaged 147 lbs/tree (66 kg/tree) for the period of 1969 through 1989. Nut length is slightly longer than width, giving the nut a cylindrical shape with a blunt apex and rounded base. 'Stuart' has a midseason harvest date. 'Stuart's' scab resistance has made it an extremely popular cultivar for the southeast especially for plantings made prior to the development of fungicides and sprayers to deliver them. Strains of the scab fungus have evolved which now attack 'Stuart.' Although 'Stuart's' size, percentage kernel, and kernel quality are not the best, its popularity and consistency of production make it one of the most profitable nuts for commercial production. 'Stuart' is used widely for both in-shell and shelled pecan trade. One serious problem with 'Stuart' is lack of tree precocity. Trees are often over 10 years old before significant production occurs. Recently, shellers have complained about problems with fuzz (packing material which adheres to the kernel) and embryo rot on 'Stuart'. Desirable

'Desirable' (Figure 2.3) is recommended in more southeastern states than any other variety and is slowly replacing 'Stuart' as the cultivar of choice among growers. Yield is usually consistent, although it does have alternate bearing years following a heavy crop. 'Desirable' is in great demand both as an in-shell or

16 / Ray E. Worley

Figure 2.3.

'Desirable' pecans photo by Herb Pilcher.

shelled nut and thus brings a premium price on the market. The nut shape is oblong with blunt apex and slightly enlarged and rounded base. Upon shelling, a high percentage of mammoth halves are produced. Excellent management is required to overcome a weak tree structure and susceptibility to scab, leaf scorch and cold injury. Schley

Schley (Figure 2.4) is not currently recommended for planting, but it is included because of the large number of old trees in production and the excellent quality of the nut. This extremely thin-shelled nut often exceeds 60% kernel and is often considered synonymously with the term "papershell". Birds can easily peck through the thin shell causing extreme losses. The long, smooth, plump, bright golden colored kernel is seldom exceeded in eye appeal by any variety. 'Schley's' extreme susceptibility to scab and other diseases, insects, and low yield make it extremely difficult to manage at a profit. Western Schley

'Western Schley,' commonly called 'Western' (Figure 2.5) is to the arid west what 'Stuart' is to the humid southeast. Extreme scab susceptibility precludes 'Western's' commercial production in the southeast although its record has been good in fungicide treated experiments at the Georgia Coastal Plain Experiment Station (Worley 1985a). 'Western' is a long, thin-shelled nut which apparently

Figure 2.4.

'Schley' Pecans photo by Herb Pilcher.

Figure 2.5.

'Western Schley' pecan photo by Herb Pilcher.


18 / Ray E. Worley

has better quality nuts in more arid areas of the southwest than in the humid southeast. Thompson and Young (1985) reported 57 nuts/lb (26 nuts/kg) and 59% kernel. One sheller has complained that 'Western's' length sometimes causes excessive chipping of the kernel halves during mechanical shelling. 'Western' is not an attractive nut for the in-shell trade when grown in the southeast, but the thin shell often obscures the high percentage kernel. Gloria Grande

Tree shape and appearance of 'Gloria Grande' is almost identical to 'Stuart.' The nut however is much larger than 'Stuart,' but otherwise nut characteristics are similar (Figure 2.6). The medium shell thickness and resulting low kernel percentage in some years is detrimental. 'Gloria Grande's' capacity to bear large and consistent crops of large nuts after the tree is mature and resistant to scab are strong points. 'Gloria Grande' has shown variability in percentage kernel and kernel color (Worley 1978). Cape Fear

Nut size and shape of 'Cape Fear' are similar to 'Stuart,' but the shell has characteristic rust colored markings (Figure 2.7) (Worley 1976). The bright golden kernel color and medium-thin shell makes this variety attractive for the in-shell and shelled trade. 'Cape Fear' has shown an early tendency to overload and bear alternately with poor quality nuts being produced in the heavy crop years. Pruning and irrigation have improved the variety's quality performance. Sumner

'Sumner' is very similar to, but larger than, 'Schley' in nut appearance (Figure 2.8) and probably has 'Schley' as a parent. The thin shell makes it attractive for both the shelled and in-shell trade; however, the maturity date may be too late for the early market. The variety is noted for its precocity. 'Sumner' frequently drops a conspicuous amount of nuts during the water stage which may improve quality of the remaining nuts. Elliott

This tear-drop shaped nut is a favorite of many for its hickory nut flavor and attractive kernel (Figure 2.9). The thick shell and small size make it difficult to shell by hand. 'Elliott's' attractiveness when shelled and excellent flavor make it a popular item for use as hors d'oeuvres and specialty snacks at weddings and other social functions. The circular kernel halves are plump and bright colored. Buyers who recognize 'Elliott' for its special qualities should pay a premium for it, but too often it brings only seedling prices. 'Elliott' has medium precocity

Figure 2.6.

'Gloria Grand' pecans photo by Herb Pilcher.

Figure 2.7.

'Cape Fear' pecans photo by Herb Pilcher.


Figure 2.8.

'Sumner' pecans photo by Herb Pilcher.

Figure 2.9.

'Elliott' pecans photo by Herb Pilcher.


Pecan Production / 21

Figure 2 .10.

'Wichita' pecans photo by Herb Pilcher.

and early season nut maturity, but tends to alternate bear. Nut quality in the "on" year is usually good. Wichita This 'Halbert' x 'Mahan' cross, made in 1959 (Figure 2.10) received much publicity shortly after being released by the USDA. 'Wichita' is still popular in the western part of the pecan belt, but its extreme susceptibility to scab and the water stage split syndrome have eliminated it as a profitable variety for most growers in humid areas. The water stage split, apparently caused by excessive internal pressure (Prussia et al. 1985; Worley and Taylor 1972), may cause over half of the nuts to drop in mid-August. Growers in the eastern pecan belt have found it almost impossible to control scab when grown in concentrated stands in years of high rainfall. This elongated thin-shelled nut is of excellent quality. It is a good nut for both the shelled and in-shell trade, but the kernels tend to darken quickly in storage. Curtis 'Curtis' is an old variety with good scab resistance that has been popular in Florida. 'Curtis' nuts are frequently planted as rootstocks for grafting and budding. The elongated nuts are small and thin-shelled, but have good quality kernels (Figure 2.11). The small size of nuts and low yield prelude use of 'Curtis' in commercial plantings, but its disease resistance causes it to be recommended for yard planting where trees will not be sprayed. There is a slight flecking discoloration on the testa of the kernels, but few people will find it objectionable.

22 / Ray E. Worley

Figure 2 .11.

'Curtis' pecans photo by Herb Pilcher.


Old trees of 'Maramek' are restricted to Oklahoma where it has excelled. This large nut is reported to produce 45 nuts/lb (20 nuts/kg) with 59% kernel (Figure 2.12). This long cylindrical nut with medium shell thickness is prized in Oklahoma. Further testing in the eastern belt is needed before being recommended there. Data obtained from young trees indicates that 'Maramek' may have promise in the southeast. Woodard

'Woodard' was released by the University of Georgia in 1982 (Worley 1982a). It is one of the thinnest shell nuts in existence. The nut appears flattened on two sides with an enlarged apex end (Figure 2.13). The packing material extends from the inner septum out around the kernel and almost joins that of the dorsal grooves thus giving the appearance of a loose inner shell. Yields of 60% kernel are not uncommon. This variety is ideal for the person who cracks nuts by hand, because it can be easily cracked between the fingers and thumb of the hand. The thin shell causes cracking problems during mechanical harvest and subsequent handling and storage. 'Woodard' must be handled very gently in order to prevent losses. 'Woodard' usually has a long shelf-life. Shucks are susceptible to powdery mildew, but damage is superficial on the shuck and effect on the kernel is small.

Figure 2.12.

'Maramek' pecans photo by Herb Pilcher.

Figure 2.13.

'Woodard' pecans photo by Herb Pilcher.


24 / Ray E. Worley

Figure 2.14.

'Moneymaker' pecans photo by Herb Pilcher.


Old orchards in the eastern belt are likely to have trees of 'Moneymaker.' This round to slightly oblong nut with enlarged base and thick shell produces kernels of variable quality (Figure 2.14). When trees are overloaded, nuts may be poorly filled with low oil content and woody taste. Well filled nuts are of good quality. Alternate bearing is common. The thick shell and small size prevents high percentage kernel. Poor quality and low price are causing many growers to remove 'Moneymaker' in the thinning operation. Frotscher

Many old orchards in the eastern pecan belt still contain 'Frotscher' trees. This cylindrical, thin shelled, medium-late maturing nut is a classical poor quality nut (Figure 2.15). Nuts of this variety mixed in a lot may substantially lower the price received. The kernel testa contain visible darkened veins and kernel halves are frequently thin and poorly filled. The nut is fairly attractive as an inshell nut and is easily shelled. 'Frotscher's' use as a shelled nut would be limited to chopped meats and candy or bakery uses where eye appeal would not detract. This variety is one of the first to be removed in thinning operations. The variety 'Big Z' produces nuts practically identical to 'Frotscher.'

Pecan Production / 25

Figure 2.15.

'Frotscher' pecans photo by Herb Pilcher.

Horticultural Practice

Most horticultural practices have an effect upon quality. Poor quality is sometimes difficult to explain (Finch and Van Hom 1936). Production practices will be presented in chronological order, and then discussed in relation to the effects of each factor on pecan quality. During the early winter the orchard is cleaned of debris. Low limbs that inhibit rapid and safe passage of equipment through the orchard, deadwood and broken snags are removed. Pruning to shape and balance the tree and to remove forks and crows-feet is done to prevent potential limb breakage or "splitouts." Overcrowded orchards are thinned by removal of seedlings and poor-performing varieties such as 'Frotscher,' 'Mobile' and 'Moore.' If additional thinning is needed, a plan such as removal of alternating diagonal rows is usually followed. Fertilization and liming to a ph>6.0 is usually done in spring, although it can be done at any time. Spraying for insect and disease control begins at or before budbreak and may continue through mid-September. Irrigation is an integral part of a good pecan production program. Trees may need supplemental water at any time while trees are in leaf. In the southeast, a spring and fall drought can be expected every year. In the western pecan belt, practically all the tree's water needs must be supplied by irrigation. Drip or microsprinkler irrigation is used mainly as supplemental irrigation. If irrigation supplies most of the water for the trees, growers usually use sprinkler or flood irrigation. Harvest, the final horticultural practice, will be covered in the next section.

26 / Ray E. Worley

Various floor management plans may be used. The most popular is to use a herbicide strip within the tree row and a close-mowed sod between rows. One variation of this is to use a cover crop (usually a legume) in row middles to attract predators of pecan pests. Winter legumes are usually allowed to reseed before mowing. Certain summer legumes such as soybeans should be avoided, because they attract stink bugs and leaf-footed bugs. Feeding of these bugs causes kernel spot in the fall, which is one of the most serious quality defects of pecans. Intercropping may be done to a limited extent when trees are young. Grazing has been practically discontinued due to spraying restrictions and fecal contamination of pecans at harvest. Irrigation can dramatically improve nut quality if the season is dry. Irrigation has been reported to improve kernel quality as expressed by percentage kernel, kernel grade, percentage fill, or nut specific gravity (Alben 1958; Daniel and Heaton 1984; Heaton, Daniel and Moon 1982; Ismail 1978; Stein, McEachern and Storey 1989; Worley 1982b) (Table 2.2). Percentage kernel increased as drip irrigation rate increased from 0 to 238 liters/day/tree in Texas (Ismail and Storey 1978). In dry years, irrigation during nut sizing in July and August increased nut size (Alben 1958; Madden 1969; Romberg, Smith and Crane 1959; Stein, McEachern and Storey 1989; Worley 1982b). If trees are overloaded, application of water during the sizing season may reduce percentage kernel by creating more space in nuts than the photosynthesis process can fill. Some growers withhold water in late July and early August to prevent excessive size then apply irrigation during the filling stage to insure that the nuts are filled. The method of irrigation producing the best pecan quality would depend on location and local conditions. In Arizona, flood irrigation produced larger and better filled nuts than drip irrigation (Kilby 1974). Vivipary (sprouting of nuts while still on the tree) is a serious problem in southeast Texas and to a smaller extent at other locations. Sprouting of nuts renders them unmarketable. Vivipary was reduced by late season irrigation (Stein, McEachern and Storey 1989). Orchards that have had the best of care and are in a highly vegetative state in October are most affected by vivipary. "Sticktights" are nuts that do not shed the shuck at harvest. Insufficient moisture in the fall is a major cause of sticktights. Moisture is required for shucks to remain turgid and for the abscision layers to form at the sutures and at the peduncle. Irrigation can prevent or greatly reduce the sticktight problem (Table 2.3) (Stein, McEachern and Storey 1989; Worley 1982b). The shucks of sticktights usually must be removed before nuts can be marketed. Kernels from sticktights are usually of lower quality than kernels from nuts of the same tree whose shucks opened normally (due to premature death of the shuck which contains the vascular system which feeds the kernel). Nutritional status can affect nut quality. High nitrogen rates increase the nut set and reduce nut size (Heaton 1969; Worley 1990a) (Table 2.4) and percentage fancy grade kernel (Worley 1990a). Percentage kernel was reduced, but total

Pecan Production / 27 Table 2.2. Percentage kernel and nutsllb (kg) for three varieties of pecan as affected by drip irrigation (1978).1 Elliott



Drip Irrigation Treatment

Kernel (%)

Nutsllb (kg)

Kernel (%)

Nutsllb (kg)

Kernel (%)

Nuts/lb (kg)

No irrigation Irrigation on 1 side Irrigation on 2 sides

49.8 a2 51.5 ab 52.1 b

81 (36) b 77 (35) a 78 (35) a

41.8 a 48.7 b 50.3 b

65 (29) c 54 (24) a 58 (26) b

45.3 a 46.3 ab 48.1 b

81 (36) b 78 (35) a 74 (33) a


Data include all harvested nuts. Those in the shuck were deshucked prior to quality determination.

2Means within the same column with the same letter are not significantly different.

Table 2.3. Yield of nuts and percentage of sticktights for 'Desirable: pecans as affected by drip irrigation, Albany, GA 1978. Yield lb/a (kg/ha)


Irrigation treatment No irrigation 6 emitters/tree on one side 3 emitters/tree on each of 2 sides

800 (880) 2046 (2251) 2047 (2252)

52 1



"Sticktights are nuts that do not fall free of the shuck.

Table 2.4. analysis. Leaf N" (%) N2.25 N2.50 N2.75 N3.oo AN Leaf N" (%) N2.25 N2.50 N2.75 N3.oo AN

Pecan nut weight as affected by Nitrogen (N) application based on leaf Nut wt (g/nut)" 1973 8.3 7.5 8.1 6.7 6.2

c be c ab a

1981 9.7 9.8 9.5 8.7 7.8

c c c b a

1974 9.6 9.9 9.3 9.9 9.3


a a a a a

8.4 b 8.1 b 8.4 b 7.3 a 7.5·a



be c be ab a

8.8 b 9.1 b 9.3 b 8.6 b 7.8 a

8.1 8.3 8.0 7.7 7.5

1976 8.4 8.4 8.5 7.8 7.2

c c c b a

1984 9.3 9.3 8.9 8.8 8.5

c c b ab a

1977 8.3 8.7 8.3 9.5 7.2


1979 9.0 9.0 9.2 9.0 8.5

a a a a a

1980 5.4 be 5.4 be 5.8 c 4.8 b 4.2 a

b b b a ab

7.6 b 7.4 ab 7.3 ab 6.8 ab 6.6 a





8.1 b 7.9 b 7.8 ab 7.6 ab 7.1 a

9.3 b 8.9 ab 8.7 ab 8.8 ab 8.3 a

8.4 b 8.5 b 8.2 b 7.1 a 6.8 a

8.3 b 8.4 b 8.0b 7.9 b 7.3 a

Adapted from Worley (1990). "Nitrogen at 112 kg ha- I was applied to each tree only when the previous season's leaf analysis was below the specified thresholds of 2.25% (N2.25), 2.50% (N2.50), 2.75% (N2.75) or 3.00% N (N3.oo), except that treatment AN received 224 kg ha- I annually regardless of leaf analysis. b

Mean separation within years by GLM with PDIFF option P = 0.05.

28 / Ray E. Worley

kernel was increased by increasing nitrogen rate in another study (Heaton 1969). High N application reduced oil concentration in the kernel (Hunter 1964). Oil concentration was negatively correlated with leaf N (Hunter and Hammar 1956). The best compromise for nut size, yield, and profit was to add 100 Ibs N/a (112 kg/ha) when leaf N was less than 2.75% (Worley 1990a). In another study, nut size and kernel quality were similar when 100 or 200 lbs/a of N (112 or 224 kg/ ha) was applied all or part through the irrigation system, but nut size was reduced when 200 lbs/a of N (224 kg/ha) was applied without irrigation (Worley 1990b) (Table 2.5). Concentration of N applications within a radius as small as 15 ft. (4.6 m) was not detrimental to nut size and kernel quality (Worley 1989). Pecan nut quality and leaf P concentrations are extremely difficult to influence by soil applications of P. Massive applications of up to 13 ,369 lbs P/alyr (14,705 kg/halyr) caused only a small increase in nut size in one study (Sparks 1988). Adequate K is necessary for good kernel quality and high oil concentration. Oil concentration was positively correlated with leaf K and negatively correlated with the N/K ratio (Hunter and Hammar 1956). Oil content was increased slightly (max. of 2.5 percentage points) by applying nitrate as potash sprays (Hunter 1966, 1967). Good control of leaf feeding insects usually increases the supply of reserves produced by photosynthesis, which is necessary for good nut fill and large nut size (Dutcher et al. 1984). This control does not necessarily have to come from use of insecticides. Pecan quality and yield were better and net returns were greater from pest management than from use of conventional pesticides (Gentry and Smith 1982). Webworms, walnut caterpillars, phylloxera, aphids, mites and many other pests feed on pecan leaves and indirectly reduce kernel quality (Osborn et al. 1966). Insects, such as the nut casebearer, which feed on nuts and cause them to drop before maturity, usually reduces yield, but may increase the quality of the remaining nuts by reducing competition. A large portion of nuts, initiated in the spring, drop naturally before harvest. If insects remove some of these, then those that drop from other causes are reduced. In years where trees have a crop overload, feeding by the nut casebearer could be beneficial. Feeding by the hickory nut curculio and hickory shuckworm before shell hardening also causes nuts to drop and thus enhances quality by reducing crop load. Feeding by the hickory shuckworm after shell hardening reduces nut photosynthesis by severing the xylem vessels which supply nourishment to the kernel. The result is sticktights with poorly filled kernels (Calcote, Hunter and Thompson 1984; Payne and Heaton 1975; Welch and van Cleave 1970). Feeding of adult pecan weevils during the water stage causes nuts to drop. These inedible nuts must be removed during harvest. They are usually very light and are easily removed by moving air. Shriveled kernels occur when the female punctures the integument during the dough stage. Black spots occur when the puncture penetrates only into the integument (Hall and Eikenbary 1983; Hall and

Pecan Production / 29 Table 2.5. 'Stuart' nutsllb count as affected by drip irrigation and jertigation, Plains, GA Nuts/lb countb Treatments 200 Ibs/ A N be" no irrigation 200 Ibs/ A N be drip irrigation 100 Ibs/A N bc 100#/A fertigated o Ibs/A N bc 100 #/A N fertigated

1980 1981 1982 1983 1984 79 60 63 61

b a a a

81 63 62 59

b a a a

66 65 65 68

a 68 b 62 b a 60 a 57 a a 62 a 59 a a 60a 58 a


1986 1987 1988

64b 62 a 62 ab 61 a

94 b 72a 73 a 70 a

70 65 66 65

b a a a

141b 136a l36ab l34a

207b 158a 160a 154a

154b 143a 145a 143a

70 61 63 61

b a a a

Nuts/kg countb 220 kg/ha N be" no irrigation 220 kg/ha N be drip irrigation 11 0 kg/ha N bc 11 0 kg/ha fertigated o kg/ha N be 110 kg/ha N fertigated

173b 132a 138a 134a

178b 138a 136a l30a

145a 143a 143a 150a

150b 132a 136a 132a

136b 125a 130a 128a

154b l34a 138a 134a

"be = broadcast "Mean within columns with the same letter are not significantly different.

Hedger 1981). Weevil damaged pecans also contain many other decay organisms which damage the kernel. Some of these are Alternaria, Epicoccum, Pestilotia, Monochaeta, Cladosporium, Fusarium, Aspergillus, Phoma, Rhizopus and Trichothecium (Wells and Payne 1984). Many of these are also present in nondamaged nuts. Weevils oviposit in the kernels and the hatching larvae feed on the kernels. The larvae bore exit holes in the shell about harvest time and burrow into the soil where they remain for two years. Visible exit holes are sure signs of weevil problems and greatly reduce the price received for nuts. The presence of weevils before they bore the exit hole is difficult to detect visually. Sometimes the shuck does not open normally. Both the loss of the infested nuts and the removal of weevil larvae and weevil damaged nuts adds greatly to the cost of processing nuts. Feeding of plant bugs, mainly the southern green stink bug and leaf footed bug, causes black pit and kernel spot. Black pit is a discoloration of the interior of the young pecan nut. The affected nuts drop prematurely. The discoloration is darker than that of aborted nuts and the shucks cling tightly to the shell. Kernel spot develops when plant bugs puncture the nut during and after the dough stage. The spots are sunken, rancid, and very bitter tasting (Poles 1974). Nuts with black pit are removed in the cleaning process during harvest. Nuts with kernel spot cannot be detected before cracking and present a serious problem to buyers. When a crack test is made, many buyers discard any kernel half with a kernel spot. USDA grades allow for breaking the spot out of the kernel. Kernel spot is a very serious quality defect and, if abundant, may cause the entire lot to be unmarketable. Diseases that damage leaves and reduce the photosynthetic area usually reduce

30 I Ray E. Worley

kernel quality and nut size. Insufficient photosynthate causes wafering (thin poorly filled kernels) of kernels and reduced size. Scab (Cladosporium caryigenum) is the most serious of the leaf diseases. Downy spot, brown leaf spot, vein spot, zonate leaf spot, leaf blotch and liver spot occasionally cause problems (Osburn et al. 1966). Diseases that affect the nut also seriously reduce kernel quality. If scab infected nuts survive, they are usually small with poorly filled kernels. Late season scab infections cause only slight quality damage (Gottwald and Bertrand 1983, 1988). Light infection of nuts by mildew probably causes little damage; however, heavy infection decreased kernel oil, protein and free fatty acids by 8.6, 22.3 and 73.1 %, respectively, and increased moisture by 13.6% (Gottwald, Wood and Bertrand 1984). Infection of kernels by Aspergillus fiavus which produces aflatoxin was feared to be a problem on pecan, but an extensive sampling revealed only one sample with a violative level (20 ppb) of aflatoxin. This was a late season weevil infested sample (Wells and Payne 1976). Controlled atmosphere storage with 30% CO 2 killed weevil larvae and reduced microflora levels (Wells and Payne 1980). Shuck disease is manifested in two syndromes which seriously reduce nut quality and often make nuts unmarketable. Shuck dieback, sometimes called tulip disease, because a small portion of the nut apex opens prematurely, has been associated with premature girdling ofthe peduncle and is primarily associated with 'Success' (Stein and McEachern 1983). Sticky shuck or stem end blight has been associated with a fungus disease affecting nuts during the water stage (Stein and McEachern 1983). Sunken black shiny lesions form on the shuck and the endosperm turns brown or dies. Various irrigation treatments, fertilizer treatments, and ethephon growth regulator treatments had no effect on either of these maladies (Stein and McEachern 1983). Recently three late season diseases which either destroy the kernel or greatly reduce the kernel quality have been identified. Phytophthora cactorum rots the entire nut beginning at the stem end in the fall after a rainy period. Glomerella cingulata is associated with premature necrosis and "tuliping" of the shuck in August and September. Erwinia herbicola is associated with a shuck blackening and kernel rot during the water stage. Later a caramel colored discoloration occurs on the inside of the cotyledon halves (Reilly 1989). One of the most consistent effects of pruning is increasing nut size as shown by increased nut weight or nut volume (Anon 1967; Crane 1932a&b; Crane 1933; Crane and Hardy 1934; Crane et al. 1935; Hardy 1947; Managan, Coonrod and Storey 1984; Smith 1938; Storey, Madden and Garza-Falcon 1970; Worley 1985b; Worley 1987). Hedge pruning decreased nut volume (Worley 1985b). Heading increased percentage kernel and kernel grade (Storey, Madden and Garza-Falcon 1970). Selective limb pruning increased kernel grade and percentage kernel in dry years (Worley 1987). Pruning increased percentage kernel over thinning (Smith 1938).

Pecan Production / 31

In other studies, pruning had no effect on percentage kernel (Overcash and Kilby 1973; Crane and Hardie 1934; Malstrom 1981; Malstrom and Haller 1980) and had little effect on specific gravity of 'Pabst' (Crane and Hardie 1934) although it increased specific gravity of other cultivars (Crane and Hardy 1934; Storey, Madden and Garza-Falcon 1970). Pruning increased percent fill of some cultivars (Crane 1933; Crane and Hardy 1934; Storey, Madden and Garza-Falcon 1970), but had little effect on fill of nuts of 'Pabst' (Crane and Hardie 1934). Pruning increased value of nuts/a over thinning (Smith 1938). Thinning of trees increased nut size (Alben 1958; Romberg, Smith and Crane 1959) and percent kernel (Alben 1958). Thinning the trees increased nut specific gravity (Alben 1958) in some instances and decreased it in others (Romberg, Smith and Crane 1959). Opening of the tree canopy by pruning or tree thinning usually reduces disease and improves spray coverage (Cooper 1983). Heading decreased shuck disease (Storey, Madden and Garza-Falcon 1970). Pruning reduced preharvest germination of 'Buckett' when compared with thinning (Smith 1938). Pruning reduced downy spot damage more than thinning and increased foliage retention of 'Burkett' more than thinning (Smith 1938). The use of growth regulators to control pecan tree size has had variable effects on nut quality. Alar (daminozide) increased shuck disease, percentage kernel, nuts/lb., nut specific gravity, percentage fill, kernel grade and nut size, and delayed maturity (Storey, Madden and Garza-Falcon 1970; Hook and Storey 1971). Predators cause extensive losses of pecans each year. Blue jays frequently cause the greatest damage (Batcheller, Bisonnette and Smith 1982); however, crows and squirrels also cause serious losses. Losses are noticed more in light crop years, because the amount taken each year is similar. The food supply throughout the year largely determines the number of predators. Empty open shucks in the tree and no nuts on the ground are telltale signs of bird depredation. These predators usually take the best nuts and leave the faulty ones. The main quality damage would be the pecking of holes in thin shelled nuts by blue jays. Ground conditions which delay harvest would likely reduce nut quality. There were no consistent differences in nut quality when the orchard floor was grazed, clean cultivated, intercropped or kept in a closely mowed natural sod, but, in some years, nut size was reduced by grazing (Worley 1973). Nut size was reduced when oats were grown for hay (Kilby 1979). Floor management systems which compete with the tree for water and nutrients are thus likely to reduce nut size.

Harvesting The best quality nuts are those that are harvested soon after the shucks open. Oil content of 'Wichita' and 'Desirable' peaked just before shuck split. Nuts of

32 / Ray E. Worley

these varieties harvested prior to shuck split would have suboptimal oil content and lower quality (Eddy and Storey 1988). Nuts sold early in the season are usually most profitable (Mizelle and Westberry 1989). Green shucks can be removed from harvested nuts by dipping them in 3000 or 6000 ppm Ethrel and storing at 32°C (90°F) for five days, but this material has not been cleared for this use. These treated nuts had lower oil than naturally ripened nuts (Love and Young 1971). Once the kernel is mature it begins deteriorating. Early harvest also reduces the exposure time to predators. Nuts must go through a drying process either on the tree, on the ground, or through mechanical means before they can be placed in bulk storage. Cattle or other animals should be removed from the orchard long before harvest. Bacterial contamination of nuts is much more likely where cattle have grazed (Marcus and Amling 1971). Nuts may also be contaminated from wildlife or the hands of workers. Nuts must be shaken from the tree in order to accomplish early and rapid harvest. Shaking was originally done by climbers with poles. Later cable shakers were devised using tractor mounted eccentric bearings attached to a steel cable. A climber would attach the cable to a limb. The tractor operator would then tighten the cable and engage the eccentric bearing which caused the limb to vibrate. Cable shakers were a big improvement over the pole method, but they were still very slow and very dangerous. Limbs had to be fairly small and sometimes the climber had to climb 30-40 ft. (8-13 m) high or higher in order to reach limbs small enough to shake. Later boom shakers replaced the cable shakers, then in the 1960s, the large self propelled shakers which clamped on the trunk or reached lower limbs replaced the boom shakers. This type shaker resembles either a giant monkey wrench or a giant pair of scissors mounted on wheels. Smaller versions of trunk shakers are tractor mounted. It is important to insure that the jaws are tight in order to prevent damage to the cambium layer underneath the bark of the tree. Early shaking while the bark slips is more likely to damage the tree. Orchard Machinery Corporation (Yuba City, Calif.) makes a motorized catch frame that can be used on small trees. The large size required and the amount and size of limbs shaken out makes it impractical to use catch frames on large pecan trees. Catch frames must be used very early in the season in order to avoid having free falling nuts on the ground. Dehullers and driers must be used when harvest is early enough for catch frames. Once nuts are on the ground, it is urgent that they be picked up rapidly. Warm moist soil makes conditions ideal for mold development. Many pecans, especially those produced by yard trees, are still harvested by hand. Most large growers sweep the nuts into windrows. The sweeper is usually equipped with a blower which blows the nuts from around tree trunks and cleans the herbicide strip. Sweepers may be tractor mounted or self-propelled. The windrow contains good pecans, bad pecans, shucks, leaves, sticks, rocks and anything else that is loose

Pecan Production / 33

on the orchard floor. The contents of the windrow are then picked up by the harvesting machine where a combination of screens, conveyors, and blowers separate most trash from good nuts. A blast of air removes leaves, shucks and other light material. Screens remove particles larger and smaller than pecans. These materials are returned to the orchard floor where they decompose and contribute to recycling nutrients through the tree. Good nuts and foreign materials of similar size and weight are deposited into dump trailers pulled behind the harvester. Nuts are then hauled to the cleaning plant for final cleaning and drying. The cleaning plants may be large central units used by many growers or smaller farm operated units. Nut quality is greatly reduced if shells are cracked during the various harvesting processes. The number of cracked nuts increases with each additional step (Reid and Heaton 1977). Delaying harvest and high temperatures increase darkening of kernels (Kays 1979). Harvest could be hastened if shucks could be made to open earlier. Ethephon applications did hasten shuck opening but caused unacceptable leaf abscision (Wood 1989). An incomplete list of manufacturers of pecan harvesting equipment is presented below. This listing in no way is an endorsement of a product to the exclusion of others. Models change frequently and are not listed. Blowers Flory Industries, P.O. Box 908, 4737 Toomes Rd., Salida, CA 95368 Weiss Pecan Equipment Co., Hwy. 93, Baconton, GA 31716 Weiss/McNair, Inc., 531 Country Drive, Chico, CA 95928 Catch Frames Orchard Machinery Corporation, 2700 Colusa Highway, Yuba City, CA 95991 Cleaners Gene M. Jessee, Inc., 1627 Nord Ave., Chico, CA 95926 Nut Hustler Inc., Star Route, Box 18, Lampasas, TX 76550 Ron Kaiser Mfg., Inc., P.O. Box 673, Linden, CA 95236 Savage Equipment Co., Madill, OK 73446 Weiss Pecan Equipment Co., Hwy. 93, Baconton, GA 31716 Weiss/McNair, Inc., 531 Country Drive, Chico, CA 95928 Dehullers R.P. Barton & Co., 22398 S. McBride Rd., Escalon, CA 95320 Ron Kaiser Mfg., Inc., P.O. Box 673, Linden, CA 95236 Wizzard Manufacturing Co., 830 Cherry St., Chico, CA 95926 Harvesters Flory Industries, P.O. Box 908, 4737 Toomes Rd., Salida, CA 95368 Nut Hustler Inc., Star Route, Box 18, Lampasas, TX 76550 Ramacher Manufacturing Co., P.O. Box 506, Linden, CA 95236

34 / Ray E. Worley

Savage Equipment Co., Madill, OK 73446 Weiss Pecan Equipment Co., Hwy. 93, Baconton, GA 31716 Weiss/McNair, Inc., 531 Country Drive, Chico, CA 95928 Shakers FMC Corporation, 5601 East Highland Drive, Jonesboro, AR 72401 Kilby Mfg., 286 W. Evans Reimer Rd., Gridley, CA 95948 Nut Hustler Inc., Star Route, Box 18, Lampasas, TX 76550 Orchard Machinery Corporation, 2700 Colusa Highway, Yuba City, CA 95991 Savage Equipment Co., Madill, OK 73446 Sizers R.P. Barton & Co., 22398 S. McBride Rd. Escalon, CA 95320 Weiss Pecan Equipment Co., Hwy. 93, Baconton, GA 31706 Weiss/McNair, Inc., 531 Country Drive, Chico, CA 95928 Sweepers Flory Industries, P.O. Box 908, 4737 Toomes Rd., Salida, CA 95368 Ramacher Manufacturing Co., P.O. Box 506, Linden, CA 95236 Weiss Pecan Equipment Co., Hwy. 93, Baconton, GA 31716 Weiss/McNair, Inc., 531 Country Drive, Chico, CA 95928 References Alben, A.O. 1958. Results of an irrigation experiment on Stuart pecan trees in east Texas in 1956. Proc. Southeastern Pecan Growers Assoc. 51:61-68. Anon. 1967. Pruning increases pecan production. Okla. Fm. Res. Flashes March p. 1. Batcheller, Gordon R., I.A. Bisonnette and M.W. Smith. 1982. Blue lay depradations in Oklahoma Pecan orchards. Pecan Quarterly 16(2):19-22. Calcote, V.R., R.E. Hunter and T.E. Thompson. 1984. Nutrient flow through the pecan shuck into the nut and disruption of this flow by hickory shuckworm larvae. Proc. Southeastern Pecan Growers Assoc. 77:61-69. Cooper, J. 1983. Influence oftree spacing on the susceptibility of pecan to Cladosporium caryigenum. HortScience 18(2):167. Crane, H.L. 1932a. Two years' results of pruning bearing pecan trees. Proc. GeorgiaFlorida Pecan Growers Assoc. 26:44-51. Crane, H.L. 1932b. Results that may be expected to follow the pruning of bearing pecan trees. Nat. Pecan Assoc. Bul. 31:2-8. Crane, H.L. 1933. Results of pecan pruning experiments. Proc. Georgia-Florida Pecan Growers Assoc. 27:11-16. Crane, H.L. and F.N. Dodge. 1932. The pruning of pecan trees: methods and equipment to be used. Proc. Georgia-Florida Pecan Growers Assoc. 26:51-57.

Pecan Production I 35 Crane, H.L. and M.B. Hardy. 1934. Interrelations between cultural treatment of pecan trees, the size and degree of filling of nuts, and composition of kernels. J. Agr. Res. 49:643-661. Crane, H.L., M.B. Hardy, N.H. Loomis and F.N. Dodge. 1934. Growth and yield of pecan trees as affected by thinning the stand and other orchard practices. Proc. Amer. Soc. Hort. Sci. 32:33-37. Crane, H.L., M.B. Hardy, F.N. Dodge and N.H. Loomis. 1935. The effects of thinning the stand of trees and other orchard practices on the growth and yield of pecans. Proc. Southeastern Pecan Growers Assoc. 29:27-35. Daniel, J.W. and E.K. Heaton. 1984. Effect of drip irrigation on yield and quality of pecans in a dry year. HortScience 19:203. Demena, Richard. 1991. Pecan report. Federal-State Market News, Thomasville, GA 31799. Dutcher, J.D., R.E. Worley, J.W. Daniel, R.B. Moss and K.F. Harrison. 1984. Impact of 6 insecticide based arthropod pest management strategies on pecan yield, quality, and return bloom under four irrigation/soil fertility regimes. Environ. Entomol. 13:1644-1653. Eddy, M. and J. B. Storey. 1988. The influence of harvest date on oil and flavor development in 'Desirable' and 'Wichita' pecans. HortScience 23(3):782. Finch, A.H. and C.W. van Hom 1936. The physiology and control of pecan nut filling and maturity. Ariz. Agr. Exp. Sta. Tech. Bul. 62:421-472. Gentry, C.R. and J.S. Smith 1982. Evaluation of multi-pest management programs in Georgia pecan orchards. Protection Ecology 4:339-351. Goff, William D., Ray E. Worley and Ben T. Hagler. 1989. Renovating older pecan orchards. In Pecan Production in the Southeast a Guide to Growers, ed. William D. Goff, John R. McVay, and W.S. Gazaway, pp. 161-180. Ala. Coop. Ext. Ser. Cir. ANR-459. Gottwald, T .R. and P .F. Bertrand. 1983. Effect of time of inoculation with Cladosporium caryigenum on pecan scab development and nut quality. Phytopathology 73:714-718. Gottwald, T.R. and P.F. Bertrand. 1988. Effects of an abbreviated pecan disease control program on pecan scab disease increase and crop yield. Plant Dis. 72:27-32. Gottwald, T.R., B.W. Wood, and P.F. Bertrand. 1984. Effect of powdery mildew on net photosynthesis, dark respiration, and kernel composition of pecan. Plant Dis. 68:519-521. Hall, M. and R.D. Eikenbary. 1983. Impact of pecan weevil on pecan production. Proc. Southeastern Pecan Growers Assoc. 76:53-58. Hall, M.P. and G.H. Hedger. 1981. Impact of pecan weevil on pecan production in pest managed commercial orchards. Environ. Entomol. 10:668-672. Hardy, M.B. 1947. Progress report on attempts to control biennial bearing in pecans. Proc. Southeastern Pecan Growers Assoc. 40:54-62. Heaton, E.K. 1969. The effect of nitrogen fertilization on quality of pecan meats. Proc. Southeastern Pecan Growers Assoc. 62:42-45.

36 / Ray E. Worley

Heaton, E.K., J.W. Daniel, and L.C. Moon. 1982. Effect of drip irrigation on pecan quality and relationship of selected quality parameters. J. Food Science 47: 1271-1275. Hooks, R.F. and J.B. Storey. 1971. Effect of succinic acid-2, 2-dimethylhydrazide (SADH) and heading-back on pecans. HortScience 6:237-238. Hunter, J.H. 1964. Time of applying nitrogen to pecan trees in sod. Proc. Southeastern Pecan Growers Assoc. 57:18-22. Hunter, J.H. 1966. Progress report with sprays of nitrate of potash on pecans. Proc. Southeastern Pecan Growers Assoc. 59:46-50. Hunter, J .H. 1967. Nitrate of potash sprays on pecans. Proc. Southeastern Pecan Growers Assoc. 60:101-104. Hunter, J.H. and H.E. Hammar. 1956. Relation of oil contents of pecan kernels to chemical components of leaves as a measure of nutrient status. Soil Science 82:261269. Ismail, M.M. 1978. The influence of drip irrigation on vegetative growth, yield, nut quality, and leaf water potential of mature pecan trees. Dissertation Abstr. 7900980. Ismail, M.M. andJ.B. Storey. 1978. The influence of drip irrigation on vegetative growth, yield, and nut quality, on mature 'Stuart' pecans. HortScience 14:129. Kays, S.J. 1979. Pecan kernel color changes during maturation, harvest, storage and distribution. Pecan South 13(3):4-12,37. Kilby, M.W. 1974. Pecan drip irrigation in the lower El Paso Valley. Proc. Western Pecan Conference 8:103-108. Kilby, M.W. 1979. Orchard floor management for young pecan trees in the El Paso Valley. Pecan South 6(1):26-29. Love, J.E. and W.A. Young. 1971. Pecan quality: from beginning of harvest to consumption. Proc. Southeastern Pecan Growers Assoc. 64:95-97. Madden, G.D. 1969. Effects of supplemental irrigation on pecans. Proc. Texas Pecan Growers Assoc. 48:54-56. Malstrom, H.L. 1981. Effect of hedge pruning on light penetration, nut production, and nut quality of 'Western' pecan trees. Proc. Western Pecan Conference 15:4-25. Malstrom, H.L. and R.L. Haller. 1980. Consequences of hedge pruning pecan trees. Proc. Tex. Pecan Growers Assoc. 58:52-56. Managan, P., B. Coonrod and B. Storey. 1984. Preliminary study of pecan orchard rejuvenation. HortScience 19(2): 1984. Marcus, K.A. and H.J. Amling. 1971. (Escherichia coli) contamination of pecan nuts as influenced by method of harvest and cultural practices. Proc. Southeastern Pecan Growers Assoc. 64:43-46. Menges, Terry. 1985. Pecan varieties for Texas. Texas Pecan Growers Assoc. Proc. from the 63rd & 64th Ann. Conf. 63:6-8. Mizelle, W. O. and G. O. Westberry. 1989. Economics of early harvest. Proc. Southeastern Pecan Growers Assoc. p. 165-169. Osburn, M.R., W.C. Pierce, A.M. Phillips, J.R. Cole and G.E. KenKnight. 1966. Controlling insects and diseases of the pecan. USDA Agric. Hdbk. No. 240.

Pecan Production / 37 Overcash, J.P. and W.W. Kilby. 1973. The effect of method of pruning and training on yields of young pecan trees. Proc. Southeastern Pecan Growers Assoc. 66:63-7l. Payne, J.A. and E.K. Heaton. 1975. The hickory shuckworm, Laspeyresia caryana, pest of the pecan. Its biology, effect upon nut quality and control. Ann. Rept. North. Nut. Growers Assoc. 66:19-250. Poles, S.G. 1974. Plant bugs: one of the main culprits causing both black pit and kernel spot in pecans. Proc. Western Pecan Conference 8:70--72. Prussia, S.E., D.T. Campbell, E.W. Tollner and J.W. Daniell. 1985. Apparent modulus of elasticity of maturing pecans. Trans. Amer. Soc. Agric. Eng. 28:1290--1296. Reid, C.A. 1923. Pruning the pecan tree. Proc. Georgia-Florida Pecan Growers Assoc. 17:12-18. Reid, C.A. 1924. Further notes on pecan pruning. Proc. Georgia-Florida Pecan Growers Assoc. 18:44--49. Reid, J.T. and E.K. Heaton. 1977. The effect of mechanical harvesting and cleaning operations on shell breaking and nutmeat quality of pecans. Trans. ASAE 20:623-625. Reilly, C.C. 1989. Late season diseases of pecan. Proc. Southeastern Pecan Growers Assoc. 82:67-70. Romberg, L.D., C.L. Smith and H.L. Crane. 1959. Effects of tree re-spacing (thinning) on pecan tree growth and nut production. Proc. Tex. Pecan Growers Assoc. 38:60-75. Smith, c.L. 1938. Three years results of thinning the stand as compared with pruning thickly planted pecan trees. 1. Amer. Soc. Hort. Sci. 36:339-346. Sparks, D. 1977. Notes on the Stuart pecan. Pecan South 4(5):204-207. Sparks, D. 1988. Growth and nutritional status of Pecan in response to phosphorus. 1. Amer. Soc. Hort. Sci. 113:850--859. Stein, L.A. and G.R. McEachern. 1983. Pecan shuck disorders. Texas Pecan Growers Assoc. Proc. from the 63rd and 64th Ann. Conf. 63:22-24. Stein, L.A., G.R. McEachern and J.B. Storey. 1989. Summer and fall moisture stress and irrigation scheduling influence pecan growth and production. HortScience 24:60761l. Storey, J .B., G. Madden and G. Garza-Falcon. 1970. Pecan research 1965-69. Influence of pruning and growth regulators on pecans. Tex. Agr. Exp. Sta. PR 2709. Thompson, Tommy E. and Foutain Young. 1985. Pecan Cultivars Past and Present. The Texas Pecan Growers Assoc. College Station, Texas. Thompson, T.E., E.F. Young, Jr., H.D. Peterson, R.E. Worley, R.D. O'Barr, R.S. Sanderlin and L.J. Grauke. 1990. Three new pecan cultivars: Oconee, Houma, Osage. Pecan South 24(1):4-9. Wells, J.M. and J.A. Payne. 1976. Incidence of aflatoxin contamination on a sampling of southeastern pecans. Proc. Fla. State Hort. Soc. 89:256. Wells, J. M. and J .A. Payne. 1980. Reduction of microflora and control of inshell weevils in pecans stored under high carbon dioxide atmospheres. Plant Dis. 64:997-999.

38 / Ray E. Worley Wells, I.M. and I.A. Payne. 1984. Decay organisms of tree nuts and their control. Ann. Rept. Northern Nut Growers Assoc. 75:35-40. WeIch, 1.1. and H.W. van Cleave. 1970. Chemical control of the hickory shuckworm on pecans. In Pecan Research 1965-69. Texas Agr. Exp. Sta. PR-2719 Consolidated PR-2709-2722. Wood, B.W. 1989. Ethephon and NAA facilitate early harvesting of pecans. J. Amer. Soc. Hort. Sci. 114:279-282. Worley, R.E. 1972. An abnormal nut splitting problem of pecan (Carya illinoensis, Koch.). Hort Science 7:70-71. Worley, R.E. 1973. Effect of four floor management systems on parameters associated with growth and yield of pecan. J. Amer. Soc. Hort. Sci. 98:541-546. Worley, R.E. 1976. Performance of 'Cape Fear' at the Georgia Coastal Plain Experiment Station. Pecan South 5:42-43. Worley, R.E. 1978. 'Gloria Grande' pecan. Proc. Ga. Pecan Growers Assoc. 9:75-81. Worley, R.E. 1982a. Woodard pecan. HortScience 17:415-418. Worley, R.E. 1982b. Tree yield and nut characteristics of pecan with irrigation under humid conditions. J. Amer. Soc. Hort. Sci. 107:30-34. Worley, R.E. 1983. Performance of 'Stuart' pecan at the Coastal Plain Experiment Station. Proc. Ga. Pecan Growers Assoc. 14:19-27. Worley, R.E. 1985a. 'Western' in the east. Proc. Ga. Pecan Growers Assoc. 16:65-73. Worley, R.E. 1985b. Effects of hedging and selective limb pruning of Elliott, Desirable, and Farley pecan trees under three irrigation regimes. J. Amer. Soc. Hort. Sci. 110: 1216. Worley, R.E. 1987. Effect of pruning old noncrowded Stuart pecan trees to three heights. Proc. Southeastern Pecan Growers Assoc. 80:123-127. Worley, R.E. 1989. Can we reduce the area covered by Nitrogen application. Proc. Southeastern Pecan Growers Assoc. 82:171-174. Worley, R.E. 1990a. Long-term performance of pecan trees when nitrogen application is based on prescribed threshold concentrations in leaf tissue. J. Amer. Soc. Hort. Sci. 115:745-749. Worley, R.E. 1990b. Irrigation and nitrogen fertigation of old pecan trees. Proc. Southeastern Pecan Growers Assoc. 83:29-35. Worley, R.E. 1991. Performance of the newly-released 'Oconee' pecan through the 12th leaf at the University of Georgia Coastal Plain Experiment Station. Proc. Southeastern Pecan Growers Assoc. 84:104-109.

3 Pecan Physiology and Composition Ray E. Worley

Pecan Physiology and Composition

Pecan [Carya illinoensis (Wangenh.) C. Koch] is one of the few native cultivated plants in the United States. Early explorers found them growing wild along the Mississippi River and its tributaries. Pecans made up a large portion of the diet of the local American Indians in productive years. Alternate bearing was a problem even for the Indians. Pecans were spread to other areas by the early travelers. They are now grown in all the southern states from California to Virginia and extending as far north as southern Illinois and Iowa and into Mexico to the south. There are occasional reports of pecans being grown outside these ranges. They are also grown in limited quantities in other countries with similar climates. Commercial plantings are in Mexico, Israel and Australia. Bud break for pecans occurs in spring after buds of most other trees have broken. For the southeast this occurs about April 1. Catkin primordia, containing spikes of many male flowers, are formed the previous spring but remain dormant within the bud until bud break of the current spring. Pistillate flowers are completely separate organs formed at the terminals of healthy current season twig growth. Wind pollination occurs from mid-April until mid-May. After pollination the young nutlets grow very slowly until mid-July when rapid nut expansion begins. Vascular bundles enter the shuck at the peduncle, extend to the apex of the shuck, then fold back to the base of the shuck and enter the shell where they traverse the nut again along the inner septum and finally reach the placenta (Figure 3.1) (Calcote, Hunter and Thompson 1984). Most of the nut's volume is formed during an approximate four week period from mid-July to mid-August. During this rapid growth period the kernel consists of a liquid filled seed coat. This liquid endosperm later congeals and solid material is deposited on the interior of the seed coat. This forms the cotyledons or the two edible halves. C. R. Santerre (ed.), Pecan Technology © Chapman & Hall, Inc. 1994



Figure 3.1.

Cross-sectional diagram of a develop-

ment nutlet.

When the cotyledons are filled, ethylene is released which induces the shucks to split along the sutures. As nuts and shucks dry, the shuck opens fully and the nut is held loosely by the dried remnants of the vascular system which nourished the nut. The process of nut maturation and the chemical changes which occur are presented in more detail below. Development periods of the pecan fruit may be divided into: (1) that period from May to late August comprising the time from blossoming until the kernel begins to fill; and (2) the filling and ripening period. Most of the oil, protein, mineral, and acid-hydrolyzable polysaccharide content of the kernel develops during September. Practically all of the material from which oil and protein is formed must be brought in from outside the fruit during the filling period (Thor

Pecan Physiology and Composition / 41

and Smith 1935). In New Mexico, free-nucleate endosperm was first observed in mid-July when fruit had grown to 50% of their final length at 67 days after stigma receptivity (DASR) for 'Ideal' and 76 DASR for 'Western.' Maximum content offree-nucleate endosperm occurred 100 DASR in 'Ideal' and 109 DASR in 'Western' fruit. Ovary wall lignification was completed 119 DASR in 'Ideal' and 132 DASR in 'Western.' At this time, nut enlargement was complete. Cotyledon thickening required 36 and 43 days for 'Ideal' and 'Western,' respectively. The time from stigma receptivity to completion of cotyledon thickening in mid-October was 13 days longer for 'Western' than for 'Ideal' (Herrera 1990). The time frame for nut maturization is highly dependent on cultivar. At Brownwood, Texas, one early maturing clone had accumulated 24% of its final dry weight by July 23, while the average for all clones at this time was 11%. In general, the percentage of dry matter decreased about 5% during August and increased slightly thereafter until immediately before harvest, when increases were great due to nut and shuck drying. Total dry matter decreased during October for some late maturing clones, possibly indicating movement of photosynthate out of nuts during the root carbohydrate replenishing period. These decreases, which were the most obvious in 'Mahan' and its progeny clones, were not detected in early maturing clones. The existence of earlier filling clones indicates that this genetic trait can be increased by breeder selection. Clones with earlier and longer nut filling periods are needed to increase yields (Thompson 1982). The period of rapid intake of N, P, Mg, and K into 'Moore' nuts coincides with the period of rapid accumulation of oil, protein, and acid hydrolyzable polysaccharides. There was no evidence of movement of mineral elements from the shoot into the nut during the earlier period of nut development. These elements accumulated in the shoots more rapidly than they were used by the nuts. Calcium accumulated in the nuts during the period that they were increasing in size. Since kernel Ca is low, this accumulation indicates that Ca is important mainly in structural units (Lewis and Hunter 1944). Only a small amount of fertilizer elements are removed from the orchard in the crop. Hunter (1956) reported that a 1000 lb (460 kg) crop of nuts removed only 11 lbs (5 kg) N, 4 lbs (1.56 kg) P20 S (1.76 lbs P; 0.81 kg) and 4 lbs (1.8 kg) K20 (3.32 lbs K; 1.49 kg) from the orchard. Almost 30 years later Sparks (1975a, 1975b) reported very similar results. In Sparks' study, a 1000 lb (460 kg) crop of nuts (not including shuck) removed an average of only 18 lbs (8.3 kg) of elements (N, P, K, Ca, Mg, Mn, Fe, B, Cu, Zn, AI, Mo, Sr, and Ba) from the orchard. This 1000 lb (460 kg) crop included 8.5 lbs (3.9 kg) N, 1.9 lbs (0.85 kg) P, 3.78 lbs (1.7 kg) K, 3.3 lbs (1.5 kg) Ca and 0.50 lb (0.23 kg) Mg. About 70% of the elements taken up by the fruit were returned to the soil in the shuck. When the shuck decays these elements are released again for uptake by the tree. Potassium made up approximately 58% of the total elemental content of the fruit. All elements except Ca and Mo were higher in shuck than in shell. In Oklahoma, concentration of N, P, K, Ca, Mg, Zn and Mn in nuts increased

42 I Ray E. Worley

slowly until the tenth week after full bloom, then rapidly until fruit maturity. The rapid increase in element concentration corresponded to kernel growth. Dry weight and volume of the fruit also increased slowly until the tenth week, followed by a rapid increase until maturity (Diver, Smith and McNew 1983, Diver and Smith 1984). Shuck tissue is very high in K, while shell tissue is fairly low in most minerals except Ca and Mo. Kernel tissue is extremely low in Ca but will be able to supply the diet with reasonable levels of the other nutrients (Table 3.1) (Sparks 1975a, 1975b; Diver, Smith and McNew 1983; Diver and Smith 1984). Nut ontogeny progresses rapidly in the fall. In Israel the 'Delmas' nut reaches its full size at the beginning of September, while the shuck continues to grow for about four additional weeks. The liquid endosperm attains its maximal volume by the end of August and disappears during the first week of September. At about this time, potassium and lipids start to accumulate. The rate of accumulation of potassium in the shuck and lipids in the kernel is exponential. A linear relationship exists between the level of potassium in the shucks and lipids in the kernel. Extrapolation of the regression line indicates a critical potassium level in the shuck at ca. 1.57% of dry weight. Potassium analysis of the shucks was proposed as a physiological indication of the potassium status of the tree (Pe'er and Kessler 1984). An excellent report on the ontogeny of kernel development of 'Burkett' and 'Stuart' nuts in Austin, TX was published in 1935 (Thor and Smith). Oil synthesis began and was almost complete in September. 'Burkett' had 74% oil and 'Stuart' had 76% in the kernel. The kernel sugars were almost exclusively non-reducing sugars, probably sucrose, except for the very early watery stage. In other tissues, reducing sugars were the predominant forms. Total sugar/fruit increased to the middle of September, then decreased to the end of September during the period of rapid production of oil and protein. The sugar concentration of the kernel on a dry-weight basis as well as on a per kernel basis dropped rapidly in September until most of the oil had been formed, then non-reducing sugar accumulated rapidly until harvest. More than 50% of the sugar in the mature kernel was laid down in the last two weeks before harvest on October 18. This sugar apparently moved in from the shuck because there was no definite influx of sugar into the whole fruit. Acid hydrolyzable polysaccharides increased rapidly in the whole fruit during the summer when the shell and other structural parts were forming and more slowly after filling of the kernel began. The shuck and shell portions showed no important change in sugar after September (Thor and Smith 1935). Fertilizer experiments by Finch and van Hom (1936) did not clearly reveal the fundamental causes of poor filling, nor provide a dependable means of controlling it. Their studies revealed the following observations. Poor filling has occurred where water was supplied by irrigation and where fertilizer was added. Soil moisture and nutrition were apparently not the reason for poor filling. Poor filling when large crops are produced is sometimes ascribed to the number of

Pecan Physiology and Composition I 43 Table 3.1. Average mineral composition of shell, kernel and shucks of 'Farley' pecans at harvest. ppm







Shell 0.43 0.08 0.34 0.73 0.016 Kernel 1.17 0.28 0.40 0.03 0.075 Shuck 1.20 0.16 7.85 0.75 0.337

Mn Fe




81 21 13.9 6.2 8.6 62 34 9.5 10.1 45.0 451 35 22.0 6.6 13.3





29 1.89 16.1 13.7 14 1.95 3.7 10.9 208 1.57 45.7 49.9

Adapted from Sparks (1975).

nuts. The authors noticed small crops that did not fit well. The relationship between vegetativeness and nut filling was not clear. In strongly fruiting shoots, starch storage was found to reach a maximum in late July or early August after which the amount gradually diminished until early October. Starch stored in the shoots apparently served as a reserve for formation of the nut. Movement of starch out of the shoot started first at the shoot tip, next to the fruit and progressed basipetally. This removal of starch from the shoot in late summer was observed to be initiated somewhat before and then to proceed concurrently with the accumulation of sugars in the nut and their conversion to fats. Complete absence of starch was reached in some shoots before filling was complete. There appeared to be a relationship between vegetativeness, and quality of the nut, but it was not clear. Percentage of oil in the kernel was greatest with low vegetativeness. Sugar content of the kernel was greatest on highly vegetative trees which might have been caused by delayed conversion of sugars to oil. Nitrogen content of kernel was inversely associated with oil content. Total N on a per kernel basis was greatest in the largest kernels. Phosphorus content of kernel was not related to oil content, vegetativeness, filling or other characteristics of the nuts. An early study indicated that cultural practices had little effect on nut composition. In this study, composition of well cured, well-filled kernels was 70% oil, 10% protein, 10% easily available carbohydrate, 2.5% water, and 7.5% fiber and ash. Oil varied from 55-75% and protein from 8-18%. As the degree of filling increased, the oil content increased and the protein, carbohydrates, water and other constituents decreased as a result of dilution. Varieties varied greatly in composition. 'Schley' and 'Pabst' nuts were higher in oil by about 6 percentage points but had less protein than 'Stuart.' Nut size did not affect composition of equally well filled nuts (Hardy and Crane 1932, Crane and Hardy 1934). Oil content of 21 pecan varieties fluctuated between 64 and 75% and varied greatly between variety, year, and location. There was no significant correlation between oil content and variety nor between oil content and rancidity. Iodine number varied between 90.1 and 103.6 (Wells and McMeans 1978) which indicates variability in degree of unsaturation of component lipids. The oil content of pecan kernels appears to be reduced by high applications of nitrogen or elevated leaf N and increased by applications of potassium or

44 / Ray E. Worley

elevated leaf K (Hunter and Hammar 1956). Oil concentration was increased only slightly by applications of potassium nitrate spray (Hunter 1964, 1967). The timing of harvest is critical for maximizing oil concentration. Oil content of 'Wichita' peaked on October 15 and 'Desirable' peaked on October 25 which was prior to shuck split. Nuts of these varieties harvested prior to these dates would have sUboptimal oil content and lower quality (Eddy and Storey 1988). Oil in pecan kernels consists mainly of 16 and 18 carbon chain fatty acids containing 0 to 3 double bonds. Low N fertilized trees produced nuts having 6.1% palmitic (16:0), 1.1% stearic (18:0), 64.7% oleic (18:1), 27.3% linoleic (18.2) and 0.9% linolenic (18.3). Increasing the nitrogen fertilization rate increased the saturation and polyunsaturated, but decreased the monounsaturated fatty acids and increased the iodine number (Heaton 1969). Increasing the nitrogen rate then would increase the level of "bad" cholesterol from a nutritional standpoint. Increasing the iodine number means that the number of double bonds are increased and thus the nut would be more subject to going rancid when oxidation occurs at these double bonds. At Byron, GA yields were inversely correlated with nut weight and total oil content and directly correlated with refractive index and potassium concentration of the mature kernel. Six fatty acids were found in kernel oil but only palmitic, oleic, and linoleic were correlated with yield (McMeans and Malstrom 1982). Later the whole pecan fruit was found to contain, in addition to the above, linolenic, stearic, myristic, margaric and arachidic fatty acids. During endosperm expansion, fatty acids were present in small concentrations. During embryo and cotyledon expansion, fatty acids accumulate (Wood 1982a). Nut quality, in terms of flavor stability, or the persistence of fresh flavor in storage is related more to the chemical composition of the oil rather than directly to the oil content. 'Shawnee,' 'Shoshoni,' and 'Cape Fear' have low unsaturation values and store well while 'Wichita' and 'Moneymaker' have high unsaturation values which accelerates rancid flavor development. Pecans that store well for prolonged periods without going rancid have low unsaturation values, high oleic acid and low linoleic, palmitic and stearic acid concentration. Well-managed orchards with adequate irrigation usually have nuts with higher oil concentrations than poorly managed and non-irrigated orchards (Wells, McMeans and Payne 1980). Preliminary data from Texas (J.B. Storey, personal communication) and from our laboratory has indicated a large variation in the mono/poly fatty acid ratio among pecan varieties and even the same varieties grown at different locations. Although pecans are noted mainly for their oil content, they also contain proteins and carbohydrates. Kernel development was characterized by rapid accumulation of dilute acid and dilute alkali soluble proteins and a decline of buffer and alcohol soluble proteins during embryo and cotyledon expansion. Mature kernels (cv. Moneymaker) contained 7.8% proteins, consisting of 51% acidic glutelins, 27% alkali glutelins, 9% concentration alkali, 7% prolamine,

Pecan Physiology and Composition / 45

4% albumin and 1% globulin. Each fraction was composed of at least two proteins throughout kernel development. Proteins in each fraction were comprised primarily of neutral amino acids, but individual amino acid levels were highest for basic amino acids, with relatively high levels of lysine- and sulphur-containing amino acids. Electrophoresis of acid soluble glutelins revealed at least seven subunits with molecular weights of 102,58,37, 30,26, 19, and 16 (x 10000) (Wood and Reilly 1984). Major sugars found in the kernel, shell and shunk were fructose, glucose, sucrose and inositol. During endosperm expansion fructose and glucose rapidly accumulated and fatty acids were present in small concentrations. During embryo and cotyledon expansion, fatty acids accumulated and reducing sugars and inositol declined while sucrose increased (Wood 1982a). Small quantities of some chemicals in the kernel may influence color of the testa. Reversible color changes in pecan kernels are attributed to the concentration of iron-containing pigments in the outer layers of the testa. Kernel color was lightened upon exposure to SnC1 2 or H3P04 solutions. The color change was attributed to the reduction of Fe +3 to the Fe +2 state. Surface iron ranged from 15 to 21 ppm and total iron ranged from 78-99 ppm. From 18 to 22% of the total iron was surface iron. The percent color change ranged from 4-18% (Wandruszka, Smith and Kays 1980). This study indicates that the availability of O2 might affect testa color. Internal O2 levels between the shuck and shell increased after dehiscence from initial concentrations of 16-17 % to near that of the external environment after three weeks. Internal CO 2 concentration, conversely, decreased substantially after dehiscence. Treatment of nuts over the same physiological stages of development with 2.5, 5.0, 10.0, 21.0, or 100% O2 had little effect on the induction and development of the kernel's normal pigmentation (Kays 1977). Tannins may also affect color of the kernel. Percentage tannins ranged from 0.699 for 'Jackson' to 1.710 for 'Shoshoni.' Other concentrations for well-known varieties were as follows: 'Stuart'-O.736, 'Desirable'-O.742, 'Schley'0.789, 'Curtis'-O.839, 'Kiowa'-O.845, 'Sumner'-1.007, 'Farley'-1.11O, 'Wichita'-1.398 (Pones, Hanny and Harvey 1980). The high tannin content of 'Wichita' might be related to its rapid dark color development. Juglone is a chemical found in tissues of Juglandacae family and is sometimes thought to have herbicidal or fungicidal activity. Seasonal, species, and variety differences in juglone concentration of nuts were found. Juglone concentration ranged from a high of 2.94 mg/g in husks (shucks) to 0.088 mg/g in kernels. Highest levels of juglone occurred in September for 'Van Deman' kernels. Applications of indoleacetic acid (IAA), mepiquat chloride, and p-coumaric acid increased juglone concentration in nuts (Borazjani 1981). The range in critical physical and chemical characteristics of the shells of mature fruit (nuts) of pecan were assessed for 16 major varieties and two selections. Nut physical parameters varied widely among genotypes. Total nut weight

46 / Ray E. Worley

varied from 5.3 to 10.4 g, kernel weight from 2.8 to 5.1 g, shell weight from 1.6 to 4.1 g, packing tissue weight from 0.6 to 1.7 g and shell thickness from 0.62 to 0.98 mm. An even greater range was found among genotypes in the concentration of extractable phenolics which could be byproducts used in the resin and plastic industry. Extractable phenolics varied from 6.3 to 20.9% of the total shell weight (shell + packing tissue), from 0.06 to 1.5% in the shell alone and from 20.2 to 52.6% in packing tissue. Commercially separated samples of packing tissue contained 6.24% extractable pecan oils (Kays and Payne 1982). Pecan kernel development was characterized by an initial rapid localized expansion of testa and endosperm, which was closely associated with low levels of free and bound abscisic acid (ABA) and with high levels of gibberellin-like (GL) substances. Rapid cotyledon growth began with the termination of testa and endosperm expansion, which was subsequent to a sharp increase in both free and bound ABA. The rate of change for growth in kernel dry weight was highly correlated with the rate of change in levels of both free ABA (R2 = 0.86) and bound ABA (R2 = 0.88). Levels of GL substances (ng/g kernel), as measured by the dwarf pea and cucumber bioassays, were relatively low after the rapid accumulation of kernel dry weight, however, GL substances detected by the barley endosperm bioassay were high during the last 30 days of kernel development. Abscisic acid and GL substances seem to exercise a significant role in seed development (Wood 1984). Bioassays suggested that gibberellin A3, A4 and A7 were present in the liquid endosperm (Wood 1982b).

References Borazjani, A. 1981. Occurrence of juglone among walnuts and hickories: seasonal variations, presence among tissues, translocation, and the influence of growth regulators on concentration. Diss. Abstr. 42: 11. 4258-B. Calcote, V.R., R.E. Hunter and T.E. Thompson. 1984. Nutrient flow through the pecan shuck into the nut and disruption of this flow by hickory shuckworm. Proc. Southeastern Pecan Growers Assoc. 77:61-69. Crane, H.L. and M.R. Hardy. 1934. Interrelations between cultural treatment of pecan trees, the size and degree of filling of nuts, and the composition of kernels. J. Agric. Res. 49:643-661. Diver, S. G. and M. W. Smith. 1984. Influence offruit development on seasonal elemental concentrations and distribution in fruit and leaves of pecan. Commun. in Soil Sci. Plant Ana. 15:619-637. Diver, S.G., M.W. Smith and R.W. McNew. 1983. Seasonal changes in the mineral concentration of pecan fruit and leaves on fruiting and vegetative shoots. HortScience 18:167. Eddy, M. and J.B. Storey. 1988. The influence of harvest date on oil and flavor development in Desirable and Wichita pecans. HortScience 23(3):782.

Pecan Physiology and Composition I 47

Finch, A.H., and C.W. van Hom. 1936. The physiology and control of pecan nut filling and maturity. Ariz. Agr. Exp. Sta. Tech. Bu. 62:421-472. Hardy, M.B. and H.L. Crane. 1932. Can the composition of pecan nuts be changed by fertilizer and other cultural treatments? Nat. Pecan Assoc. Bull. 31:110-114. Heaton, E.K. 1969. The effect of Nitrogen fertilization on quality of pecan meats. Proc. Southeastern Pecan Growers Assoc. 62:42-45. Herrera, E.A. 1990. Fruit Growth and Development of 'Ideal' and 'Western' Pecans Carya illinoenis, endosperm development, cotyledon thickening, embryo growth, watery stage, gel stage, dough stage. J. Amer. Soc. Hort. Sci. 115:915-923. Hunter, J.H. 1956. What is happening to nitrogen, phosphate, and potassium in pecan orchard soils. Proc. Southeastern Pecan Growers Assoc. 49:44-47. Hunter, J.H. 1964. Time of applying nitrogen to pecan trees in sod. Proc. Southeastern Pecan Growers Assoc. 57:18-22. Hunter, J.H. 1966. Progress report with sprays of nitrate of potash on pecans. Proc. Southeastern Pecan Growers Assoc. 59:46-50. Hunter, J .H. 1967. Nitrate of potash sprays on pecans. Proc. Southeastern Pecan Growers Assoc. 60:101-104. Hunter, J.H. and H.E. Hammar. 1956. Relation of oil contents of pecan kernels to chemical components of leaves as a measure of nutrient status. Soil Sci. 82:261-269. Kays, S.J. 1977. Influence of the nut's internal oxygen partial pressure on the induction of pigmentation in the kernels of pecan. J. Amer. Soc. Hort. Sci. 102:531-533. Kays, S.J. and J.A. Payne. 1982. Analysis of physical and chemical parameters of the shells of pecan genotypes in reference to the production of phenolic plastics and resins. HortScience 17:978-980. Lewis, R.D. and J.H. Hunter. 1944. Changes In some mineral constituents of pecan nuts and their supporting shoots during development. J. Agr. Res. 68:299-306. McMeans, J.L. and H.M. Malstrom. 1982. Relationship between pecan yields and the quality and quantity of oil in nutmeats. HortScience 17:69-70. Pe' er, S. and Kessler, B. 1984. The development of the Delmas pecan fruit with special reference to growth phases and changes of lipids and potassium. Scientia Hortic. 24:323-329. Polles, S.G., B.W. Hanny, and A.J. Harvey. 1980. Condensed tannins in kernels of thirty-one pecan cultivars. J. Agric. Food Chem. 29:196-197. Sparks, D. 1975a. Concentration and content of 14 elements in fruit of pecan. HortScience 10:517-519. Sparks, D. 1975b. Nutrient concentration and content of pecan fruit. Annu. Rep. North. Nut. Grow. Assoc. 66:33-36. Thompson, T.E. 1982. Seasonal nut development pattern of 39 pecan clones. HortScience 17(3):494. Thor, C.B. and C.L. Smith. 1935. A physiological study of seasonal changes in the composition of the pecan during fruit development. J. Agric. Res. 50:97-121.

48 / Ray E. Worley

Wandruszka, c., A. Smith and S.l. Kays. 1980. The role of iron in pecan kernel color. Food Sci. Technol. 13(1): 38-39. Wells, 1.M. andl.L. McMeans. 1978. Rancidity, iodine values, and oil content of twentyone pecan cultivars. Proc. Southeastern Pecan Growers Assoc. 71:159-162. Wells, 1.M., 1.L. McMeans and 1.A. Payne. 1980. Pecan oil content and composition as affected by variety and orchard conditions. Proc. Southeastern Pecan Growers Assoc. 73:112-113. Wood, B.W. 1982a. Carbohydrates and fatty-acids in developing pecan fruit. J. Am. Soc. Hort. Sci. 107:47-50. Wood, B. W. 1982b. Gibberellin-like substances in developing fruits of pecan. HortScience 17:70--71. Wood, B.W. 1984. Free and bound abscisic acid and free gibberellin-like substances in pecan kernel tissues during seed development. J. Amer. Soc. Hort. Sci., 109:626--629. Wood, B.W. and C.C. Reilly. 1984. Pecan kernel proteins and their changes with kernel development. HortScience 19:661-663.

4 Pecan Processing Charles R. Santerre

Introduction The goal of food processing is to deliver a high quality product to the customer at an affordable price while at the same time, permitting a reasonable profit. The concept of quality is often ambiguous and generally determined at each sector of the pecan industry in different ways, often, with little regard to the consumer. For instance, quality to a producer is often measured in yield, size and absence of physical defects. Quality to a sheller is often measured in size, color, fill weight, and ability to crack and shell. Quality to a manufacturer, (i.e., ice cream manufacturer, baker, cereal manufacturer or confectioner) is often measured in size, color, absence of physical defects, absence of contaminants (Le., insects, shell fragments, illegal pesticides, pathogens, etc.) and absence of off-flavors. Quality to the consumer is often determined by flavor, texture, color, freedom from physical defects, freedom from contaminants, perception of wholesomeness, etc. Ironically, the producer may have the greatest influence upon the quality of pecans which reach the consumer but may pay the least attention to the attributes which are of greatest importance to the consumer. This is not to say that each step in the chain is of more or less importance in the maintenance of pecan quality. Each sector must pay special attention to the effects of handling on the final product. Stresses which occur in the orchard and at harvest may produce latent damage which is not detected until the final product has been manufactured. Some of the causes and manifestations of latent damage will be discussed in this chapter. At this point in our discussion, it is important to understand that raw pecans are living organisms which have a certain capacity to withstand stress. While drying can dramatically slow physiological processes, if enzymatic activity is not eliminated, chemical reactions can occur which may have a major effect on the quality of pecans during storage and handling. Some of these stresses are C. R. Santerre (ed.), Pecan Technology © Chapman & Hall, Inc. 1994


50 I Charles R. Santerre

unavoidable (i.e., cracking and shelling) while others are easily avoidable (i.e., excessive moisture, temperature abuse, etc.) during handling. It is the role of each segment of the pecan industry to understand the effects of handling on the final quality as perceived by the consumer. When we speak about quality in terms of growers and shellers, we can use the shell-out weight as a measure of an orchard's productivity. For instance, an orchard of one acre (0.4 ha) size yielding 100 pounds/tree (46 kg/tree) of inshell pecans with 50 pounds (23 kg) of shelled-out kernels has a lower yield than the same size orchard with a shell-out of 55 pounds (25 kg). So here we have a basis of quality for the grower which we can call harvest quality. It is a measure of productivity of an orchard and relates to the ease with which a sheller can shell the pecans. For the manufacturer who purchases those pecan kernels, it makes little difference what the productivity of the grower's orchard has been or how difficult the pecans were to shell. The manufacturer is interested in purchasing pecans based on amount and processor quality. Let's use a cookie manufacturer as an example. The cookie manufacturer will purchase pecans of a certain size based on their needs. Many manufacturers will buy the smaller size seedling pecans because it is more cost effective to put small pecans on pecan cookies than larger pecans. So for this cookie manufacturer, one aspect of quality relates to size. Finally, we should consider consumer quality. The consumer may not care about an orchard's productivity, shell-out ratio, or pecan size when eating a pecan cookie but may be mostly interested in the appearance (incl. color, surface appearance, etc.), aroma, texture and flavor. These latter parameters of quality may not even be considered by the grower as significant when the product is sold to the sheller or by the sheller when sold to the manufacturer. However, the manufacturer who is not concerned with those factors which determine consumer quality will soon be out of business. One common problem which is encountered in the trade of pecans between growers, shellers and manufacturers relates to the differences in perception of quality by each segment of the pecan industry. Growers do not understand the basis for the price paid by shellers, who in turn may not understand processor quality as it relates to a manufacturer's specifications and, finally, consumer acceptability. Now let us discuss the influence of processing on the quality of pecans while keeping in mind the end-user. A overview of pecan processing is given in a flowchart in Figure 4.1.

In-shell Pecan Processing The first goal of the grower should be to remove pecans as quickly as possible from the orchard floor. The primary reason being that by reducing moisture of in-shell pecans as quickly as possible, molding and rancidification will be avoided


t t Drying t Size Grading





t t Shelling t Size Grading












Color Sorting - - - - - - - - ,



Manual Sorting


- - - - - 1..

Color Sorting



Packaging .....__

t t Temperature Storage



Shipping Wholesale

Figure 4.1.


I ...


Flowchart of Processing Steps for Postharvest Handling of Pecans.


52 I Charles R. Santerre

or delayed. Heaton et al. (1977) studied the influence of moisture on recently harvested pecans. They spread nuts of five varieties on wet soil in a pecan orchard and made observations over a 10 day interval. Moisture increased from 20 to 55% for all varieties during the 10 days on the moist orchard floor. Molding was reported to increase from 30 to 87% in ten days and was directly related to moisture uptake. In a subsequent experiment, Heaton (1972) placed pecans from 15 varieties on Bermuda grass sod and pecan leaves which were laid on an orchard floor for five days during a late fall rain. Prior to being placed on the orchard floor, pecans were dried to 5 and 6% moisture and found to have 51.1 % 'sound' kernels. Moisture content following five days on the orchard floor, increased to an average 11.2% with a decrease in sound kernels to 43% while molding ranged from 7 to 35%. Pecans which were dried rapidly following harvest and prior to being placed on the orchard floor, had a higher percentage of sound kernels than pecans which were dried slowly. Additionally, pecan kernels which were maintained wet for several days, turned dark shortly after shelling and often had a bitter flavor. Therefore, maximum effort should be given to removing pecans promptly from the orchard floor to prevent molding and extend the shelf-life of stored pecans. Traditionally, pecans were left to dry on the tree and harvested exclusively from the orchard floor after shaking of smaller branches. Currently, mechanical shakers can effectively harvest pecans at an earlier date with the purpose of increasing nut yields and economic returns due to seasonal purchasing habits. Chinnan (1980) indicates that mechanically harvested pecans may have moisture levels as high as 30%. Therefore, drying in a quick manner is a priority for both mechanically-harvested pecans and pecans dried on the tree. Prior to drying, pecans should be separated from trash (incl. twigs, stones, leaves, pops, shrivels, and husks) in order to facilitate drying and reduce mold growth and pathogen transmission. The importance of pecan moisture dates back to early research (McCrory and Hurst 1929) which attempted to optimize drying temperature in order to preserve quality. Pecan kernels which are dried on the tree generally reach a moisture content of 8.0%. A rule of thumb in the pecan industry is to rapidly dry harvested pecans to below 4.5% (w.b.) moisture to preserve quality (Heaton et al. 1977). Optimal drying conditions were reported by McCrory and Hurst (1929), who indicated that drying temperatures greater than 38°C (100°F) adversely affect kernel color and flavor. Heaton et al. (1977) have provided information which is beneficial for determining the drying times based on temperature, relative humidity and air flow (Table 4.1). Chinnan (1980) determined the drying rate for 'Stuart' pecans at 34°C (95°F), 48% E.R.H. and airflow of 100 ftImin (32 m1min) to closely adhere to predicted values (Figure 4.2). Following harvest, expeditious drying at a temperature less than 38°C (100°F) will maintain optimal quality by preventing mold growth and maintaining light color. In-shell pecan drying will be discussed further in Chapter 5. In 1975, in-shell pecans represented approximately 9.6% of the total pecan sales (Powell, 1975). Standards for in-shell pecans were published by the USDA

Pecan Processing I 53 Table 4.1. Effect of Drying Conditions on Reduction of Kernel Moisture from 8.0% to 4.4% in In-Shell Pecans (adapted from Heaton et al. 1977). Temperature

Relative Humidity

Air Flow Rate

Drying Time

39°e (102°F) 25°e (78°F) 21°e (70°F) we (66°F) we (66°F) lOoe (50°F) ooe (32°F)

9 39 50 40 40 60 60

420 300 slight 640 0 slight slight

9 hr 17 hr 2-3 wk IS hr 2-3 wk 3-4 wk 4-6 wk

(1976) (7 CFR §51.1400-1415; 41F.R. 39303). These can be obtained through USDA-AMS; Fresh Products Branch, P.O. Box 96456, Rm. 2056 South, Washington, D.C., 20090 (ph. 202/447-2185). A color guide is available from Federated Pecan Growers' Association and can be obtained from the Georgia Pecan Growers' Association (18 Quail St., Leesburg, GA 31763). U.S. Grade No.1 and U.S. Grade No.2 were established based on shell color uniformity, shape,



12 .









CD ;:,

10 9




8 7








Time (hr) Figure 4.2.

Drying Profile of In-Shell Pecans (adapted from Chinnan, 1980).


54 I Charles R. Santerre

degree of damage, development, kernel color, and degree of damage. Following separation of in-shell pecans from trash, sorting by size is used to separate pecans into nine sizes: smaller than 9/16 in. (22 mm), 9/16 in. (22 mm), 10/16 in. (24 mm), 11116 in. (25 mm), 12/16 in. (26 mm), 13/16 in. (27 mm), 14/16 in. (28 mm), 15/16 in. (29 mm), and larger than 15/16 in. (29 mm) (Wagner, 1977). In-shell pecans may be sold as natural, bleached, dyed, waxed, and/or polished. In-shell pecans sold for the holiday trade are often bleached, dyed with a red or light brown food-grade dye, then waxed and polished to enhance their appearance. These pecans are popular especially during the holiday season as a gift item and are an economically significant product of the pecan industry. One problem often encountered during roadside trade of in-shell pecans is the fact that an outwardly acceptable pecan may contain an extremely rancid kernel which is not detected until the consumer is often miles away from the point of purchase. Roadside sales are often viewed as a method for great profit but, unfortunately, are often poorly regulated. In-shell pecans may be stored at these locations for months with no attempt to hold pecans at proper temperatures. While consumers don't always remember a good tasting product, one can be certain that a spoiled pecan will leave a long-lasting memory. The pecan industry would benefit from promotion of an identity between in-shell pecans and high quality which can be sold under a designated label. Following drying, in-shell pecans are often stored in temperature controlled facilities to delay and prevent mold development, insect damage, discoloration (darkening), absorption of volatiles (flavors), and rancidity. Harris (1960) indicated that mold development may result from inadequate drying or from storage in excessive humidity. Insect damage can occur if pecans are held at temperatures which permit insects to survive. Discoloration can occur by exposure to UV light, as a result of insect damage, as a result of early frost damage, by migration of pigments from shells and inner packing to kernels, or by oxidation of the iron-containing pigments in the testa (Kays, 1979). Absorption of volatiles occurs as a result of the high lipid content of pecans which acts as a sponge for lipophilic (lipid-loving) compounds. For example, storing pecans with climacteric fruit, such as apples, which produce a plant growth hormone called ethylene, will cause pecans to darken and have a shortened shelf life. In the past, cold storage units commonly used ammonia as the refrigerant. Leakage of ammonia in pecan storage chambers causes pecans to darken rapidly. Ammonia refrigeration units have mostly been replaced by systems which are less dangerous to operate, however, reduction in Freon usage due to environmental concerns for ozonedamage may return ammonia to use as a refrigerant. Rancidity occurs by oxidative reactions which adversely affect the flavor of pecans. Storage temperature is directly related to rancid flavor development and storage of pecans at low temperatures will delay these oxidative changes. Woodroof and Heaton (1967) indicated that in-shell pecans can be stored for six months at 22°C (70°F), for nine months at 8°C (47°F), for 18 months at 0 to

Pecan Processing I 55

3°C (32 to 36°F), for 30 months at -6 to -4°C (20 to 25°F), and for six to 10 years at -18°C (O°F), without "appreciable loss of quality." In comparison, shelled pecans can be stored for three to four months at 22°C (70°F), for six months at 8°C (47°F), for 12 months at 0 to 3°C (32 to 36°F), for 18 to 24 months at -6 to -4°C (20 to 25°F), and for six to 10 years at -18°C (O°F). It is apparent from several studies (Woodroof and Heaton 1962; Wagner 1980; Nelson, Senter and Forbus 1985), that pecan kernels are more stable when maintained in-shell. Unfortunately, the additional volume of in-shell pecans makes long term storage less practical than storage of kernels. Shellers should attempt to maintain pecans under controlled conditions and in-the-shell as long as possible to maintain desirable flavor characteristics. Removal of pecans from cold storage must be controlled to prevent moisture from the surrounding atmosphere from condensing on pecans and significantly increasing pecan moisture to a point where molding may occur. Pecans which are stored at sub-freezing temperatures are brittle and susceptible to mechanical damage. Pecans removed from frozen storage should be brought to room temperature in conditioning rooms which are maintained at low relative humidity. A series of rooms with proper air flow and humidity should be temperature adjusted to 5 and 16°C (40 and 60°F) and pecans should be placed in these rooms sequentially for several days to prevent condensation. Pecans from frozen storage should be conditioned for about five to seven days prior to handling at ambient temperatures.

Shelled Pecan Processing In 1975, over 90% of pecans were shelled prior to sale (Powell 1975). Standards for shelled pecans were published by the USDA (1969) (7 CFR §51.1400-1415). Due to the fact that pecans have a longer shelf-life in the shell (Nelson, Senter and Forbus 1985) and that most shellers do not have the equipment to shell an entire year's crop instantly, pecans are often stored in-shell and removed from cold storage to be shelled as required by purchase orders. Prior to cold storage, in-shell pecans are graded by size. Sorting by size is important in order to adjust shelling equipment for optimal shelling efficiency to obtain minimal kernel breakage. In-shell pecans which are removed from cold storage, which is less than O°C (32~ are brittle and should be brought to ambient temperatures as previously described. Another procedure which is applied prior to shelling, in order to reduce kernel breakage and improve shelling efficiency, is conditioning. Conditioning, prior to shelling, involves adding moisture to the pecan kernel. Moisture is absorbed through the vascular system at the base and apex and passes through the middle partition to the kernel. Kernel moisture generally rises from about 4% to about 8% which increases pliability and reduces kernel shatter during cracking. Conditioning can be done by moisture equilibration in a humidity-

56 / Charles R. Santerre

controlled storage room, by cold water soaking, by hot water soaking, or by steam processing. Cold water soaking is done by holding pecans in 1000 ppm chlorinated water for one to two hours and then holding for 12 to 24 hours prior to cracking (Forbus and Senter 1976). One difficulty with the chlorine soak involves maintaining the chlorine concentration within GMP (Good Manufacturing Practices) levels. Hot water soaking is done by holding pecans for three to five minutes in 86°C (187°F) water then holding pecans for 12 to 24 hours before cracking. Steam processing is done with a three to four minute steam (38°C; 100°F) treatment. Each of these conditioning processes, with the exception of humidity-controlled storage, can be used to sanitize pecans and reduce insects and pathogens. The U.S. Food and Drug Administration requires some treatment to destroy E. coli bacteria which may be present. Pecan sanitation will be discussed further in Chapter 6. Dielectric heating has been proposed as an alternative heating method (Senter et al. 1984a & b). Dielectric heating involves placing pecans between parallel-plate electrodes attached to a dielectric heater which is operated at 43MHz and which exposes pecans for one to three minutes. Pecans which were dielectric ally heated to an internal temperature between 88 and 156°C (190 and 313°F) were superior to steam heated pecans in color during storage. Dielectric heating may also offer a method for inactivating enzymes in the pecan which may cause rancid flavor to develop (Senter et al. 1984a). In a comparison of conditioning processes, Forbus and Senter (1976) found that atmospheric pressure steam processing for three minutes produced more intact halves which were less susceptible to breakage following shelling than pecans treated with the cold water soaking or the hot water soaking methods. Senter et al. (1984b) indicated that steam processing raised kernel temperature to 93°C (200°F) which caused kernel darkening that was later reversed during storage. Steam processing has been shown to produce a 12-17% increase in undamaged halves following shelling when compared to cold- or hot-water soaking methods, which give 50-87% intact kernels (Forbus and Senter 1976). Following proper conditioning, cracking is performed. The two commonly used crackers in commercial operations today are the Meyer Machine Co. Cracker and the Quantz Rotary Nutcracker. These will be discussed further in Chapter 5. For the Meyer Machine Co. Cracker, the pecans are dumped into a hopper and fed to a rotating feed wheel which orients nuts to receive an impulse force conveyed through plungers striking at each end of the pecan simultaneously (Forbus and Senter 1976). Unlike the Meyer Cracker which has been the industry standard cracker for 60 years, the Quantz cracker has a throughput of 600 to 950 nuts per minute (as opposed to 86 nuts per minute for the Meyer Cracker), requires no pecan conditioning (may even require drying) and requires no size sorting of in-shell pecans (Cabaniss, 1982). The Quantz cracker was developed in the early 1980s, by James Bland Quantz and promises 80 to 85% intact halves following cracking which is comparable to the Meyer Cracker, however, the Quantz cracker is considerably more expensive. It is

Pecan Processing / 57

desirable to produce more intact halves following cracking and shelling in order to reduce the pecan piece processing which is necessary for removal of shell pieces and weevil larvae. Shelling plants generally size pecans prior to cracking and, in this manner, can adjust the Meyer cracker plunger's length-of-stroke for optimal efficiency for each size shell. The Quantz Rotary nutcracker self-adjusts to accommodate pecan size variations. The cracked kernel, with shell and inner packing, is dumped through a discharge chute for the shelling operation. Shelling, or removal of shells and inner packing from kernels, is the next processing operation. Cracked nuts are conveyed into a sheller which can be a rotating drum consisting of cylindrical rings spaced to assist the separation. As product traverses the rotating ringed cylinder, it is agitated to facilitate the separation by metal shafts which protrude from the center axis. The separated debris and kernels, are discharged and sized through vibrating screens which separate intact kernels into eight sizes (Table 8.3). Pecan shelling also generates pecan pieces which have value if they are cleaned of shell fragments, inner packing, weevil larvae, and dark color pieces. Following the shelling operation, previously conditioned pecan kernels have approximately 8% moisture and must be dried. In addition, whole kernels must be sorted for insect damage and to separate remaining shells. Whole kernels can easily be separated from pecan weevil larvae by sizing operations, however, kernels pieces shattered during cracking and shelling may be difficult to separate by size from the larvae. For cleaning of pecans, a combination of methods are often employed. Premium, whole kernels are generally sorted by hand, by color sorting machines, and by screening as previously mentioned. Color sorting separates pecans into eight color grades. Pecan kernel color grades include light, light amber, amber, dark amber, golden, light brown, medium brown, and dark brown. Pieces are sorted by size (Table 8.4), then cleaned by electronic color sorting, manual picking tables and, in some cases, by vibrating tables and/or flotation in an alcohol/water bath. Due to the fact that some pieces are the same size as pecan weevil larvae and that tungsten-light electronic color sorting is not a useful means of separation, pieces are often separated by manual sorting under UV lamps. Pecan weevil larvae are lighter than pieces when viewed under UV light. Hand sorting is slow, expensive and yields approximately 20 lbs (9 kg) of pieces per hr. Electronic color sorting yields approximately 60 lbs (27 kg) per hr and can be operated 24 hrs per day, however, pecan weevil larvae cannot be sorted from pecans with existing color sorting equipment designs. Further research is necessary to determine if minor modifications to existing sorting equipment can successfully sort based upon reflectance differences between weevil larvae and pecan pieces at a selected wavelength. Another strategy for providing customers with pecans which are free of shell fragments and pecan weevil larvae is to chop pecan halves. Halves are easy to sort (because of size differences) from undesirable components. Efficient chopping

58 / Charles R. Santerre

requires that pecans be dry enough to prevent gumming of the chopper and wet enough so that excessive meal is not produced during chopping and sorting and sizing operations. A moisture of 4% is recommended as a starting point for optimizing the pecan moisture to achieve optimal chopping efficiency. An effective chopping operation will generate 3 to 6% pecan meal which is a difficult commodity to sell due to low market demand. Optimal chopping is dependent upon pecan moisture and rotation speed of the chopper. Chopping is also used to produce pecan pieces which are in higher demand by manufacturers. Alcohol flotation is used to separate pecan weevil larvae from pecan pieces due to buoyancy differences. The pecans and weevil larvae are floated in an ethanol/water solution where pecan pieces sink and weevil larvae float and are then skimmed from the surface. Unfortunately, pecan weevil larvae will sink if they have any holes in their skin. Pecan pieces are then removed from the bath and dried. This technique is limited by undesirable flavors which are imparted to the pecans from the alcohol and by yearly fluctuations in the buoyancy of either pecan pieces or weevil larvae which limits the efficiency of this process. This process is expensive and can be cost prohibitive for processors. Attempts have also been made to separate weevil larvae from pieces by passing pecans and larvae through an electrostatic separator. This procedure has met with only limited success as a commercially viable process. It is important to reduce pecan moisture as quickly as possible following shelling. Kernels conditioned prior to shelling or floated in an alcohol/water bath contain about 8% moisture and must be dried to 3.0-4.0% moisture to maintain consumer quality. Drying below 2% may cause pecans to develop surface cracks which increases brittleness and permits oxygen to enter into the inner matrix and initiate oxidation. Excessive drying causes some lipids to migrate to the surface of the nut and these lipids may be less stable to oxidative processes than membrane bound lipids or bulk lipids in vacuoles. The end results would be observed as shortened pecan shelf-life due to accelerated rancid flavor development. Heaton et al. (1977) reported that 'Stuart' pecans dried above 26°C (80 P), from a moisture of 7.49% to a moisture of 2.6-4.2%, had a lower quality score than pecans dried for longer intervals below 26°C (800 P). Pecans dried above 49°C (120 P) had increased surface oil and a lower quality score following six months of storage than pecans dried at less than 49°C (1200 P). Drying at 26°C (80 0 P), 38°C (lOO°F), 49°C (120 0 P) and 60°C (1400 P) required 15,2.75, 1.75 and 1.25 hours, respectively. Commercial operators, who require sufficient throughput may incorporate heated, forced-air dryers to achieve a drying temperature of 49°C (1200 P) for pecan drying. Pecans can also be dried by holding at -12°C (15°P) and 45% equilibrium relative humidity (ERH) for up to two months (Heaton and Woodroof 1970). 'Curtis' and 'Van Deman' kernels reached 3.8% moisture (from 7.4%) in 15 days when stored at -12°C (15°P) and 45% ERH (Heaton et al. 1977). Because pecans can become brittle at -12°C (15°P) and 45% ERH, the recommended temperature for storage is O°C (32°P) and the effects 0


Pecan Processing / 59 Table 4.2. Influence of Equilibrium (ERH) Relative Humidity and Storage Temperature on Weight Loss in Pecans (adapted from Heaton and Woodroof, 1970) Percent weight change for pecans stored at ooe (32°F)

ERH 41% -0.05 -0.50 -0.60 -0.65 -0.70

ERH 51%

ERH 65%

ERH 72%

Time (weeks)

+0.35 +0.10 +0.10 0 -0.15

+0.45 +0.35 +0.55 +0.55 +0.60

+0.75 +0.95 +1.15 +1.13 +1.45

2 3 4.5 7

Percent weight change for pecans stored at 10°C (50°F)

ERH 39% -0.80 -0.65 -0.45 -1.05 -1.05

ERH 50%

ERH 65%

ERH 72%

Time (weeks)

-0.20 -0.20 -0.20 -0.45 -0.45

+0.55 +0.65 +0.85 +0.85 +0.85

+0.85 +1.30 +1.45 +1.35 +1.40

1 2 3 4.5 7

Percent weight change for pecans stored at 200e (68°F)

ERH 35% -0.80 -1.10 -1.10 -1.10 -1.50

ERH 50%

ERH 65%

ERH 73%

Time (weeks)

-0.10 -0.25 -0.20 -0.60 -0.50

+0.40 +0.30 +0.30 +0.25 +0.20

+1.20 +1.15 +1.55 +1.40 +1.40

1 2 3 4.5 7

of ERH on weight change can be determined for selected temperatures by data given in Table 4.2 (Heaton and Woodroof 1970). While moisture measurement is the most common means for determining water content in pecans in order to prevent molding, Beuchat (1980) recommends that water activity (llw) be used instead of moisture measurements. Water activity is a measure of free water which is available to support biological and chemical reactions. Molds and bacteria have a minimum water activity necessary to support their growth. Drying of pecans, or dehydration, is intended to reduce the water activity of pecans so that organisms will not proliferate. Water activity is the ratio of vapor pressure of the system (P) to the vapor pressure of pure water (Po):

llw = P/Po equilibrium relative humidity (ERH)

= llw * 100

Beuchat (1980) indicates that the moisture of pecans is inversely proportional with lipid content. Lipid content is often dependent upon degree of maturity of

60 / Charles R. Santerre

the pecan and generally ranges from 60% to 77%. Pecans containing 64% lipid and 5.7% moisture may have a water activity (llw) = 0.68 at 21°C (70°F) , whereas, pecans containing 70% lipid and 4.5% moisture may have the same water activity. Pecans having an llw < 0.68 will not support the growth of mold or bacteria, and may have a moisture content from 4.5 to 5.7%, depending upon the lipid composition. It is for this reason that some researchers report that pecans will mold above 5% moisture, whereas, other researchers claim that pecans will only mold above 7 or 8% moisture. Few studies have examined the quality of pecans from wholesale or retail distributors. Williams, La Plante and Heaton (1973) sampled shelled pecans from retail stores in six cities and evaluated for pecan quality using USDA grading criteria. Of the samples examined 50.6% failed to qualify as U.S. No. 1 grade as a result of poor kernel fill, rancidity, dark color, and/or excessive pieces. Rancid flavor was found in 16.8% of samples. The high level ofrancidity is not surprising if one considers the fact that pecan kernels sold from grocery stores are held on store shelves at room temperature and often long past their shelf-life. It has been mentioned that pecans contain around 70% lipid, of which, 90% is unsaturated. Given that pecans are composed of highly oxidizable lipids, it is surprising that they can be stable from rancid flavor development when stored at room temperature for as long as four to six months. Actually, the pecan is more stable than free oil and possesses mechanisms to resist oxidation. This can be demonstrated by observing the oxidation of pure pecan oil. Pyriadi and Mason (1968) reported that TBA and peroxide values (measures of oxidation) increased dramatically over 14 days of holding at 60°C (140°F) and in lighted conditions with available oxygen. Pecan kernels held under these same conditions would have accelerated oxidation but significantly lower TBA and peroxide values than free oil. Pyriadi and Mason (1968) did find a positive correlation between tocopherol content (a naturally occurring antioxidant) and oil stability. Other researchers have reported that phospholipids found in the membrane of pecan cells playa role in lipid oxidation. Storage stability of pecans has never been demonstrated to be directly correlated with the amount of unsaturated fatty acids in the kernel. Other factors, such as concentration of tocopherols and phospholipids, membrane stability, availability of oxygen and light, and storage conditions must also be considered. In the following discussion, we will investigate many factors which influence the storage stability of pecan kernels. It is logical to assume that eventually a correlation will be found between storage stability of pecan kernels and variety. Due to the many factors which must be accounted for and seasonal or yearly variations, there is only limited data on the influence of variety on the shelf-life of pecans. Senter and Forbus (1979) demonstrated varietal differences for the rate of rancidification when kernels of three varieties were stored at 30°C (86°F) for 24 weeks. The time of harvest is one factor which influences pecan shelf-life. Heaton,

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Worthington and Shewfelt (1975) demonstrated that early harvested pecans had a pungent flavor at harvest but when properly dried, the pungent flavor gradually declined and the shelf-life of these pecans was superior to traditionally harvested pecans. Resurreccion and Heaton (1987) demonstrated that early harvested pecans had better color and consumer acceptability than traditionally harvested pecans. Early harvested pecans also have the advantage of being available to wholesale and retail markets when the price is highest. Shelling has been demonstrated to reduce the shelf-life of pecans. Woodroof and Heaton (1967) indicated that in-shell pecans can be stored for six months at 22°C (70°F), whereas, shelled pecans will store for only three to four months at this temperature. Kays and Wilson (l978a&b) attempted to correlate color changes in the testa (skin) with varietal differences and shelling. They measured the color changes of eight cultivars plus one selection during storage and found that 'Stuart', 'Cherokee', '48-15-3' and 'Caddo' pecans had less darkening when stored in-shell than when stored shelled. 'Schley,' 'Desirable,' 'Mohawk' and 'Shawnee' darkened at the same rate whether stored shelled or in-shell. By far, controlling storage temperature is the single most important strategy for extending the shelf-life of shelled or in-shell pecans. Hao, Heaton and Beuchat (1989) reported that pecans could be stored for 25 years when held at -20°C (-4°F). Pecans were stored under ambient air conditions in hermetically sealed containers and, when organoleptically evaluated, had characteristics of color, flavor and appearance which were not different from freshly harvested pecans. While refrigeration or freezing are acceptable strategies for extending shelf-life of pecans in some products, it is not an acceptable approach for products which are stored at room temperature and which require a six to 12 month shelf-life, such as cookies or breakfast cereals. Clearly other strategies for extending the shelf-life of pecans are necessary if products stored at ambient temperatures are to be successfully marketed. Moisture is possibly the second most important factor which must be regulated in order to extend the storage-life of pecans. In-shell pecans may darken from excessive moisture due to tannin migration from the shell lining to the kernel (Wagner 1980). Williams, La Plante and Heaton (1973) found a wide range of moisture levels in pecan kernels collected from retail shelves. Pecan moistures ranged from 2.3% to 6.4% with an average of 3.4% moisture for raw pecans. As previously mentioned llw plays a crucial role in mold growth which can dramatically affect pecan shelf-life. Beaudry, Payne and Kays (1985) found a positive correlation between moisture content and respiration rate (which was measured as carbon dioxide produced). Higher respiration was found for shelled pecans than for in-shell pecans which may explain the reduced shelf-life of shelled kernels. On the other hand, excessively low moisture may lead to changes in membrane stability which causes lipids to leak from cells or by structural changes which may cause cracks in the surface of the pecan and increase the exposure of oxidation-sensitive lipids to oxygen. Excessively low llw causes

62 / Charles R. Santerre

pecans to be susceptible to breakage during shipping and handling (Beaudry, Payne and Kays 1985). Another factor which may shorten the shelf-life of stored pecans is exposure to sunlight. Pecans are commonly sold in packages which permit consumers to see the product. Heaton and Shew felt (1976) exposed pecans to sunlight for various intervals up to 24 hours. There was a significant (p = 0.01) darkening from four hours of sunlight exposure and lightness was reduced 21 % following 24 hours of exposure. Pecans exposed to cool white fluorescent light were darkened significantly less (p = 0.05) than pecans exposed to sunlight. This is most likely due to the lower intensity and narrower spectrum of ultraviolet light from the cool white fluorescent source. Heaton and Shewfelt (1976) demonstrated no differences in darkening when pecans were stored for 24 weeks at 23°C (73°F) under cool white lights in flexible pouches which had lower light transmission rates than pouches with higher light transmission rates. In addition to changes which occur in the light-induced darkening of the testa, initiation oflipid oxidation may be an effect of UV light exposed pecans. Enzyme inactivation has been investigated as a means of extending the shelflife of pecans. Wells (1951) indicated that enzymes present in pecans are inactivated by heating to an internal temperature of 82.2°C for three minutes. Abd EI-Wahab et al. (1984) heated pecans to 160 or 180°C (320 or 356°F) for five to 15 minutes prior to storage at room temperature. They reported that heat inactivation of enzymes reduced the peroxide value (a measure of oxidation) of pecans stored at room temperature, however, the pecans which had been heat treated had higher peroxide values than cold stored pecans. Changa, Matta and Silva (1988) investigated the influence of ionizing radiation on the shelf-life of shelled pecans. They irradiated frozen pecans with 0.1 to 1 kGy then held pecans at 26°C (79°F) for four months. Although they found that irradiation was effective for reducing Aspergillus spp. organisms, it was not effective for extending pecan shelf-life by reducing oxidative changes. Roasting of pecans is a common processing method which inactivates enzymes. However, roasting causes excessive drying of the pecan which increases surface oil. It is believed that the increase in surface oil (which is exposed to oxygen) along with thermal destruction of naturally antioxidants (such as tocopherols) causes roasted pecans to have a significantly shorter shelf-life than raw pecans. Roasted pecans have a characteristic flavor which is caused by a wide range of compounds including pyrazines which are also produced during the baking of bread. Numerous treatments have been investigated to reduce or delay rancid flavor development of pecans stored at ambient temperatures. Several strategies have focused on attempting to regulate the concentration of oxygen which pecans are exposed to during storage. Reduction in oxygen can be accomplished by packaging in vacuum, nitrogen, carbon dioxide, by adding an oxygen absorbing com-

Pecan Processing / 63

pound to the package, or by applying edible coatings to the pecans which provides a semi-permeable oxygen barrier. First, recall that pecans are living organisms which are capable of biochemical reactions including respiration. Pecans which have not been treated sufficiently to inactivate their respiratory enzymes (i.e., either by heat or irradiation) require some oxygen to remain in aerobic balance. Respiring pecans which are placed in a very low oxygen environment (i.e., less than 2%) will undergo anaerobic respiration and deteriorate. Santerre, Scouten and Chinnan (1990) stored pecans at 38°C (100°F) in oxygen impermeable bags with an oxygen absorbing compound in order to determine the affects of low oxygen environments on quality. Oxygen concentrations in the bags were 1.6% and caused a 'fruity' flavor to develop by 52 days of storage. In addition, pecan flesh color was darkened and texture was softened by 43 days of storage. This finding was supported by Dull and Kays (1988) who reported a slightly 'acid' flavor from pecans which were stored in oxygen impermeable foil pouches for 24 weeks. They suggested that packaging materials with O2 transmission rates above 0.08 cc O2 100 cm -1 24 hr -1 be selected for storage of pecans. It remains to be demonstrated whether, for a given storage temperature and pecans water activity, the oxygen concentration to permit aerobic respiration is greater than or less than the oxygen concentration which is necessary for lipid oxidation. Storage of nuts in cans under vacuum has long been a practice of the snack food industry. Ahmed and Storey (1976) reported that vacuum packed pecans which were stored at 21°C (70°F) had a significant loss of quality by six months. Harris (1960) reports that pecans dried in a 107°C (225°F) oven to 1.6% moisture and packaged in glass jars by the 'hot-pack' process were edible after seven years in ambient storage. Due to the heating treatment used by Harris, these pecans more closely resembled roasted rather than raw nuts. Vacuum packaging in cans is often not the method of choice due to the cost of producing a product in an evacuated can. Further research is necessary to determine if packaging in a vacuum environment is beneficial for extending the shelf-life of raw pecans. Nitrogen flushing can be used to reduce oxygen concentration in packaged pecans. Sacharow (1971) suggests that nitrogen be used instead of carbon dioxide due to absorption of the later by pecans. A nitrogen flush system should reduce the oxygen concentration to 2-3% for optimal storage conditions. Dull and Kays (1985) indicate that nitrogen flushing is commonly used to achieve an oxygen concentration below 5%. Incorporation of purge and flush packaging equipment into a commercial processing plant is expensive both from the equipment cost and the package materials cost. Edible coastings (films) may provide another means for extending pecan shelflife. Edible coatings are applied to pecans by either dipping or spraying then drying to form a barrier to oxygen, carbon dioxide, water vapor and/or physical abrasions. Godkin, Beattie and Cathcart (1951) dipped pecan kernels in a 40%

64 / Charles R. Santerre

sucrose-based syrup and observed a delay in rancidity of six weeks when treated pecans were compared to untreated pecans when both were stored at 45°C (113°F). Senter and Forbus (1979) coated pecan kernels with acetylated monoglycerides and reported only marginal benefit from the edible coating for delaying rancidity. They found that variety played a great role in storage stability than did the edible film. Santerre, Scouten and Chinnan (1990) found dramatically increased 'fruity' flavor during storage for pecans which were previously dipped in a sucrose polyester mixture. Their results may have been due to anaerobic respiration resulting from very low oxygen transmission across the edible film. Edible coatings are playing a greater role in the food industry for extending the shelflife of foods by stabilizing the Ilw, flavor, color, and physical integrity of foods. This up-and-coming technology needs further study as a potential means for extending the shelf-life of pecans stored at ambient temperatures and in complex food matrices. Another treatment which has demonstrated only limited success in attempts to extend pecan shelf-life, is coating of pecans with antioxidants. Godkin, Beattie and Cathcart (1951) attempted to incorporate the antioxidants alpha, beta, and gamma tocopherol (vitamin E), ascorbic acid (vitamin C), or NDGA (nordihydroguaiaretic acid) in a 40% sucrose-based syrup edible coating in order to extend the shelf-life of pecans stored at 45°C (113°F). They found no benefit from the antioxidants for delaying rancidity over and above the six weeks of additional shelf-life attributed to the sucrose syrup. Changa, Matta and Silva (1988) sprayed pecans with 0.02% Tenox 20A and found a significant increase in peroxide values for pecans stored zero, four and eight months. The significant increase in peroxide values for pecans stored for zero months did not correlate with flavor ratings and was possibly due to interferences with the peroxide value measurements. Sensory scores for the pecans treated with the antioxidant and stored for eight months were better than untreated pecans but not statistically different (p = 0.01). Senter and Forbus (1979) added Tenox 20 (0.02% of lipid content) to acetylated monoglycerides which were applied as an edible coating to kernels. They found only marginal improvements in the peroxide value measurements with the addition of antioxidants to the monoacyl glyceride coating mixture. Antioxidants are widely used in the pecan industry to extend shelf-life, however, published data is inconclusive regarding the benefits of antioxidant treatment for extending the storage stability of pecans. Many attempts have been made to extend the shelf-life of semi-perishable pecans which are considered by many to be the 'Cadillac' of nuts. Successful market expansion by the pecans industry will depend upon efforts to produce a dependable year-round supply of high quality nuts which can be used in new food applications including those foods which are stored at room temperature. A concerted effort by producers and processors will achieve this goal and ensure economic viability of the pecans industry into the 21 st century.

Pecan Processing / 65

References Abd EI-Wahab F.K., A.M. EI-Hamady, S.M. EI-Nabawy, A.M. Rawash, and L.F. Hagagg. 1984. Effect of storage and prestorage treatments on pecan fruit decay and oil properties. Gartenbauwissenchaft. 49(2):61-64. Ahmed, H.S., J.B. Storey. 1976. Effect of storage period on the quality of pecan kernels kept under vacuum. Lybian Journal of Agriculture. 5:83. Beaudry, R.M., J .A. Payne, and S.J. Kays. 1985. Variation in the respiration of harvested pecans due to genotype and kernel moisture level. HortScience. 20(4):752-754. Beuchat, L.R., and E.K. Heaton. 1980. Factors influencing fungal quality of pecans stored at refrigerated temperatures. Journal of Food Science. 45:251-254. Cabaniss, D. 1982. Industry's 'better mousetrap' born in South Carolina garage. Pecan South. 15(6):5-10. Changa, T., F.B. Matta, and J. Silva. 1988. Pecan kernel quality as affected by an antioxidant and irradiation. Proceedings of S.E. Pecan Growers Association. 81:5963. Chinnan, M. S. 1980. Concept of single-layer drying of pecans in modeling energy efficient drying systems. Pecan Quarterly. 7(5):14-15, 17-19. Dull, G.G., and J. Kays. 1988. Quality and mechanical stability of pecan kernels with different packaging protocols. Journal of Food Science. 53(2):565-567. Forbus, Jr., W.R., and S.D. Senter. 1976. Conditioning pecans with steam to improve shell efficiency and storage stability. Journal of Food Science. 41:794-798. Godkin, W.J., H.G. Beattie, and W.H. Cathcart. 1951. Retardation ofrancidity in pecans. Journal of Food Technology. 5:442-447. Hao, D.Y., E.K. Heaton, and L.R. Beauchat. 1989. Microbial, compositional, and other quality characteristics of pecan kernels stored at -20 degrees C for twenty-five years. Journal of Food Science. 54(2):472-474. Harris, H. 1960. Processing and storage of shelled pecans. Auburn University, Agricultural Experiment Station. 53:55, 57-59, 62-63. Heaton, E. K. 1972. Moisture and molding of pecans. Proceedings of S .E. Pecan Growers Association. Heaton, E.K. and A.L. ShewfeIt. 1976. Pecan quality effect of light exposure on kernel color and flavor. Lebensm.-Wiss. u.-Technol. 9:201-206. Heaton, E.K., A.L. ShewfeIt, A.E. Badenhop, and L.R. Beuchat. 1977. Pecans: handling, storage, processing and utilization. University of Georgia, Agricultural Experiment Station. Research Bulletin 197:79. Heaton, E.K., and J.G. Woodroof. 1970. Humidity and weight loss in cold stored pecans. Amer. Soc. Heating Ref. Eng. 12(4):49-51. Heaton, E.K., R.E. Worthington, and A.L. ShewfeIt. 1975. Pecan nut quality. Effect of time of harvest on composition, sensory and quality characteristics. Journal of Food Science. 40: 1260-1263.

66 I Charles R. Santerre

Kays, S.J.,and D.M. Wilson. 1978a. Genotype variation in pecan kernel color and color stability during storage. Journal of Amer. Soc. Hort. Sci. 103(1):137-141. Kays, S.J., and D.M. Wilson. 1978b. Varietal differences in pecan kernel color at harvest and during storage. Pecan South. 5(1):18-19. Kays, S.J. 1979. Pecan kernel color changes during maturation, harvest, storage and distribution. The Pecan Quarterly. 13(3):4-12, 34. McCrory, S.H., and W.H. Hurst. 1929. Pecan Drying. National Pecan Association. Nelson, S.O., S.D. Senter, and W.R. Forbus Jr. 1985. Dielectric and steam heating treatment for quality maintenance in stored pecans. J. Microwave Power. 1985:7174. Powell, J.V. 1975. Competition in marketing domestic tree nuts. Pecan South 2:198202,209. Pyriadi, T.M., and M.E. Mason. 1968. Composition and stability of pecan oils. Journal of the American Oil Chemists Society. 45(6):437-440. Resurrection, A. V.A. and E.K. Heaton. 1987. Sensory and objective measures of quality of early harvested and traditionally harvested pecans . Journal ofFood Science. 52: 10381058. Sacharow, S. 1971. Packaging confections and nutmeats. Food Product Development. 5(1):78, 80, 82. Santerre, C.S., AJ. Scouten, and M.S. Chinnan. 1990. Room temperature of shelled pecans: Control of oxygen. Presented at the 83rd Annual convention of the Southeastern Pecan Growers Association. Destin, FL: 113-121. Senter, S.D., and W.R. Forbus Jr. 1979. Effects of acetylated monoglyceride coatings on pecan kernel shelf-life. Journal of Food Science. 44:1752-1755. Senter, S.D., W.R. Forbus Jr., S.O. Nelson, R.L. Wilson Jr., and R.J. Horvat. 1984a. Effects of dielectric and steam heating treatments of the storage stability of pecan kernels. Journal offood Science. 49:893-895. Senter, S.D., W.R. Forbus Jr., S.O. Nelson, R.L. Wilson Jr., and R.J. Horvat. 1984b. Effects of dielectric and steam heating treatments on the pre-storage and storage color characteristics of pecan kernels. Journal of Food Science. 49(6):1532-1534. Wagner, A. 1980. Pecan storage an important post-harvest practice in preventing nut damage. Pecan South. 7(5):40-43. Wagner, A. 1977. A review of factors affecting shell-life of stored pecans. The Pecan Quarterly. 11(2):14-15. Wells, A.W. 1951. The storage of edible nuts. USDA Agr. Res. Adm. Bur. Plant Ind., Soils and Agr. Eng. Report No. 240. Williams, F.W., M.G. LaPlante, and E.K. Heaton. 1973. Evaluation of quality of pecans in retail markets. Journal of Amer. Soc. Hort. Sci. 98(5):460-462. Woodroof, J.G., and E.K. Heaton. 1967. Controlling quality in pecans. The Peanut Journal and Nut World. XLVI(6).

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Woodroof, J.G., and E.K. Heaton. 1962. Storage of pecans. University of Georgia, Agricultural Experiment Station. Mimeograph Series N.S. 149. United States Department of Agriculture. 1969. United States standards for grades of shelled pecans. 7 CFR 51.1400-1415. United States Department of Agriculture. 1976. United States standards for grades of pecans in-shell. 7 CFR 51.1400-1415.

5 Mechanization of Post-Harvest Pecan Processing Kevin A. Sims

The mechanization of pecan processing, including harvesting, cracking and shelling, is a relatively recent advancement when compared to other mechanized food processing systems. The equipment for sizing, separating, cracking, drying and packaging of pecans has only been developed since the early 1920s (Woodroof and Heaton 1961). An overview of pecan harvesting is presented in Chapter 2. Chapter 4 provides the pecan processor with the requirements necessary to maintain product quality throughout the entire processing, handling and storage of pecans. In this chapter, post-harvest pecan processing equipment will be discussed. Post-harvest pecan processing, or "shelling" as it is called in the pecan industry, encompasses the following operations; secondary cleaning, in-shell size sorting, conditioning of the nuts, cracking, shelling, separating the meat from the shell, sorting of the meats based on size, dryness, and color of the meats, packaging and storage. Each of these operations will be described below in terms of the more common equipment used to accomplish each step in post-harvest pecan processing. Much of the information presented here has been obtained from equipment manufacturers' product bulletins and catalogs. Although several companies provided literature regarding their specific equipment, no attempt has been made to summarize each company's processing equipment which is available to pecan shellers. In addition, the mention of company names is not to be construed as an endorsement of that company's equipment or products.

Pecan Cleaning, Grading and In-shell Sizing As harvested pecans arrive at a shelling plant, they undergo additional cleaning to remove any foreign material, e.g., twigs, leaves, stones, hulls and pops, that were not removed in the orchard at the time of collection. Small twigs or sticks are removed using either a "rodding" machine or by C. R. Santerre (ed.), Pecan Technology © Chapman & Hall, Inc. 1994


Mechanization of Post-Harvest Pecan Processing / 69

passing the pecans and twigs over an open chain link belt. Rodding machines consist of a cylindrical cage with rods attached to the outside. As the cage rotates, sticks are picked up and deposited separately from the pecans (Woodroof 1979). As one may expect with the open chain link belt, twigs and sticks are retained on the belt as the pecans and smaller debris fall through the openings. After removing the sticks and other large debris, the next cleaning operation involves the removal of pops, culls, shrivels and leaves. This is accomplished using an adjustable vacuum and taking advantage of the density difference that exists between the good quality edible nuts and the lesser quality pops, shrivels and trash. The vacuum level is adjusted by controlling the height of the nozzle above the belt. Prior to sizing, broken and unhulled nuts should also be removed. Proper inshell nut sizing is critical to obtain maximize production of pecan meat halves during subsequent cracking and shelling operations. There are several types of nut graders manufactured by Meyer Machine Company (San Antonio, TX). Production capacity ranges from approximately 600 to 10,000 lbs/hr (270 to 4500 kg/hr) depending on the size distribution of the incoming pecans. One may expect somewhat lower capacities if the pecans consist of a high percentage of a single size nut. For pecans, the openings in the sizer are normally graduated in sixteenths of an inch 0.6 mm). After cleaning, grading and sizing, the pecans are ready to be cracked and shelled. These operations will be discussed in the following section. Conveying Equipment Product transportation systems (i.e., conveyors) play an important role in any modem processing facility. Proper sizing of a conveyor system, its placement and maintenance will save on transportation time and labor while increasing production capacity and efficiency. Equipment used to transport a product(s) throughout the processing facility can be broadly classified as belt conveyors, chain conveyors, gravity (roller) conveyors or vibrating conveyors. In pecan shelling plants, belt and vibrating conveyors are generally employed to move the products (e.g., whole pecans, cracked pecans, shell pieces and nut meats) from one operation to another. Because of their importance in pecan shelling, these conveying systems will be discussed in more detail. Although elevating equipment and let-down chutes will not be discussed here, their role in product transport should not be overlooked. In simple terms, conveyors are nothing more than a table (commonly referred to as the trough) with a moving or vibrating surface which mayor may not be flat depending on the product. The conveyor's main function is to move the product from one point to another in an efficient and gentle manner. Regardless of the mechanism used to "move" the product, all conveyors have some common

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design and construction features. For example, when the conveying system is to be used in a food processing facility, two very important design criteria are sanitary construction and ease of cleaning. In the past, manufacturers of foodgrade conveyors were generally limited to the use of stainless steel in the construction of troughs. However, technological advances in the manufacture of engineering plastics and resins has led to alternative materials of construction for use in some conveying systems while simultaneously reducing the overall weight of the trough. Troughs are available in widths ranging from 6--48 in. (15-22 cm). This gives the processor the opportunity to select a trough width that best suits their production requirements. For vibrating conveyors, trough depth must also be specified and generally ranges from six to eight inches (15 to 20 cm). Food-grade troughs are designed to minimize the risk of product contamination. Stainless steel troughs are welded, thus no bolts or rivets are required. This decreases the possibility of trapping dirt and micro-organisms and aids in cleanup. Dust and/or weather-tight covers can also be placed on troughs to further reduce the risk of product contamination. The differences between belt and vibrating conveyors is briefly discussed below. Belt Conveyors As the name implies, these conveyors utilize a rotating belt or belting material for product transport. Some standard features on belt conveyors include belt tension adjustment (i.e., takeup), a drive system to provide movement of the belt and a slider bed on which the moving belt sits. Some optional features available on belt conveyors include vacuum breaks in slider beds to eliminate belt sticking after washdown or when handling wet products, custom designed inlets and discharge chutes, flat or hip roof-type dust/weather covers. Vibrating Conveyors Unlike belt conveyors in which the trough or belt moves with the product, in vibrating conveyors the trough is essentially stationary. Product movement is accomplished through the back and forth shaking motion of the trough. Because of this type of motion, the design of a vibrating conveyor is somewhat more complicated than a belt conveyor. Smooth gentle operation of vibrating conveyors will be based on several factors including the type of drive, counterweight, spring and isolation (shock absorbing) systems used. Vibrating conveyors can be subdivided according to the mechanism used to generate the vibrational force on the trough. Three common mechanisms include inertially driven systems, eccentrically driven systems and natural frequency-counterbalanced systems. The Meyer Machine Company has put together a very helpful set of brochures and bulletins, complete with drawings and photos, describing the company's belt

Mechanization of Post-Harvest Pecan Processing / 71

and vibrating conveyors. Additional information regarding specific applications and designs should be obtained directly from the various manufacturers of the conveying system(s). Pecan Cracking and Shelling

Conditioning of the Pecan Nut Prior to cracking and shelling, the pecan nut is water conditioned or tempered in order to prevent extensive damage to the meat. Conditioning results in an increased moisture content of the pecan meats due to the migration of water into the shell. For the most satisfactory cracking and shelling, the shells should be dry, brittle and easily shattered, while the kernels should be limp and pliable (Heaton et al. 1977). Several pecan conditioning techniques are available. A brief summary of the most common conditioning techniques, as discussed by Woodroof (1979), follows. The most common conditioning techniques include: 1) the cold water method; 2) the pressurized steam method; and 3) the hot water method. In the cold water method, pecans are soaked for 20 to 30 min in water containing 1000 ppm chlorine, drained and then held for cracking at any time within the next 24 hours. For the pressurized steam method, pecans are subjected to low pressure steam (approximately 5 psig) for six to eight minutes. The pecans are then cooled and held for 30 to 60 minutes. This method is fast, but less effective in controlling mold than the cold water method due to the simultaneous exposure to chlorine. The hot water method is not only fast but yields high quality pecan meats. In this method, the pecans are immersed for approximately 20 minutes in water that has been heated to 62.8°C (145°F). The pecans are immediately shelled after immersing for the required time period. To improve water penetration, wetting agents (e.g., sodium tetraphosphate, santomerse or polyoxyethylene sorbitan (Tween 85) may also be used with either the hot or cold water methods described above. Exposing pecans to vacuum prior to immersing them in water has also been used to improve water penetration into the pecan (Woodroof 1979). Conditioning equipment can vary from simple stainless steel tanks operated as individual batch conditioners to continuously operated conditioners with capacities of 4,000 to 7,000 Ibs/hr (1800 to 3150 kg/hr). Cracking Equipment Cracking is a critical part of the overall post-harvest pecan processing operation. The objective in the cracking operation is to initiate the separation of the shell from the meat while attempting to maintain the pecan meat in large unbroken halves. The nuts are individually cracked through the application of mechanical

72 / Kevin A. Sims

force to each end. Tests have shown that 'Stuart' pecans of average shell thickness require more than 200 lbs (90 kg) of pressure to shatter, while some cultivars require as much as 600 lbs (270 kg) of applied pressure (Woodroof 1979). Properly designed crackers should crack each nut in such a fashion that separation of the meat from the shell is easily accomplished with minimum damage to the pecan halves. To help insure a high percentage of pecan halves after cracking, grading of in-shell nuts is important so that pockets in the cracking unit can be properly adjusted prior to starting the cracking operation. Several manufacturers of cracking equipment exist. Two of the larger manufacturers are Meyer Machine Company (San Antonio, TX), builders of the first automatic cracker, and Machine Design Incorporated (Columbia, SC). The cracker manufactured by Machine Design Inc. is more commonly known as the Quantz cracker named after James B. Quantz, the company President. The Meyer cracker consists of interchangeable nut pockets, which allows one cracker to crack nuts of various sizes. According to Meyer company literature (Bulletin 914-B), approximately 86 nuts per minute can be cracked with minimum adjustments to the cracker. The number of crackers required for a particular pecan processing operation will depend on the amount of pecans the shelling plant handles in a normal working day. Shelling plants that crack large volumes of pecans meet production quotas by arranging individual crackers in a series of rows or banks. Each cracker in the bank thus provides a portion of the total amount of cracked pecans that will undergo further processing. After cracking, the nuts are conveyed by belts to the shelling units where the meats and shells are separated. Shelling Equipment

Shelling can be considered to include all the various operations used to complete the separation of the pecan shells from the meats following cracking. Equipment used in these operations include shellers, vibrating tables with screens, inspection tables, and electronic sorters used to separate shell fragments and pieces from the meats. The electronic sorting equipment is also used to separate the various meat pieces based on uniformity of color. Shelling machines are available in several sizes to accommodate both the large and small pecan processing operations. One sheller is able to efficiently handle the output from several crackers, thus the number of shellers required to process a given amount of pecans is significantly less than the number of crackers. In addition to the throughput of the machinery, shellers are available with various features which are based on the size of the overall shelling operation. Some of the features include variable adjustments of the spacing between the shelling rings and an optional fan for removing shell debris, dust and insects. Meyer Machine Company (San Antonio, TX) manufactures three shellers that differ in shelling capacity and features. One of the smaller units, the Meyer

Mechanization of Post-Harvest Pecan Processing / 73

Junior Sheller, handles the output of up to five crackers or up to 450 lbs (203 kg) of pecans/hr. Spacing on this unit is adjusted manually by changing the spacers between the shelling rings. Three sets of spacers at 3/8 in. (9.4 mm), 5/16 in. (7.8 mm) and 114 in. (6.2 mm) are provided with each sheller. A suction fan is not provided with this unit. One of the company's larger units, the 18 in. (46 cm) diameter dial-type adustable sheller, enables you to adjust the sheller ring opening to a desired size by simply turning a handle. The unit is capable of shelling the output of 12 to 15 crackers (1,100 to 1,350 lbs (495 to 608 kg) of pecans/hr) and is available with and without a suction fan. Separation of Nut Meats From Shell Pieces

After the cracking and preliminary shelling operations are completed, there is still a considerable amount of pecan meat that must be separated from either shell pieces or fragments. To produce a quality product with a minimum amount of shell residue, additional processing steps are required. These additional processing steps often utilize a simple water flotation technique that takes advantage of the density difference that exists between the nut meat and the shell to perform the separation. One disadvantage of water flotation is the additional drying required to remove water from the pecan meats. Traditional flotation systems employ vacuum to remove air trapped in shell pockets. Once the air has escaped, the shell pieces sink to the bottom of the flotation tank, while the meats remain on the surface. The vacuum flotation equipment commonly used is available for both batch and continuous pecan shelling operations. The equipment is designed with few moving parts to provide easy maintenance and trouble-free operation. Meyer Machine Company's continuous vacuum floating separator will separate greater than 99% of the nut meats from the shell pieces if stick-tights, partitions and light weight, pithy meats have been previously removed.

Insect Removal A variety of insects infect pecans and their potential to damage a pecan crop can be tremendous. Some of the more prominent insect pests found in pecan orchards include the pecan or hickory shuckworm (Laspeyresia caryana Fitch), the pecan nut casebearer (Acrobasis carya Grote), the southern green stink bug (Nezara viridula L) and the pecan weevil (Curculio caryae Hom.). The pecan weevil, which completes its metamorphasis as a larvae inside of the pecan shell, is probably considered the most destructive pecan insect. Although it is not present in all the pecan orchards in Georgia, the pecan weevil has become widespread during the last few years where it damages nuts in nearly all Georgia counties where pecans are produced (Ellis 1985). Removal of insects during the various shelling operations is essential to mini-

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mize problems that may arise during storage of the pecan meats. Although insects may be partially removed throughout the entire shelling process by size separation, a final visual inspection is often required to remove any insects or insect fragments that remain with the nut meats. Toledo (1978) developed and patented a flotation process utilizing alcohol as the continuous phase (i.e., the suspending fluid). The use of alcohol was required because both the pecan meats and insects have a specific gravity less than water, thus they would both float if water were used as the continuous phase and no separation would occur. Although the alcohol flotation process can replace the traditional labor intensive visual inspection, it has not been widely adopted in the industry. Inspection and Grading of Pecan Meats

Given that pecan meats can be completely separated from foreign material, they must be graded and inspected to determine the appropriate market. Most pecan shelling plants still rely on manual inspection, whether it is to remove insects or small shell fragments that were not completely removed at an earlier point in the operation. Manual inspection is typically conducted on a belt-type conveyor. Depending on the product, colored belts can be used to increase product visibility and reduce eye fatigue. An important part of the inspection process is the steady uninterrupted flow of product past the inspectors. Vibrating hoppers/feeders, available in several sizes and materials, are most often used to accomplish this. Product feed rates can be adjusted to meet specific processing/production requirements. Vibrating tables, equipped with two or more working surfaces at slightly different heights, are used to automatically flip the product as it passes from one belt to the other. This allows the operator to view the product from at least two different sides. Vibrating tables can also be used to separate pecan meats from shell pieces and weevil larvae based on differences in elasticity and density. In addition to separating pecan meats from insects, insect fragments and/or small shell pieces, the meats can also be separated on the basis of color. Electronic color sorters are used to grade pecan meats on the basis of color. Today's color sorters are not only faster than manual inspection, they are capable of viewing the pecan meat continuously from multiple directions and can be used around the clock. This ensures that even the smallest defects (i.e., color blemishes) are picked up. Sortex-Scancore is one manufacturer of electronic color sorters. The company's Ultra-Sort unit utilizes monochromatic light to sort various types of beans, nuts, seeds and other products. The Ultra-Sort is available with either 1, 2 or 4 channels and can also be supplied with white, infra-red or ultra-violet light for maximum flexibility. The 4-channel model can also be equipped with a microprocessor control unit, which in conjunction with a color video display enables the user to easily set up and adjust operating parameters and continuously

Mechanization of Post-Harvest Pecan Processing / 75

monitor the equipment's performance. The capacity of these color sorters is highly dependent on the commodity being sorted, its size and shape and the quality requirements established by the customer. All of the Ultra-Sort units require a nominal air pressure of 60 psig. Air consumption rates are dependent on the number of channels and the rejection rate of the product. Drying Equipment

Proper drying of pecans and pecan meats is critical to maintain product quality during storage. Nuts and meats containing an excessive amount of moisture are susceptible to several mechanisms of deterioration including mold growth, discoloration and oil breakdown (Woodroof and Heaton 1961). Under poor storage conditions (i.e., high temperatures and excessive relative humidities), the market value of both pecans and pecan meats decreases rapidly. Pecans need to be dried to a moisture level of approximately 4.5% as soon as possible after harvesting to prevent molding, discoloration and oil breakdown (Woodroof and Heaton 1961). Pecan meats contain 7-9 percent moisture when shelled and should be reduced to 3-5 percent or lower to maintain meat quality and minimize problems during storage (Woodroof and Heaton 1961). Chapter 4 of this book contains specific information regarding drying conditions in order to maintain the quality of pecans and pecan meats. In-shell Drying

Several options are available for drying in-shell pecans. These include drying without additional heat, drying with added heat and drying under refrigeration. Table 5.1 shows the effects of drying temperature, relative humidity and air velocity on the time required to dry in-shell pecans from 8.0% to 4.4% moisture. Drying was accelerated by increasing temperature and air velocity and decreasing the relative humidity (Heaton et al. 1977). Pecan farmers can purchase their own drying equipment and perform the drying operation themselves. The farmer also needs to consider if drying will be accomplished with additional heat or if ambient air temperatures are sufficient to reduce the moisture content of the pecans. After harvesting and prior to drying, the pecans are cleaned sufficiently to remove any large sticks, leaves and rocks. This increases drying efficiency and decreases drying time. The pecans are then generally placed in burlap sacks (80 to 100 lbs (36 to 45 kg) of pecans per sack) in preparation for drying, storage and transportation. If the farmer chooses to dry the pecans himself, the bags could be loaded into drying trailers equipped with fan hook-ups. These portable trailers are used to aid the farmer in harvesting, drying and transporting the pecans to the shelling plant or wholesale dealer. Peerless Manufacturing Company (Shellman, GA) is one supplier of portable drying trailers. The trailers are

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Table 5 .1. Effect of drying conditions on reduction of kernel moisture from 8.0 to 4.4% in in-shell pecans . Temperature

Relative Humidity




32 SO 66 66 70 78 102

0 10 19 19 21 2S 39

60 60

40 40 SO 39 9

Air Movement CFM (m'/min)

Drying Time

slight slight 0 640 (18.1) slight 300 (8.S) 420 (11.9)

4-6 weeks 3-4 weeks 2-3 weeks IS hr 2-3 weeks 17 hr 9 hr

Adapted from Heaton et al. (1977).

available in two sizes (14 ft (4.3 m) and 21 ft (6.4 m)) and a variety of options including number of axles, hydraulic dumping capabilities, location of the air vents and the type of mechanism used to attach the trailer to the towing vehicle. Figures 5.1 through 5.3 illustrate two types of drying trailers. In addition to manufacturing trailers, the company also supplies the dryers and/or aeration fans used for in-shell drying. The dryers are equipped with self cleaning gas burners capable of delivering 1.1 million BTU's of heat. No heating

Figure 5 .1. Trailers (14 ft (4.3 m» side opening drying wagon) used for harvesting, drying and transporting of pecans from the orchard to the shelling plant. (photos courtesy of Peerless Manufacturing Co.)

Figure 5.2. Trailers (14 ft (4.3 m) single axle with tandem wheels and rear opening drying wagon) used for harvesting, drying and transporting of pecans from the orchard to the shelling plant. (photos courtesy of Peerless Manufacturing Co.)

Figure 5.3. Trailers (14 ft (4.3 m) with Jet Dryer) used for harvesting, drying and transporting of pecans from the orchard to the shelling plant. (photos courtesy of Peerless Manufacturing Co.)


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Figure 5.4. Peerless Jet Dryer-Vane Axial Type. Dryer can be mounted on a swing arm to eliminate moving a trailer into position. Two sizes of motors are available (5-7 HP or 10-12 HP) providing a wide range of volumetric air flow rates. (photos courtesyy of Peerless Manufacturing Co.)

source is provided with the aeration fans. The dryers are easily attached to the company's drying trailers via the air vent. Four types of dryers are available; the Jet Dryer, the Whisper Jet Dryer, a Dual Dryer and a Whisper Dual Dryer. The difference between the regular dryers and the "Whisper" dryers is the type of fan used to circulate the heated air. The "Whisper" dryers are constructed using backward incline (curved) fans (Figures 5.4 through 5.7). The "Dual" dryers are equipped with two air vent attachments, allowing the dryer to simultaneously dry two trailers containing pecans. In addition to the type of fan used in the dryer, one must also consider the size of the motor required for their specific drying needs. The size of the motor, along with the static back-pressure created by the moist pecans, will influence the volumetric flow rate of the heated air (i.e. , ft3 per min). According to company literature, the 22 in. (56 cm) Jet Dryer, equipped with 5-7 horsepower (HP) motor, will deliver approximately 8,500 fe per min (CFM) at a static pressure of 3 in. (7.6 cm) water and 11 ,300 CFM (320 m3/min) at a static pressure 0.5 in. (1.27 cm) water. With a 26 in. (66 cm) fan and a 10-12 HP motor, the dryer will deliver 14,800 CFM (419 m3/min) at a static pressure of 3 in. (7.6 cm) water and 17,400 CFM (493 m3/min) at a static pressure of 0.5 in. (1.27 cm) water.

Figure 5.5.

Peerless Jet Dryer-Vane Axial Type. Cut away view. (photos courtesy of Peerless Manufacturing Co.)

Figure 5.6.

Peerless Whisper Jet Dryer equipped with a backward incline (curved) fan for quieter operation. The dryer is mounted on skids for easy moving and available with a 5 HP motor. (photos courtesy of Peerless Manufacturing Co.)


80 / Kevin A. Sims

Figure 5.7. Peerless Jet Dryer-Vane Axial Type Dual Dryer 10-12 HP. (photos courtesy of Peerless Manufacturing Co.)

Pecan farmers can opt to dry the harvested pecans without using any additional heat. In this case, an aeration or circulation fan should be used to provide sufficient air flow to decrease the moisture content of the pecans and increase storage life. Peerless makes aeration fans in three sizes; 18,22 and 26 in. (46, 56 and 66 cm). As with the dryers, performance of the aeration fans will be based on both the size ofthe motor and the static back-pressure. Air flow rates from 5 ,000 CFM to 17,400 CFM (142 to 493 m 3/min) can be achieved, thus providing the operator with the flexibility often required when drying pecans or any other type of harvested crop that is susceptible to changing environmental conditions. Drying of Nut Meats

As mentioned above, the moisture content of pecan meats should also be reduced as soon as possible to prolong storage and maintain product quality. Woodroof and Heaton (1961) stated that the final moisture content of pecan meats should be around 4% after drying, however, a more recent study by Heaton et al. (1977) reported that the moisture content of pecan meats should be reduced to about 3.5%. Table 5.2 shows the effects of drying temperature and time on the final moisture content of 'Stuart' pecan halves. The quality of the pecan halves before drying and after six months storage at O°C (32°F) is also shown.

Mechanization of Post-Harvest Pecan Processing / 81 Table 5.2. Effect of drying conditions on the moisture level and quality of 'Stuart' pecan halves. Drying Temp.

Quality score (100 = Max)



Drying Time




After Drying

After Storage (6 months)

0 20 70 80 100 120 140 160 180 200

-22 -7 21 27 38 49 60 71 82 94

168 168 48 15 2.75 1.75 1.25 1.00 0.75 0.50

3.83 3.78 4.06 3.56 4.16 3.59 3.44 3.14 2.65 2.76

88.9 88.9 88.9 88.9 86.7 85.6 83.3 84.4 83.3 84.4

88.9 88.9 88.9 88.9 85.6 86.7 82.2 81.1 76.7 71.1

Adapted from Heaton et aJ. (1977).

Table 5.3 shows the results of an experiment used to determine the equilibrium moisture content of 'Stuart' pecan halves at various storage temperatures and relative humidities. The data indicates that pecan halves could be dried to a safe moisture level (~ 4%) during storage at several temperatures and relative humidities. Dryers have been specifically designed for the rapid and efficient drying of both pecans halves and pieces. These dryers can be operated either in a batch process or continually. In addition to drying the nut meats, some manufacturers provide cooling units as an integral part of their dryer designs. Examples include the Vertical Continuous Dryer-Cooler and the Batch Dryer-Cooler which are manufactured by Meyer Machine Company. The National Drying Machinery Company also manufactures dryers which are used in the dehydration of different tree nuts. The Vertical Continuous Dryer-Cooler is designed to dry and cool nut meats in a single operation. The vertical design permits effective utilization of the available floor space. The dryers are available in several sizes and proper selection is based on both the type and quantity of nut meats to be dried. Multiple drying and cooling stages within a single unit provide the sheller with greater flexibility and the sectional construction of the dryers allows for plant capacity increases at later dates. For drying pecan "halves" the most common dryer is the two-stage halves dryer-cooler. The unit consists of one drying stage and one cooling stage with an approximate capacity of 1,000 lbs (2200 kg) of nut meat halves per hour at normal moistures. The temperature can be adjusted to over 94°C (200°F) and the heater output ranges from 0 to 500,000 BTUs. Drying of pecan "pieces" requires removal of the excess moisture that the nut

82 I Kevin A. Sims Table 5.3. The influence of temperature and relative humidity on equilibrium moisture content of 'Stuart' pecan halves. Temperature ("C)


Relative Humidity (%)

Initial Moisture Content (%)

Equilibrium Moisture Content (%)

-6.7° -17.8° -17.8° -17.8° -17.8° -9.4° -6.7° -6.7° -6.7° -6.7° -3.9° -3.9° -3.9° -3.9° 0° 0° 0° 0° 0° 0° 10° 21.1°

20° 0° 0° 0° 0° 15° 20° 20° 20° 20° 25° 25° 25° 25° 32° 32° 32° 32° 32° 32° 50° 70°

45-50 55-60 65-70 65-70 65-70 55-60 60-65 75-80 75-80 75-80 70-75 70-75 70-75 70-75 35-40 65-70 75-80 75-80 75-80 75-80 50-65 50-65

2.58 2.58 1.67 2.18 6.37 7.45 2.58 1.67 2.18 6.37 1.67 2.18 2.58 6.37 3.41 3.41 1.67 2.18 2.58 6.37 7.20 7.20

3.78 3.61 4.46 4.57 4.76 3.71 3.50 6.34 6.77 6.18 3.90 3.87 3.90 3.92 2.34 4.94 4.75 4.91 4.51 5.07 3.00 2.80

Adapted from Woodroof (1979).

meat has picked up as a result of prior processing steps (e.g., flotation and extraction). To remove this added moisture, additional drying and cooling stages have been added to the Meyer Vertical Continuous Dryer-Coolers. Some of the more popular models include the three-, four-, and five-stage dryer-coolers. The three- and four-stage models are contained in a single unit, while the five-stage model consists of two separate units for drying and cooling. Meyer provides product transfer via a conveying elevator as an integral part of the five-stage unit. The three- and four-stage models contain a single cooling stage (the remaining stages are used for drying) and the five-stage model, the company's largest standard production unit, consists of three drying stages and two cooling stages. The three-stage unit has an approximate capacity of 500 lbs (225 kg) of floated and extracted nut meat pieces per hour. The capacity of the four-stage unit is approximately 800 lbs (360 kg) per hour, while the five-stage unit will dry and cool nearly 1,000 lbs (450 kg) per hour. The drying capacity will depend on the type and size of the product, the initial moisture content and the desired final moisture content. As with the two-stage "halves" dryer-cooler, the temperature is adjustable to over 94°C (200°F) and the BTU range is from 0 to 500,000.

Mechanization of Post-Harvest Pecan Processing / 83

Storage, Refrigeration and Packaging of Pecans

The supply of pecans has exceeded consumption every year since the 197677 growing season (Dell 1990). Data indicates that the supply has exceeded consumption by a minimum of 20 million pounds (9,090 metric tons) (1976-77 growing season) to as much as 119 million pounds (54,090 metric tons) during the 1981-82 growing season. Because of this excess supply, there is a significant amount of pecans placed in storage every year. To maintain high quality pecans during storage, proper packaging and refrigeration procedures must be followed. Storage and packaging practices for pecans will be discussed briefly in this section. Storage and Refrigeration of Pecans

Proper storage will help maintain the keeping quality and marketability of pecans for extended periods, while preventing or retarding the development of many physical, chemical and biological processes that lead to decreased quality. Experiments conducted at the University of Georgia Experiment Station have shown that controlled refrigerated storage prevents molding, delays onset of staling and rancidity, inhibits insects and preserves the color, flavor and texture of shelled pecans for as long as eight years (Woodroof 1979). Freezing has also been found to be an excellent storage procedure for both unshelled and shelled pecans. No significant damage, increase in oil seepage or decrease in quality was observed in pecans stored at temperatures as low as - 128°C ( -170°F) (Heaton et al. 1977). However, frozen pecans are quite brittle and breakage may occur if they are not handled properly. Upon removal from a freezer, frozen pecans should be allowed to thaw or "temper" for a few hours before shipping (Woodroof 1979). Tempering also helps to prevent surface condensation and mold growth on the pecans. Pecans may also be stored for shorter periods at room temperature without significant loss of quality if precautions are taken in terms of proper packaging. Santerre et al. (1990) have studied the effects of room temperature storage on shelled pecans under atmospheric and modified atmosphere conditions using several different types of packaging materials. Sensory flavor, internal flesh color and texture changes were detected in pecans which were stored in low oxygen environments or with oxygen barrier coatings. The changes included flesh darkening, softening texture and the development of a "fruity flavor." Table 5.4 shows that pecan varieties with a higher fat content tend to be more stable during storage than pecans with lower fat contents. Packaging of Pecans

In-shell pecans are naturally protected from environmental and biological attack provided that the shells are intact. On the other hand, pecan meats must be

84 / Kevin A. Sims Table 5.4.

Quality of six varieties of pecan halves stored at O°C (32 0 Ft. Halves

Moisture Content

Fat Content
























2.2 10 13 3.5 10 13 2.5 10 13 3.2 10 13 3.2 10 13 3.9 10 13

75.9 80.0 63.8 73.1 78.9 67.4 72.6 77.8 73.3 73.4 77.8 70.4 73.1 61.1 56.3 68.7 55.6 49.4

Storage Time (mon)

Quality Score (100 = max)













Adapted from Heaton et a1. (1977) . • Listed in order of the initial quality of the pecans.

properly packaged in order to maintain their quality throughout the storage period. The amount of humidity and the type of light and air that pecans are exposed to during storage are important environmental conditions that must be considered. Insects, rodents and molds are sources of potential biological problems that decrease pecan quality and may render the product unmarketable. A large portion of shelled pecans are packaged in grease-proof cartons made of corrugated cardboard (Heaton et al. 1977). Other common packaging materials include tin cans, glass jars, aluminum foil pouches and flexible bags made from Saran®, Mylar®, nylon, polyethylene or cellophane. Table 5.5 lists common packaging materials, including some of their properties, used for storing pecans. Studies have shown that vacuum packaging or carbon dioxide flushing significantly extends the storage life of both raw and roasted pecans (Heaton 1977). Dull and Kays (1988) found that 'Stuart' pecan kernels packaged in polyvinylidene chloride (PVDC) coated cellophane films with low oxygen transmission rates were of acceptable quality after six months storage at 24°C (75°F) and 60% relative humidity.

Heating and Roasting of Pecan Meats Heating pecan meats to an internal temperature of 80°C (176°F), in either dry air or oil, has been shown to increase shelf life through inactivation of oxidative

Mechanization of Post-Harvest Pecan Processing / 85 Table 5.5.

Packaging containers for storing pecans. a

Container Type

Oxygen Penneability

Moisture Penneability (g/24 hr/100 in. 2) (g/24 hrs/645 cm2)

Tin cans Glass jars Saran® bags Aluminum foil pouches Greaseproof boxes Antioxidant treated boxes MylarCl!> bags Nylon bags Cellophane bags Polyethylene bags Glassine lined bags Plain boxes Kraft bags

NAb NA very low NA

0 0 0.1-0.3 0

NA NA moderate NA











very low very low very low

1.8 1.5 0.2-1.0

slight slight moderate


4 4 3











very high very high

high high

high high

5 5

Storage Life (months)

Suceptibility to insect attack

O°C (32OP) 30+ 30+ 30 30+


21°C (70°F) 5 4 4

2 0.75

Adapted from Heaton et al. (1977). "Listed in order of preference ~ot Applicable.

enzymes (Woodroof and Heaton 1961; McGlammery and Hood 1951). However, heating to higher temperatures produces a partially cooked flavor and may destroy the natural antioxidants present in pecans, thus increasing the likelihood of developing oxidative rancidity during storage (Woodroof 1979). Dry or oil roasting of pecan meats, when properly conducted, leads to an increased flavor and aroma in the finished product. A complete line of dry roasting equipment is available from the National Drying Machinery Company. Their roasters offer a full range of applications including; blanch roasting, dry roasting and in-shell roasting. Modular construction design allows the company to provide any continuous length required for a roasting operation. The roasters have standard conveyor widths (4,6, 8, 10 and 12 ft; 1.2, 1.8, 2.4, 3.05 and 3.7 m) or custom widths may also be specified. Conclusions The purpose of this chapter is to give the reader an overview of the major processing operations used in the pecan shelling industry. When possible, specific

86 / Kevin A. Sims

types of equipment currently being used are discussed. However, as with all processing industries, new equipment is constantly being designed and evaluated. Hence, while the information presented in this chapter is correct, it should be considered as a general reference. Specific capacities of dryers or crackers, for example, along with specific size measurements are subject to change as equipment manufacturers develop new innovations and materials of construction.

Acknowledgments The author would like to thank all the people that contributed to this chapter on the type of processing equipment used in the pecan shelling industry. Much of the information presented here was obtained from personal communications or derived from company literature. I am especially thankful to Mr. Seaborn Dell, Production Manager, for giving me the opportunity to visit the Tracy-Luckey plant located in Harlem, GA. I am also thankful to Mr. Eugene W. Teeter, President, Meyer Machine Company and Mr. Marvin Waddell, Vice President of Sales, Peerless Manufacturing Company for supplying me with a tremendous amount of material on nut processing equipment in general.

References Dell, S. 1990. Personal communication Dull, G.G. and S.J. Kays. 1988. Quality and mechanical stability of pecan kernels with different packaging protocols. J. Food Sci. 53:565. Ellis, H.C. 1985. Pecan weevil. Cooperative Extension Service, University of Georgia! College of Agriculture. Leaflet #26. Heaton, E.K., A.L. Shewfelt, A.E. Badenhop, andL.R. Beuchat. 1977. Pecans: handling, storage, processing & utilization. University of Georgia!College of Agriculture. Georgia Experiment Station Research Bulletin 197. McGlammery, J.B. and M.P. Hood, 1951. Effect of two heat treatments on rancidity in unshelled pecans. Food Technol. 16:80--84. Meyer Machine Company. Meyer Automatic Edible Nut Crackers. Bulletin 914-B. Santerre, C.R., A.J. Scouten, and M.S. Chinnan, 1990. Room temperature storage of shelled pecans: control of oxygen. Proceedings of the Southeastern Pecan Growers Association. 83rd Annual Convention. Destin, FL: 113-121. Toledo, R.T. 1978. U.S. Patent # 4,082,655. Woodroof, J.G. and E.K. Heaton. 1961. Pecans for processing. University of Georgia! College of Agriculture. Bulletin N.S. 80. Woodroof, J.G. 1979. Pecans. In Tree Nuts: Production, Processing, Products, 2nd ed. CT: A VI Publishing Co.

6 Microbiology and Sanitation Larry R. Beuchat

Introduction The incidence of major groups of microorganisms (molds and bacteria) which contaminate and can cause spoilage of pecans is widespread. Many types of microorganisms can be found in pecan groves, processing plants, and commercial distribution centers. The problem is one of microbiological control and not, with few exceptions, elimination from pecans. Exposure of nuts to various contaminating influences such as weather conditions, particularly air movement and rainfall, dust from soil, animals such as cattle, horses, goats, squirrels and birds, and sub-optimal storage conditions all contribute to the microbial quality of pecans. Molds on Pecans Pecans are subjected to mold contamination at various stages of development and processing. There are several dozen genera of molds which may invade the nut from the early stages of development on the tree to the time it is processed and ready for consumption. Listed in Table 6.1 are some of the genera of molds which have been isolated from pecans. An exhaustive study to determine the mycoflora present on pecans grown in various locations and subjected to various storage, processing, packaging and distribution systems has not been reported. It is very likely that several additional mold genera and species would be detected on pecans subjected to diverse growing and handling conditions. Hanlin and his colleagues at the University of Georgia have done the most extensive work on mycology of pecans. Molds are present on pecan kernels, shells and husks throughout the growing season. Hanlin (1971) quantitated and identified molds on pecans from shortly after fertilization through maturity. He C. R. Santerre (ed.), Pecan Technology © Chapman & Hall, Inc. 1994


88 / Larry R. Beuchat Table 6.1.

Genera of molds isolated from pecans·

Absidia Alternata Arthrinium Ascochyta Aspergillus Aureobasidium Botryodiplodia Cephalosporium Chaetomium Cladosporium Coniothyrium Curvularia Diaporthe Didymella Diplodia

Emericella Epicoccum Eurotium Fusarium Geniculisporium Humicola Itersonilia Libertella Microascus Mucor Nigrospora Nodulisporium Penicillium Periconia

Pestalotia Petriella Phoma Pleospora Rhinocladiella Rhizopus Scopulariopsis Sordaria Syncephalastrum Talaromyces Torula Trichothecium Wallemia Xylaria

aAdapted from: Hanlin (1971, 1972); Huang and Hanlin (1975); Lillard, Hanlin and Lillard (1970); Wells and Payne (1976); Chipley and Heaton (1971); Schindler et al. (1974).

found that young pecan fruits are invaded by a variety of fungi as soon as they begin to develop on the tree. Molds present in the kernel were very similar to those in the shell, thus suggesting that seed invasion takes place while the kernel is still in the shell. Nearly 100% of the seeds contained mold at maturity. The three most common genera in husks were Phoma, Alternaria and Pestalotia. Pestalotia, Fusarium and Cladosporium species are most prevalent on shells whereas Cladosporium, Fusarium and Penicillium species are most common on kernels. Hanlin and Blanchard (1974) continued to study the molds associated with developing pecans. They reported that nine genera (Alternaria, Aspergillus, Cladosporium, Curvularia, Fusarium, Nigrospora, Penicillium, Pestalotia and Phoma) were present in all parts of the pecan fruit and accounted for the majority of isolates. In a later study, Huang and Hanlin (1975) conducted a survey to determine the molds associated with freshly harvested and market pecans. Forty-four genera and 119 species were identified. Thirty genera occurred only in freshly harvested pecans, 16 genera occurred only in freshly harvested and market samples and six genera occurred only in market pecans. On freshly harvested pecans, Penicillium species were most common, followed by species of Aspergillus, Pestalotia, Rhizopus and Fusarium. These molds and others which may be commonly present on freshly harvested pecans are undoubtedly representative of the normal mycoflora. After storage, market samples of pecans contained Aspergillus as the dominant genus, Penicillium being second in predominance. Eurotium species increased tremendously in market pecans, while Pestalotia and Fusarium isolates decreased. On the basis of the number of isolates, Huang and Hanlin (1975)

Microbiology and Sanitation / 89

divided Penicillium and Aspergillus (perfect state-Eurotium) species into four categories: 1.

Field Penicillium-Po cyclopium, P. decumbens series, P. steckii and P. urticae


Storage Penicillium-Po citrinum, P. expansum, P. lanosum and P. roquefortii


Storage Aspergillus-A. fiavus, A. niger and A. parasiticus


Storage Eurotium-E. repens and E. rubrum

The presence of A. fiavus and A. parasiticus in stored pecans is of public health significance. Due to the lack of appropriate taxonomic guides to identify Sordaria species on pecans in field laboratories, Hanlin (1972) published a report to aid in their identification. Increased interest in the microbial quality of pecans indicates the need for additional identification schemes written specifically for use in processing quality control laboratories.

Mycotoxins The vast majority of molds are harmless from the standpoint of public health; however, they may cause substantial loss in product due to sensory quality deterioration as a result of growth. Some strains of A. fiavus and A. parasiticus can produce a series of secondary metabolites or byproducts known as aflatoxins, which are carcinogenic and toxic to various animal species. It is the presence of aflatoxins as well as other mold toxins (mycotoxins) which might be produced in moldy pecans that are of interest to federal and state public health agencies as well as to the consumer. Lillard, Hanlin and Lillard (1970) isolated aflatoxigenic strains of A. fiavus from pecans destined for use in bakery products and reported that pecans were a good substrate to support the growth of A. fiavus. Later Escher, Koehler and Ayres (1974) studied the occurrence of A. fiavus and toxin distribution in lots of pecans that enter the shelling plant. They reported that despite the fact that airclassification of in-shell pecans permits a partial rejection of nuts with shriveled, discolored or visibly molded meats, no significant separation of nuts containing aflatoxins or spores of A. fiavus or A. parasiticus was possible. In other words, the sheller cannot be assured that potentially toxigenic nuts are segregated from sound nuts in the blow-out fraction. Several investigators have studied the molds of pecans with particular emphasis on determining the prevalence of mycotoxin producers. Wells and Payne (1976) examined mycoflora in weevil-damaged pecans. Three of 23 Aspergillus isolates, 34 of 105 Penicillium isolates and three of 28 Fusarium isolates were toxic to day-old cockerels. Eight of the toxic extracts from Penicillium species were

90 / Larry R. Beuchat

tremorgenic. These toxigenic molds were not surface contaminants but well established in discolored pecan tissues adjoining insect-damaged areas. The potential of mycotoxin production in these pecans emphasizes the need for programs designed to eradicate insect infestation in orchards and maintain rigorous quality assurance schemes during postharvest handling, processing and distribution. The suitability of pecan kernels to support growth and aflatoxin production may be correlated with yield capacity of trees on which they are produced. McMeans (1983) inoculated kernel meats from high-, medium- and low-yielding trees with A. parasiticus. After incubation at 25°C (76°F) for seven days, significant differences in aflatoxin accumulation were detected among the three substrates, a direct correlation existing between high aflatoxin concentration and tree yield. The intact shell of pecans provides some protection against invasion of molds, including mycotoxigenic species. However, kernels with apparently intact shells can be infected with molds. Shroeder and Storey (1976) reported the presence of aflatoxin and another mycotoxin, zearalenone, in kernels from sound nuts. Schindler et al. (1974) investigated the mycoflora of in-shell pecans. Nine genera and at least 24 species of molds were among 163 isolates, with Alternaria species (19 isolates), Aspergillus species (42 isolates, including 9 species) and Penicillium species (78 isolates, including 15 species) predominating. Isolates were demonstrated to be capable of producing several mycotoxins, including aflatoxin, sterigmatocystin and ochratoxin. Two metabolites of Alternaria species, alternariol monomethyl ether and alternariol, were extracted from discolored pecans (pickouts) from commercial shellers (Schroeder and Cole 1977). Both compounds are known to be toxic to various animal species. Koehler, Hanlin and Beraha (1975) obtained 148 isolates of A. flavus and A. parasiticus from 5,608 pecans obtained from U.S. commercial markets. The percentage of internal contamination ranged from 1.7 to 7.3 %, depending upon market location. Overall, 57% of the isolates were capable of producing aflatoxins. Over 93% of the A. parasiticus isolates produced aflatoxins, confirming the general observations that this species is more likely to be aflatoxigenic. Aflatoxins are extremely resistant to heat and remain active at normal baking temperatures. Resistance to inactivation has been demonstrated in oil at 191°C (376°F) used to roast aflatoxin-containing pecans (Escher, Koehler and Ayres 1973). Therefore, although contaminated pecans may be heat-treated to kill aflatoxigenic aspergilli, aflatoxins present prior to the treatment remain active. Bacteria on Pecans

Bacterial cells and spores are present nearly everywhere in nature and are found on pecans from the time nuts commence development and progress to maturity

Microbiology and Sanitation I 91

in the grove to the time they are consumed in the home. Although it is desirable to maintain the total number of viable bacteria on pecan nuts at a low level, particular types of bacteria such as those in the coliform group, and especially salmonellae, are more important from a public health standpoint. The presence of these bacteria, even at low levels, indicates a potential for food poisoning. One particular bacterium belonging to the coliform group is Escherichia coli, which has been used as an indicator organism because of its universal presence in the intestinal tract of most warm-blooded animals. Samples of pecans containing E. coli are therefore suspected to have been contaminated by human or other animal fecal material and thus are considered to carry additional microorganisms which might be detrimental to human health. For many years, E. coli itself was considered to be harmless. However, recent observations indicate that this bacterium can also cause human illness. Demonstrated presence and number of coliforms, in particular E. coli, on pecans is inconsistent. Ostrolenk and Welch (1941) concluded that nutrneats within the unbroken shell did not contain coliforms but that E. coli could, if introduced artificially, remain viable for 68 days. Beuchat (1973) reported that survival of E. coli on artificially inoculated pecan halves was dependent upon moisture content of pecans and storage temperature. Survival was greater on meats containing 3.47% moisture than on meats with 4.54%. E. coli generally remained alive longer when nuts were stored at 0° or 14°C (20°, 32° or 57°F) as compared to storage temperatures of 21 ° or 30°C (70° or 86°F). Some recommendations for holding the risk of E. coli and other bacterial contamination at a minimum include prohibiting domesticated animals from grazing in groves and keeping the grove as clean and free of debris as possible. Contact with droppings from livestock is one sure way to increase coliform contamination of pecans. Marcus and Amling (1973) studied the incidence of E. coli on in-shell pecans from grazed and nongrazed orchards over a two-year period. They reported that an average of 23% of pecans from grazed orchards and 4% from nongrazed orchards were positive for E. coli. Control of birds, rodents and insects from storage facilities will also serve to reduce the possibility of coliform contamination of pecans. The presence of coliforms on tree nuts is not limited to pecans. Walnuts (Meyer 1968), almonds (King, Miller and Eldridge 1970) and cashew nuts (Krishnaswamy et al. 1973) have also been documented to contain coliforms. The presence of Salmonella on pecan meats is of concern to food manufacturers of certain confectionery, drury and bakery products wherein pecans are used as ingredients without processing treatments which would be lethal to the organism. Salmonellae may remain alive and may grow in these food products, eventually causing foodborne infection if the products are eaten. Salmonellae are able to withstand 82 to 93°C (180 to 200°F) water temperature to which in-shell pecans are subjected just prior to cracking and shelling (Beuchat and Heaton 1975). The internal portions of in-shell pecans do not reach these water temperatures during


92 I Larry R. Beuchat

a two-minute treatment. These salmonellae were shown to remain viable at high levels on pecan meats for up to 32 weeks of storage at -18 and 5°C (0 and 41°F). Pecan nut packing tissue was toxic to salmonellae, thus affording some protection against high initial contamination and subsequent survival of the organisms. As in the case of E. coli survival on stored pecans, salmonellae tend to remain alive longer at refrigerated or frozen conditions. Such conditions should not be relied upon for destruction of these or other bacteria on pecans. Water Activity versus Spoilage Aside from temperature, water activity (llw) is probably the most important factor affecting the likelihood of mold growth on pecans. Water activity does not refer to the absolute water content of a foodstuff but rather the unbound, free water available to support biological and chemical reactions. Removal of water from a given foodstuff, for example pecan meats, will lower the llw. Each mold and bacterium has a minimalllw below which it will not grow. Thus, dehydration is the basic concept behind preventing mold and bacterial spoilage of pecans. Other principles such as storage temperature and atmospheric gas content are also important factors to consider when protecting pecans against microbial spoilage. Water is essential for the germination of microbial spores and for the growth of microbial cells. The availability of water for biological and chemical reactions within a microenvironment is determined by its relative vapor pressure or llw. The ratio of vapor pressure of the system (P) to the vapor pressure of pure water (Po) at the same temperature is defined as the llw of the system:

The equilibrium relative humidity (ERH) of the system, expressed in percentage, has a simple relationship to llw: ERH

= llw x


At equilibrium, P cannot be greater than Po and, thus, llw cannot be greater than 1.0 and ERH cannot be greater than 100%. The minimum llw in pecan nutmeats, packing tissue and shells at which molds will grow and possibly produce toxins is of great interest. Also of interest is the effect of lower llw levels on the survival of microorganisms on pecans during storage. llw values in pecan meats below which molds will not grow are in the range of 0.65 to 0.70. Therefore, storage of pecan meats in an atmosphere of about 70% relative humidity or below will prevent the growth of molds normally associated with pecans. It has been shown that a high quality pecan meat containing 4.3 to 4.5% moisture will, upon equilibration, result in 0.65 to 0.70 llw.

Microbiology and Sanitation I 93

The Ilw at which the pecan kernel will equilibrate depends largely on the oil content since water in the kernel will partition into the non-oil fraction. Conversely, at a given Ilw, the moisture content of pecan kernels will vary according to the oil content. This is illustrated in Figure 6.1 which shows the percentage moisture in pecans containing 63.9-76.3% oil when kernels are equilibrated to Ilw 0.68 (Beuchat 1978). There is an inverse, straight-line relationship between the moisture and oil contents. Ten pecan samples analyzed in this study represented seven different cultivars, thus accounting in part for variations in oil content and possibly for deviations from the inverse, straight-line relationship between moisture and oil contents. Differences in oil content of pecans depend greatly upon the degree of maturity when harvested. Nuts of a given cultivar that are mature and well filled have a higher oil content than those that are immature and shrunken. Thus the degree of maturity should be considered when assessing the likelihood that pecan kernels will undergo mold spoilage when moisture content is in a critical range of about 3.3 to 5.3%. Most molds will not grow at Ilw less than 0.70 and many will not grow at Ilw less than 0.80. From a practical viewpoint, the 0.70 Ilw at 25°C (77°F) criteria established by the U.S. Food and Drug Administration as a safe moisture level for nut meats appears to be outside the limits at which growth of the vast majority of molds will occur. Although certain aspergilli may grow at Ilw as low as 0.620.64 (Corry 1987), the minimum Ilw at which conidia (a specialized type of reproductive cell) of mycotoxigenic species of Aspergillus and Penicillium will genninate is reported to be 0.79 or higher at nonnal storage temperature (Mislivec, Dreter and Bruce 1975; Orth 1976). Northolt et al. (1976) reported that A. parasiticus would not produce aflatoxin at Ilw below 0.83. Limiting Ilw for growth of bacteria is higher than that for molds, ranging from 0.75 to 0.999. Only specific bacteria can grow at the low end of this Ilw range. These bacteria are not nonnally associated with pecans and thus offer limited risk to storage spoilage problems.

Sanitation and Disinfection Good sanitation practices throughout production, handling and processing are essential in order to maintain nuts of high microbiological quality. Since molds are present at all points during the development, processing and distribution of pecans, precautions should be taken at every point to insure that they do not grow. Such precautions include removal of nuts from the ground as soon as they fall from the tree, drying as quickly as possible to 4.3% moisture or less, and storing at relative humidities of 65% or less under refrigerated or frozen conditions. Whether a particular mold will grow, as well as its rate of growth on pecans, is dependent upon storage temperature and atmospheric gas composition sur-

94 / Larry R. Beuchat


,.--..... ~









.-0 (fJ












Oil (%)




Figure 6.1. Relationship between moisture and oil contents of pecan kernels adjusted to llw 0.68 at 21°C (70°F) (Adapted from: Beuchat, 1978, with permission).

rounding the nut. Molds nonnally causing spoilage of pecans have optimal growth temperatures of 20 to 35° C (68° to 95°F). At lower storage temperatures growth rates are slower and minimum ~ for growth may increase. Spoilage molds require certain levels of oxygen in the atmosphere for growth. Sealing of pecan meats under nitrogen or carbon dioxide gases would therefore retard mold spoilage, regardless of the relative humidity of the atmosphere. Destruction of bacteria and molds on pecans is accomplished to some degree through the addition of chlorine to heated soak water just prior to cracking and shelling. Because of high amounts of organic materials in the water, it is difficult to maintain chlorine at concentrations adequate to kill microbes. Additional reliance for the reduction of live microorganisms is placed on the use of propylene oxide gas. In-shell or shelled pecans are treated after the nuts are boxed and placed in large vault-like containers. Residues of 300 ppm on kernels are allowed (FDA 1981). Temperature, relative humidity and pressure within the container were controlled to assist in more effective destruction of microorganisms. Hanlin (1972) examined the efficiency of commercial propylene oxide treatments under controlled laboratory conditions and concluded that maximum allowable dosages were 80% effective in killing surface microflora and 64% effective in killing internal microflora of pecans. Low numbers of naturally 0

Microbiology and Sanitation / 95

occurring coliforms were virtually eliminated. Unfortunately, such procedures may not result in adequate reduction in viable molds and bacteria (Beuchat 1973; Blanchard and Hanlin 1973). Also, there is concern over the possible accumulation of toxic chlorohydrin compounds and propylene glycol on pecans as a result of propylene oxide treatment. The possibility of such residues is enhanced by the presence of moisture (Wesley, Rourke and Darbishire 1965; Tawaratani and Shibasaki 1972). Assuming adequate storage and marketing conditions are maintained to prevent the growth of microorganisms on pecan kernels, there is still cause for concern for the microbiological quality of the meats if they contain spores or viable cells and if they are to be incorporated into foods. Pecans may be used as ingredients in certain dairy or confectionery items without receiving pasteurization treatments beyond those administered at the shelling plant. Some of these foods have a,. high enough to support the growth of molds. For example fondants have an a,. range of 0.75 to 0.85. Fudges and grained nougats range from 0.68 to 0.75 while confectionery jellies and marshmallows may have a,. values of 0.60 to 0.76. Given the proper time/temperature conditions, molds introduced by pecans to these confections may grow. Incorporation of pecan meats into bakery products which are subjected to relatively low baking temperatures also represents a potential problem with respect to mold spoilage. Molds present on pecan meats may survive baking temperatures of 121 to 149°C (250 to 300°F). Although breads, cakes and pastries may have a,. values as high as 0.90, these products are generally consumed soon after preparation, thus minimizing chances for mold growth. Fruit cakes, however, are often prepared months in advance and stored at temperatures adequate to support the growth of microorganisms. The normal a,. range for fruit cakes is from 0.70 to 0.85. Lower a,. tends to reduce palatability. Commercial bakers and homemakers alike should recognize limitations regarding handling and storage of fruit cakes. Proper storage conditions should be provided to inhibit the growth of molds at all times. References Beuchat, L.R. 1973. Escherichia coli on pecans; survival under various storage conditions and disinfection with propylene oxide. J. Food Sci. 38:1063-1066. Beuchat, L.R. 1978. Relationship of water activity to moisture content in tree nuts. J. Food Sci .. 43:754-755, 758. Beuchat, L.R. and E.K. Heaton. 1975. Salmonella survival on pecans as influenced by processing and storage conditions. Appl. Microbiol .. 29:795-801. Blanchard, R.O. and R.T. Hanlin. 1973. Effect of propylene oxide treatment on the microflora of pecans. Appl. Microbiol.. 26:768-772.

96 I Larry R. Beuchat

Chipley, J.R. and E.K. Heaton. 1971. Microbial flora of pecan meat. Appl. Microbiol. 22:252-253. Corry, J .E.L. 1987. Relationship of water activity to fungal growth. In Food and Beverage Mycology, ed. L.R. Beuchat, pp. 51-99. New York: Van Nostrand Reinhold. Escher, F.E., P.E. Koehler and J.C. Ayres. 1973. Effect of roasting on aflatoxin content of artificially contaminated pecans. J. Food. Sci .. 38:889-892. Escher, F.E., P.E. Koehler andJ.C. Ayres. 1974. A study on aflatoxin and moldcontaminations in improved variety pecans. J. Food Sci .. 39:1127-1129. Food and Drug Administration. 1981. Part 193-Tolerances for pesticides in food administered by the Environmental Protection Agency. Title 21. Food and Drugs. Food and Drug Administration, Washington, D.C. Hanlin, R.T. 1971. Fungi isolated from young pecans. Proc. Ga Pecan Growers Assoc. 2:20-26. Hanlin, R.T. 1972. Species of Sordaria from peanut and pecan fruits. Bul. Ga. Acad. Sci .. 30:129-141. Hanlin, R.T. 1972. Unpublished data. Univ. of Georgia, Athens. Hanlin, R.T. and R.O. Blanchard. 1974. Fungi associated with developing pecan fruits. Bul. Ga. Acad. Sci .. 32:68-75. Huang, L.H. and R.T. Hanlin. 1975. Fungi occurring in freshly harvested and in-market pecans. Mycologia 67:689-700. King, A.D., M.J. Miller and L.C. Eldridge. 1970. Almond harvesting, processing, and microbial flora. Appl. Microbiol. 20:208-214. Koehler, P.E., R.T. Hanlin and L. Beraha. 1975. Production of aflatoxins BI and G I by Aspergillus fiavus and Aspergillus parasiticus isolated from market pecans. Appl. Microbiol.. 30:581-583. Krishnaswamy, M.A., N. Parthasarathy, J.D. Patel and K.K.S. Nair. 1973. Further studies on microbiological quality of cashew nut (Anacardium occidentale). J . Food Sci. Technol .. 10:24-26. Lillard, H.S., R.T. Hanlin and D.A. Lillard. 1970. Aflatoxigenic isolates of Aspergillus fiavus from pecans. Appl. Microbiol. 19:128-130. Marcus, K.A. and H.J. Amling. 1973. Escherichia coli field contamination of pecan nuts. Appl. Microbiol.. 26:279-281. McMeans, J.L. 1983. Influence of yield on in vitro accumulation of aflatoxins in pecan (Carya illinoensis (Wang.) K. Koch) nutmeats. Appl. Environ. Microbiol.. 45:714715. Meyer, M.T. 1968. The Occurrence of Escherichia coli on Black Walnut meats. M.S. Thesis, University of California, Davis. Mislivec, P.B., C.T. Dreter and V.R. Bruce. 1975. Effect of temperature and relative humidity on spore germination of mycotoxic species of Aspergillus and Penicillium. Mycologia 67:1187.

Microbiology and Sanitation I 97

Northolt, M.D., C.A.H. Verhulsdonk, P.S.S. Soentoro and W.E. Paulsch. 1976. Effect of water activity and temperature on aflatoxin production by Aspergillus parasiticus. J. Milk Food Technol. 39:170-174. Orth, R. 1976. The influence of water activity on the spore germination of aflatoxin-, sterigmatocystin- and patulin-producing molds. Lebensm. Wiss. Technol. 9:156-159. Ostrolenk, M. and H. Welch. 1941. Incidence and significance of the colon-aerogenes group on pecan meats. Food Res. 6:117-125. Schindler, A.F., A.N. Abadie, J. S. Gecan, P. B. Mislivec and P. M. Brickey. 1974. Mycotoxins produced by fungi isolated from in-shell pecans. J. Food Sci. 39:213214. Shroeder, H.W. and R.J. Cole. 1977. Natural occurrence of altemariols in discolored pecans. J. Agric. Food Chem .. 25:204-206. Shroeder, H.W. and J.B. Storey. 1976. Development of aflatoxin in 'Stuart' pecans as affected by shell integrity. HortScience 11:53-54. Tawaratani, T. and I. Shibasaki. 1972. Effect of moisture content on the microbial activity of propylene oxide and the residue in foodstuffs. J. Ferment. Technol .. 50:349. Wells, J.M., and J.A. Payne. 1976. Toxigenic species of Penicillium, Fusarium and Aspergillus from weevil-damaged pecans. Can. J. Microbiol.. 22:281-285. Wesley, F., B. Rourke and O. Darbishire. 1965. The formation of persistent toxic chlorhydrins in foodstuffs by fumigation with ethylene oxide and propylene oxide. J. Food Sci .. 30:1037.

7 Pecan Composition Charles R. Santerre


When developing food products which utilize pecans as an ingredient or component, knowledge of the composition of pecans may be useful in order to avoid undesirable interactions which may occur between pecans and other components in the food. Since pecans are lipophilic (lipid-loving) and readily absorb nonpolar flavor compounds, it would be unwise to produce a food which combines pecans with aromatic components (e.g., onions). The pecans will absorb and concentrate the flavor volatiles which may cause an objectionable flavor when eaten by the consumer. Pecans are composed of 65 to 75% lipid depending on growing conditions, maturity, variety, and past productivity of the tree. Let us discuss the composition of pecans and several factors which may affect their composition. First let's keep in mind the many uses of pecans. Figure 7.1 presents the most recent data concerning the uses of pecans in the U. S . Pecan Composition

Pecan nutritional composition is given in Tables 7.1 and 7.2 for raw and dry roasted pecan kernels. From the composition tables, it is apparent that pecans are predominantly composed of lipids. There are many factors which influence the biosynthesis of lipids in pecans. Pecans do not accumulate lipids at a constant rate during growth in the orchard. Wood and McMeans (1982) reported that pecans grown in central Georgia have a dramatic increase in lipid biosynthesis during early September which is approximately one month prior to harvest for this region. The dramatic increase in lipid biosynthesis lasts for approximately two to three weeks. Thus, environmental conditions including drought, excessive rain, excessive winds, reduced photo period, or damage due to insects, birds, C. R. Santerre (ed.), Pecan Technology © Chapman & Hall, Inc. 1994


Pecan Composition / 99 Others e.real Manufacturers Exports Gift Packers Other Shellers & Processors 1m;;;;;;;;;;'"


Other Food Manufacturers




Mixers and Salters


Ice Cream Manufacturers



Ii Ul

'lrocery Wholesalers Rack Jobbers

Confectioners : )(,


Mail Order Bakers ,,," '..





Gift Packers/Mail Order




Grocery & Wholesalers Shellers Processors


~ .c




'==~Bg J o





Percent Distributed in U.S.

Figure 7.1.

U.S. Distribution of Pecans (adapted from USDA 1983-84)

rodents or molds which occurs during lipid biosynthesis may affect the development of pecans. Significant research has been conducted to determine the lipid composition of pecans. Senter and Horvat (1978) detected 23 fatty acids in pecans. These include the following acids: decanoic (C lO:0 ), dodecanoic (C I2 :0 ), dodecenoic (C I2 :1), tetradecanoic (C I4:0 ) , tetradecenoic (C I4 :1), tetradecadienoic (C I4 :2), pentadecanoic (C I5 :0 ), pentadecenoic (15:1), pentadecadienoic (C IS :2)' hexadecanoic (C I6 :0 ), hexadecenoic (C I6 :1), hexadecadienoic (C I6 :2 ), heptadecanoic (C 17 :o), heptadecenoic (C 17 : I ), heptadecadienoic (C I7 :2), octadecanoic (C I8 :0), octadecenoic (C I8 :1), octadecadienoic (C I8 :2), octadecantrienoic (C IS:3), eicosanoic (C 20:0), eicosenoic (C 20: 1) , eicosandienoic (C20:2), and heneicosanoic (C 21 :0). Beuchat and Worthington (1978) found for pecans with 70.3% lipid, the distribution of fatty acids was: C 16:0 (5.7%), C 16: 1 (0.11%), C 17:o (trace), C I8 :o (2.2%), C 18: 1 (66.9%), C 18:2 (22.1%), C 18 :3 (1.1 %), C2o:o (0.21 %), and C 20: 1 (0.39%). From this data, it is apparent that the lipids in pecans are primarily unsaturated fatty acids (90.6%) which includes a high percentage of polyunsaturated fatty acids (23.6%). A comparison of 14 dietary sources of lipid is presented in Figure 7.2. Pecan oil is very low in saturated fat. Only canola and safflower oils are lower. Pecan oil is also high

100 / Charles R. Santerre Table 7.1.

Nutrients in raw pecans (100 grams) (USDA 1984).

Calories Water Protein Carbohydrates Dietary Fiber Lipid-Total Lipid-Saturated Lipid-Monounsaturated Lipid-Polyunsaturated Cholesterol Vitamin A-Carotene Vitamin A-Preformed Vitamin A-Total Thiamin Riboflavin Niacin

667 4.82 g 7.75 g 18.2 g 1.6 g 67.7 g 5.42g 42.2 g 16.8 g Omg 12.8 REa ORE 12.8 RE 0.848 mg 0.128 mg 0.887 mg

Essential Amino Acids Isoleucine 0.322 g Leucine 0.520 g Lysine 0.292 g Methionine 0.186 g Phenylalanine 0.409 g Threonine 0.253 g Tryptophan 0.199 g Valine 0.386 g



Pyridoxine-B6 Cobalamin-BI2 Folacin Pantothenic acid Vitamin C Vitamin E Calcium Copper Iron Magnesium Phosphorus Potassium Selenium Sodium Zinc

0.188 mg

o J.Lg

39.2 J.Lg 1.70 mg 2.00 mg 3.15 mg 0.036 g 1.19 mg 2.13 mg 0.128 g 0.291 g 0.392 g 5.09 J.Lg 0.926 mg 5.47 mg

Nonessential Amino Acids Cysteine 0.209 g Tyrosine 0.284 g Arginine 1.1 05 g Histidine 0.227 g Alanine 0.338 g Aspartic Acid 0.708 g Glutamic Acid 1.545 g Glycine 0.377 g Proline 0.360 g Serine 0.376 g

retinol equivalents

in monounsaturated fatty acids and is exceeded only by olive oil. Current dietary recommendations in the U.S. include reducing total calories obtained from fat from 42 to 30% while increasing calories from carbohydrates (especially complex carbohydrates) from 46 to 58% (Santerre 1990). Additionally, the recommendation was to reduce saturated fat and increase polyunsaturated fat intake. Pecans, like many foods, can be an integral part of a healthy diet. Heaton, Marion and Woodroof (1966) measured the primary lipids of 45 varieties from six growing locations to determine the influence of geographical growing location (Table 7.3) on lipid composition. Their findings indicate that small variations in pecan composition can be found due to growing location. However, they found a greater influence from nitrogen fertilizer application on fatty acid distribution (Table 7.4) than was found for location. Pecan trees which received low levels of nitrogen for nine-years had a significantly higher concentration of C ISI ' but a significantly lower concentration of C IS :2 • Total lipid accumulated was not significantly influenced by the level of fertilizer applied. The influence of variety on fatty acid composition has been reported by numer-

Pecan Composition / 101 Table 7.2.

Nutrients in dry-roasted pecans (100 g) (USDA 1984).

Calories Water Protein Carbohydrates Dietary Fiber Lipid-Total Lipid-Saturated Lipid-Monounsaturated Lipid-Polyunsaturated Cholesterol Vitamin-A-Carotene Vitamin A-Preformed Vitamin A-Total Thiamin Riboflavin Niacin

659 1.10 g 7.97 g 22.3 g 1.66 g 64.6 g 5.18 g 40.2 g 16.0 g Omg 12.3 REa ORE 12.3 RE 0.317 mg 0.123 mg 0.905 mg

Essential Amino Acids Isoleucine 0.331 g Leucine 0.535 g 0.301 g Lysine Methionine 0.191 g 0.421 g Phenylalanine Threonine 0.260 g Tryptophan 0.205 g Valine 0.397 g

Pyridoxine-B. Cobalamin-BIz Folacin Pantothenic acid Vitamin C Vitamin E Calcium Copper Iron Magnesium Phosphorus Potassium Selenium Sodium Zinc

0.176 mg


4O.81Lg 1.75 mg 2.05 mg 3.11 mg 0.Q35 g 1.24 mg 2.18 mg 0.134 g 0.303 g 0.370 g 11.7 ILg 0.704 mg 5.67 mg

Nonessential Amino Acids Cysteine 0.215 g Tyrosine 0.292 g Arginine 1.137 g Histidine 0.233 g Alanine 0.347 g Aspartic Acid 0.728 g Glutamic Acid 1.590 g Glycine 0.388 g Proline 0.370 g 0.387 g Serine

"RE = retinol equivalents

ous researchers (Senter and Horvat 1976; Heaton, Marion and Woodroof 1966; French 1962). These data have been combined in Table 7.5. Variations within a variety appear to be greater than variations between varieties. Fatty acids are generally found in pecans in the form of triglycerides (i.e., three fatty acids attached to a glycerol backbone), as diglycerides (i.e., two fatty acids attached to a glycerol backbone), as monoglycerides (i.e., one fatty acid attached to a glycerol backbone), or as phospholipids (i.e., one or two fatty acids plus a phosphorylated form of choline, serine, inositol, or ethanolamine, attached to a glycerol backbone). Other lipids found in pecans include sterols which are found in low concentrations. Senter and Horvat (1976) reported on the complex lipids for six varieties (Table 7.6). Triglycerides composed 95% of the lipids present in pecans. Carbohydrates are the next most prevalent constituent of pecans. Pecans are composed of 18.2% carbohydrates, of which 1.6% is dietary fiber (Tables 7.1 and 7.2). Fourie and Basson (1990) found total sugars to be 0.02% of pecans with sucrose (20.2 mglg), fructose (0.2 mg/g), glucose (0.1 mglg) and inositol

102 / Charles R. Santerre 100

.. ..




:. -o

r----------;::::::::::========::::;----, •

Saturated Fat


Polyunsaturated Fat


Monounsaturated Fat






• :;; •c !• A-• 0• Ii ••• •






. • i: •

.2 :::I


c (;





•• .a >0




•• A-

"•• •c






• A-

.. I-






~ ;

.. :::I

c 0

u 0 0




Dietary Source of Lipid Figure 7.2.

Composition of 14 dietary sources of lipid (adapted from USDA).

(0.1 mg/g) as the primary sugars. Wood and McMeans (1982) found the total sugars to be at a maximum concentration of 320 mg/g (0.3%) by early August for pecans growing in middle Georgia which decreases to approximately 21 mg/ g (0.02%) by mid-September. Part of the decrease in percent total sugars can be attributed to a dramatic increase in total lipids in developing pecans during early-September. The last major component of pecans is proteins which comprise 7.75% of the kernel. Amino acid compositions of raw and dry-roasted pecans are given in Tables 7.1 and 7.2. Chemical score for amino acids in pecans is presented in Table 7.7. Chemical score is a method for comparing a protein source to a standard protein sources for its ability to promote growth in developing test animals. Egg protein is generally considered to be a good source of proteins and is often used as a standard for comparison because it is considered to have the best ratio of essential amino acids which are required for protein synthesis. The essential amino acid(s) which is/are found to have the lowest chemical score is/

Pecan Composition / 103 Table 7.3.

Fatty acid oj pecans from different growing locations.



Oil (%)




C IS,2

C IS,3

76.3 74.2 73.6 72.8 71.6 61.5

5.9 5.5 6.0 5.8 5.8 5.4

2.6 2.4 2.2 2.2 2.2 2.2

63.5 69.3 64.7 64.4 60.5 67.3

25.6 21.7 25.5 26.1 29.7 23.9

1.6 1.2 1.7

1.5 1.6 1.3

Adapted from Heaton, Marion and Woodroof (1966).

are considered to be the most limiting for optimal protein synthesis. For pecans, lysine is the limiting essential amino acid in pecans since it has the lowest chemical score (i.e., 37-46) for the five varieties examined. Micro-nutrients in pecans include vitamins and minerals and are presented in Tables 7.1 & 7.2. Senter (1976) reported the concentration of 16 minerals in 10 pecan varieties (Table 7.8). The levels of calcium reported by Senter (1976) are dramatically lower than given by the USDA (1984), while the levels of phosphorus arehigher. Varietal differences, growing locations, sample size and analytical methods may be possible reasons for these discrepancies. The vitamins found in pecans include thiamin, riboflavin, niacin, pyridoxine, folacin, pantothenic acid, ascorbic acid, tocopherols and precursors to retinol (i.e., carotenoids) (Tables 7.1 & 7.2). Senter (1975) reported on carotenoid composition in pecan kernels for 10 varieties (Table 7.9). Significant varietal differences were only detected for dihydroxyxanthophylls for the varieties examined. Lambertsen, Myklestad and Braekkan (1962) reported a- and ')I-tocopherol concentrations in pecans to be 1.5 and 17.0 mg/loog oil, respectively. Yao (1990) reported the concentration of a, f3, ')I, and 8-tocopherols in eight pecan varieties (Table 7.10). ')I-tocopherol ranged from 20.8 to 30.0 mg/100 g pecan, a-tocopherol ranged from 0.9 to 1.6 mg/loo g pecan, and f3- and 8-tocopherols ranged from 0.1 to 0.3 mg/loo g pecan. Fourie and Basson (1989) found total tocopherol in pecans to be 19.2 mg/loog oil with a-tocopherol concentration ranging from 12.3 to 17.4 mgt 1oog oil. They found that total tocopherol concentration decreased from 19.2 to 17.5 mg/loog oil during four months of storage Table 7.4.

Effect oJ nitrogen Jertilization on the Jatty acid composition oJpecans.


Oil (%)

C I6,O



C IS,2

C IS,3

Low Nitrogen Medium Nitrogen High Nitrogen

71.0 67.8 67.3

6.1 6.7 6.7

0.7 1.0 1.2

65.1 60.8 56.9

27.3 31.0 34.4

0.9 0.7 0.9

Adapted from Heaton, Marion and Woodroof (1%6).

104 I Charles R. Sante"e Table 7.5.

Falty acid composition of pecan varieties. Percent of Total Lipid






'BigZ" 'Cheyenne,3 'Curtis" 'Curtis' 2 'Desirable,2 'Elliot' 2 'Farley,2 ,Frotscher" 'Mahan,2 'Mahan,3 'Mobile" 'Moneymaker" 'Moneymaker,2 'Moore,2 'Pabst' 2 'Randall" 'Schley,2 'Schley' x 'Barton' 3 'Schley' x 'McCulley,3 'Seedling I" 'Seedling 2" 'Shoshoni,3 'Stuart" 'Stuart,2 'Stuart' 3 'Success" 'Success,2 'Teche" 'VanDeman"

5.9 6.0 6.1 5.8 4.9 6.4 5.4 6.5 5.9 5.8 7.1 6.3 6.5 5.8 5.5 6.0 6.2 5.5

t 0.5








4.3 6.3 5.0 6.6 6.1 5.7 5.4 5.5 6.1 5.1







59.7 48.5 71.8 59.1 71.0 62.6 66.5 63.9 57.3 49.2 56.8 51.0 64.2 67.2 61.9 61.3 64.2 54.6

30.3 34.3 18.1 28.4 20.9 27.0 24.6 25.5 32.4 31.5 31.4 37.8 25.9 23.4 28.2 28.2 26.3 28.4

1.6 1.7 0.8 1.8 1.2 1.8 1.3 1.3 1.9 2.4 1.8 1.7 1.5 1.2 2.0 1.5 1.2 1.9

0.4 0.5 0.1



2.9 3.5 3.1 2.4 2.0 2.1 2.2 2.5 2.4 2.7 2.7 2.6 2.0 2.3 2.3 2.9 2.0 1.9










3.9 3.2 1.9 2.2 2.1 1.7 2.9 2.3 3.0 2.9

69.2 71.0 55.0 68.8 62.9 50.1 76.5 68.0 63.4 74.6

21.2 18.5 28.0 21.0 27.3 32.6 13.5 23.2 25.7 16.0

1.3 0.9 2.4

0.3 t 0.6






0.7 0.4






0.2 1.0 0.2 0.4



1.7 2.6 1.3 1.0 1.3 0.9


0.6 0.4

0.8 0.2 0.6


'French (1962). 2Heaton, Marion and Woodroof (1966). 3Senter and Horvat (1976). 4

t = trace.

at 30°C (86°F), 55% ERH when pecans were found to have turned rancid. Yao measured changes in tocopherols during storage of pecans for 48 weeks at 23. 9°C (73°F), 60-70% ERH. Significant reductions were observed in the 'Y-tocopherol concentrations in 'Desirable' and 'Schley' pecans but not for 'Stuart' pecans during storage (Figure 7.3). There were no significant changes in the concentrations of other tocopherols. Tocopherols may be an important naturally-occurring

Pecan Composition / 105 Table 7.6.

Lipid content of selected pecan varieties (Senter and Horvat 1976). Concentration (g/IOO g pecan)" OC, 0:'ex,{3Lipid monoContent Complex glyceride diglyceride diglyceride Sterol Triglyceride

Cultivar 'Stuart' 'Mahan' 'Cheyenne' 'Shoshoni' 'Schley' x 'Barton' 'Schley' x 'McCulley' Means

0.48 0.30 0.17 0.50 0.50 0.35 0.38

72 74 75 72 74 72 73

0.79 0.55 0.27 1.17 0.54 0.52 0.64

0.79 0.75 0.05 0.30 0.70 0.59 0.53

0.33 0.18 0.02 0.43 0.24 0.09 0.22

0.21 0.15 0.07 0.30 0.17 0.08 0.16

69.39 72.07 74.41 69.32 71.91 70.38 71.25

"dry weight basis

antioxidant in pecans in addition to being an important nutrient (Vitamin E) for humans. Phenolic acids are a broad class of compounds which are naturally occurring in pecans and have been associated with astringent flavor, color changes, inhibitor of enzymatic activity and antioxidant effects (Senter, Horvat and Forbus 1983). Senter, Horvat and Forbus (1980) studied eight phenolic acids in the testa of pecans to determine changes in these acids during pecan storage (Figure 7.4). During 12 weeks of storage at 21°C (70°F), 65% ERH, pecan sensory scores and the concentration offourphenolic acids (gallic, gentisic, vanillic, and protocatechuic acids) decreased. Two phenolic acids (coumaric and syringic acids) were present in only trace amounts which did not change during storage and two Table 7.7.

Chemical score for amino acids in pecans grown at three locations. Chemical Score (% of amino acids found in eggs)

Essential Amino Acid Lysine Methionine Phenylalanine Leucine Isoleucine Threonine Valine Tryptophan


'Moneymaker'2 'Schley,2 'Schley" 'Sioux" 'Sioux" 'Stuart'2 'Stuart,3


56 89 70 61 61 65 100

45 59 93 70 64 61 63 100

Adapted from Meredith (1974). 'Grown at Brownwood, TX. 2Grown at Byron, GA. 3Grown at Albany, GA.

37 62 78 64 59 55 56 100

45 59 78 68 63 61 62 100

37 59 78 64 59 55 58 100

39 65 78 58 54 55 53 100

37 56 74 58 54 53 53 100

42 59 80 62 59 55 58 100

Table 7.B.

Mineral composition (mgI100 g) for 10 pecan cultivars (Senter 1976).










'Cheyenne' 'Western' 'Tejas' 'Cherokee' 'Schley' x 'Barton' 'Shoshoni' 'Stuart' 'Schley' x 'McCulley' 'Mahan' 'Desirable' Mean

1.44 1.22 1.22 1.l0 1.09 1.06 1.08 0.90 0.87 0.82 1.08

1.93 2.52 2.65 2.41 2.15 2.28 2.02 2.00 2.11 1.93 2.20


0.11 0.15 0.13 0.20 0.13 0.16 0.16 0.15 0.00 0.00 1.20

0 0 0 0 0 0 0 0 0 0 0

2.42 4.39 1.85 1.73 4.83 3.11 2.21 5.33 2.97 3.99 3.28

0.57 0.42 0.90 0.74 0.63 0.52 0.63 0.63 0.32 0.80 0.62

5.60 8.21 7.18 8.03 5.30 6.26 8.16 5.65 5.40 10.40 7.02









0.07 0.08 0.05 0.07 0.07 0.05 0.06 0.08 0.07 0.05 0.06

0.52 0.53 0.74 0.64 0.52 0.57 0.58 0.52 0.53 0.69 0.58

0.67 0.63 0.90 0.32 0.47 0.41 0.48 0.63 0.27 0.80 0.56

0.00 0.63 0.21 0.84 0.21 0.62 0.00 0.84 0.63 0.42 0.44

390 430 470 430 440 500 470

330 370 440 540 390 490 470 430 440

0.00 5.30 5.30 0.00 5.30 5.20 0.00 10.50 5.30 21.20 5.80

140 130 160 150 150 160 120 120 170 170 140

'Cheyenne' 'Western' 'Tejas' 'Cherokee' 'Schley' x 'Barton' 'Shoshoni' 'Stuart' 'Schley' x 'McCulley' 'Mahan' 'Desirable' Mean

400 340 610 450



at = trace

Table 7.9. Mean concentration (Il-glg lipid) of lipids and carotenoids in pecans (Senter 1975). Xanthophylls


Total Carotene




Total Carotenoids

'Shoshoni' 'Schley' x 'Barton' 'Mahan' 'Western' 'Desirable' 'Schley' x 'McCulley' 'Cheyenne' 'Tejas' 'Cherokee' 'Stuart'

0.197 0.296 0.140 0.309 0.292 0.150 0.201 0.272 0.111 0.094

0.246 0.138 0.177 0.219 0.187 0.177 0.290 0.232 0.265 0.213

0.262 0.257 0.237 0.234 0.160 0.100 0.058 0.055 0.054 0.Ql8

0.681 0.503 0.576 0.745 0.687 0.715 0.854 0.684 0.570 0.572

1.386 1.194 1.130 1.507 1.326 1.142 1.403 1.243 1.000 0.897


Table 7.10.

Tocopherol concentration (mgllOOg pecan) in eight pecans cultivars.







'Cape Fear' 'Desirable' 'Cheyenne' 'Stuart' 'Sumner' 'Schley' 'Eastern Wichita' 'Western Wichita'


0.2 0.2 0.3 0.2 0.2 0.2 0.2 0.2

24.4 25.9 30.0 23.7 24.1 24.7 21.0 20.8

0.2 0.3 0.2 0.1 0.2 0.2 0.1 0.1

25.9 28.0 31.6 25.2 25.4 25.9 22.5 22.1

1.6 1.3 1.2 0.9 0.9 1.2 1.0

Adapted from Yao 1990.

C as







25~~~~qr~~~ 20







.c Q. o CJ o





• •

'Stuart' Pecans 'Desirable' Pecans 'Schley' Pecans



as E E as









Storage Time (weeks) Figure 7.3. 'Y- Tocopherol concentration for three pecans varieties during storage at 23.9°C (73°F), 60-70% ERH (adapted from Yao 1990).


108 I Charles R. Santerre













Gallic acid

Gentisic acid Vanillic acid Protocatechuic acid



C) C)



-. 0
















Storage Interval (weeks) Figure 7.4. Changes in selected phenolic acids during pecan storage at 21 °C(70°F), 65% ERH (adapted from Senter, Horvat and Forbus 1980).

other phenolic acids (p-hydroxy benzoic and phenlyacetic acids) did not change significantly during storage. The authors theorized that phenolic acids in the testa (skin) may provide some protection from oxidation for the kernel. At present, there is only an association between rancid flavor development and loss of phenolic acids in the testa. In addition to naturally occurring compounds in pecans, consideration should be given to compounds which are formed during the roasting of pecans. Wang and Odell (1972) detected 19 carbonyls, 8 pyrazines, 7 acids, 5 alcohols, a lactone and pyridine by GClMS analysis of steam distillate from ground pecans (Table 7.11). Due to the heating during distillation of the pecan volatiles, many of the carbonyl compounds may have resulted from the breakdown of the longchain fatty acids. The researchers detected all of the carbonyls listed in Table 7.11 in raw pecans with the exception of furfural and 2,3-pentanedione. Wang and Odell (1973) further attributed the formation of pyrazines to chemical changes which occur during the heating of certain amino-hydroxy compounds (i.e., etha-

Pecan Composition / 109 Table 7.11. Compounds present in roasted pecans (Wang and Odell 1972). Carbonyls ethanal propanal butanal pentanal hexanal heptanal octanal 2-hexenal 2-heptenal 2-decenal 2-undecenal acrolein 2,4-heptadienal 2,4-decadienal Acids acetic acid propionic acid pentanoic acid 4-methyl pentanoic acid hexanoic acid heptanoic acid octanoic acid pyridine

Pyrazines 2-methylpyrazine 2,5-dimethylpyrazine 2,6-dimethylpyrazine 2,3-dimethylpyrazine 2-ethyl-6-methylpyrazine 2-ethyl-5-methylpyrazine 2,3,5-trimethylpyrazine Alcohols ethanol l-pentanol I-hexanol I-heptanol l-octanol Lactone 'Y-octalactone

nolamine, glucosamine, serine, threonine, 4-amino-3-hydroxybutyric acid and alanylserine) in contrast to early studies which suggested the pyrazines were fonned only when sugars and amino acids were heated. To summarize, lipids are the primary component of dried pecans and playa significant role in their shelf-life during storage. Lipids contribute significantly to the mouth-feel and flavor of pecans. Approximately 90% of the fatty acids in pecans is unsaturated and 95% of the fatty acids occur in triglycerides. Variations in lipid distribution can result from variety, cultural conditions, maturity and past productivity of the pecan tree. Pecans are limiting in the essential amino acid, lysine, but are composed of about 8% protein. Pecans are also composed of numerous micronutrients (i.e., vitamins and minerals) in addition to lipids and proteins. References Beuchat, L.R., and R.E. Worthington. 1978. Technical note: fatty acid composition of tree nut oils. Journal of Food Technology. 13:355-358. Fourie, P.C., and D.S. Basson. 1989. Changes in the tocopherol content of almond,

110 / Charles R. Santerre pecan and macadamia kernels during storage. Journal of the American Oil Chemists Society. 66(8):1113-1115. Fourie, P.e., and D.S. Basson. 1990. Sugar content of almond, pecan, macadamia nuts. J. Agric. Food. Chem. 38:101-104. French, R.B. 1962. Analyses of pecan, peanut, and other oils by gas-liquid chromatography and ultra-violet spectrophotometry. Journal of the American Oil Chemists Society. 39:176--178. Heaton, E.K., J.E. Marion, and J.G. Woodroof. 1966. Pecan oil is highly unsaturated. Peanut Journal and Nut World. 45(12):36--38. Lambertsen, G., H. Myklestad, and O.R. Braekkan. 1962. Tocopherols in nuts. J. Sci. Food Agric. 13:617-620. Meredith, F.I. 1974. Amino acid composition and quality in selected varieties of pecans Carya iIIinoensis. Proceedings of the Florida State Horticultural Society. 87:362-365. Santerre, e.R. 1990. Compositional, nutritional value of pecans. The Pecan Grower. 1(5):13. Senter, S.D. 1975. Carotenoids of pecan nutmeats. HortScience. 10(6):592. Senter, S.D. 1976. Mineral composition of pecan nutmeats. Journal of Food Science. 41:963. Senter, S.D. and R.J. Horvat. 1978. Minor fatty acids from pecan kernel lipids. 43(5):1614. Senter, S.D., R.J. Horvat, and W.R. Forbus Jr. 1983. Comparative GLC-MS analysis of phenolic acids of selected tree nuts. Journal of Food Science. 48:798-799. Senter, S.D. and R.J. Horvat. 1976. Lipids of pecan nutmeats. Journal of Food Science. 41:1201-1203. Senter, S.D., Horvat, R.J., and Forbus Jr, W.R. 1980. Relation between phenolic acid content and stability of pecans in accelerated storage. Journal of Food Science. 45: 13801382. United States Department of Agriculture. 1984. Composition of Foods: Nut and Seed Products. Agriculture Handbook No. 8-12. Wang, P.S. and G.V. Odell. 1972. Characterization of some volatile constituents of roasted pecans. Journal of Agriculture and Food Chemistry. 20(2):206--210. Wang, P.S. and G.V. Odell. 1973. Formation of pyrazines from thermal treatment of some amino-hydroxy compounds. Journal of Agriculture and Food Chemistry. 21(5):868-870. Wood, B.W. and J.L. McMeans. 1982. Carbohydrates and fatty acids in developing pecan fruit. Journal of Amer. Soc. Hort. Sci. 107(1):47-50. Yao, F. 1990. HPLC quantification of tocopherols in pecans and the relationship of tocopherol levels during storage to pecan kernel quality. Ph.D. Dissertation, University of Georgia, Athens, GA.

8 Methods for Measurement of Pecan Quality Marilyn C. Erickson


Quality, as defined by Kramer and Twigg (1970), is "the composite of those characteristics that differentiate individual units of a product, and have significance in determining the degree of acceptability of that unit by the buyer." Consequently, to maintain quality in a product, those characteristics must first be individually identified. In the case of pecan quality, however, different segments of the pecan industry have identified and emphasized different characteristics (Hubbard, Florkowski and Purcell 1990). Both growers and accumulators considered meat yield to be the dominant quality factor with count and color ranking second and third. Shellers, on the other hand, ranked color as their primary quality factor, while meat yield and minimal damage ranked second and third. In contrast, shellers contend that their buyers do not consider meat yield an important quality factor. According to shellers, primary emphasis is placed on size by bakers, confectioners, gift pack trade and service outlets while ice cream manufacturers place primary emphasis on both size and minimal foreign material, and retail grocers and wholesale distributors place primary emphasis on color. Once quality attributes are identified, differentiation as to the degree of acceptability for that attribute will enable pecans to be classified into different grades of varying value. Any classification scheme, though, is dependent on the ability to accurately measure these attributes. This chapter will therefore briefly introduce the concepts of grades and standards, then concentrate on describing methods used to measure physical, sensory, compositional and microbiological quality attributes of pecans.

C. R. Santerre (ed.), Pecan Technology © Chapman & Hall, Inc. 1994


112 / Marilyn C. Erickson

Grades and Standards In general, grades and standards are introduced to facilitate the flow of market information from a commodity buyer to a commodity producer. A buyer who purchases pecans based on defined grades and standards thus conveys to the seller the desired quality of pecans that are willing to be bought at a given price. Several institutions have established grades and standards for pecans. In 1969, the U.S. Department of Agriculture (USDA) published standards for grades of shelled pecans (USDA, 1969) and in 1976 for in-shell pecans (USDA 1976). In 1980, a booklet was published describing the standards established by the Federated Pecan Grower's Association (FPGA) and USDA Food Safety and Quality Service (FPGA 1980). More recently, a fourth set of guidelines has been prepared by the National Pecan Shellers and Processors Association (NPSPA) in cooperation with the U.S. Food and Drug Administration. Tables 8-1 and 8-2 display the requirements for classification of shelled pecans into the various grades, U.S. No.1 Halves, U.S. No.1 Halves and Pieces, U.S. No.1 Pieces, U.S. Commercial Halves, U.S. Commercial Halves and Pieces and U.S. Commercial Pieces, that have been specified by USDA (1969). The Table B.1.

Grade classification of shelled pecans.

Quality Characteristics

No. I Halves

Commercial No. I Halves! No. I Commercial Halves! Commercial Pieces Pieces Pieces Pieces Halves

(I) well dried (kernel firm and crisp, not pliable or leathery) Yes Yes Yes (2) fairly well developed (kernel has at least a moderate amount of meat in proportion to its width and length) Yes Yes Yes (3) requirement for being fairly uniform in color (~ 90% with skin color in I or 2 classifications) Yes Yes No (4) allowed proportion of defects with serious injury sO.5% sO.5% sO.5% (5) total tolerance in categories (I), (2), (3) & (4) s3% s3% s3% (6) portion of kernels having "dark amber" skin color s3% s3% s3% (7) wt. of shell pieces, center sO.05% sO.05% sO.05% wall & foreign material Adapted from USDA (1%9).






















Methods for Measurement of Pecan Quality / J13 Table 8.2.

Grade classification of shelled pecans.

Size Characteristics

No. 1 Commercial No. 1 Halves/ No. 1 Commercial Halves/ Commercial Halves Pieces Pieces Halves Pieces Pieces

(1) requirement for uniformity in size of halves


No Yes

100% 100%



~95% ~95%




(2) ~50% half-kernels (3) half kernels conform to size classification

Yes Yes

(4) halves conform to exact count (halves/pound) if specified

(5) comply with tolerances for undersize

(6) comply with tolerances for off-size (7) no passage through


Yes Yes s15% s15%

Yes s15%

Yes s15%





Adapted from USDA (1969).

size of halves are specified according to the number of halves per pound (Table 8.3) whereas pieces are classified following a sieve test (Table 8.4). Tolerances for sizes of shelled pecan pieces are given in Table 8.5. Grades for in-shell pecans, U.S. No. I and U.S. No.2, which have been specified by USDA (1976), are described in Table 8.6 while the USDA size classifications are given in Table 8.7. Additional details on requirements and definitions of terms for both in-shell and shelled pecans may be found in the USDA (1969, 1976) publications. Despite the existence of pecan grades and standards, much concern exists in the industry regarding growers' ignorance of these guidelines and buyers' apparent inconsistency in following these guidelines. Readily apparent in the USDA grades and standards is the heavy reliance on subjective evaluation of color and fill size. To remove this subjectiveness, future specifications, particularly of color, should Table 8.3.

Size classifications for shelled pecan halves. Number



Mammoth Junior Mammoth Jumbo Extra large Large Medium Small (topper) Midget



251-300 301-350 351-450 451-550 551-650 651-750 >750

552-660 662-770 772-990 992-1210 1212-1430 1432-1650 >1652

Adapted from USDA (1969).


114 / Marilyn C. Erickson Table 8.4.

Size classifications for shelled pecan pieces. Diameter Hole to Pass Through







Extra large

7/16 to 5/16 to 3/16 to 2116 to 1116 to 1116 to

Large Medium Small Midget Granules

9/16 8/16 6116 4/16 3/16 2116

10.9 to 7.8 to 4.7 to 3.1 to 1.6 to 1.6 to

14.1 12.5 9.4 6.3 4.7 3.1

Adapted from USDA (1969).

be expressed in objective units that would be obtained from colorimetric instrumentation. Modifications in grades and standards will, however, require input from all segments of the pecan industry.


A critical area for consideration in measurement of quality attributes is the number of samples which would be considered representative of the lot. Recommendations reported by Rorkowski and Hubbard (1991) are one pound (0.46 kg) for each 1000 pounds (450 kg) delivered or 10% of the sample if present in bags. The USDA (1976), alternatively, recommended a 100 nut sample size, however, the number of 100-count samples, which would vary with the lot size, was not given.

Table 8.5.

Tolerancesfor sizes of shelled pecan pieces. Tolerances (%)


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