CHAPTER 8

NUTS

Many temperate broad-leaved trees produce a fruit that is hard and oily, commonly known as a nut. As is the case with soft textured fruits, the nuts of many temperate broad-leaved trees are important food sources, and some produce edible oils. Several species of nuts are used for a variety of industrial products. Some nut crops of temperate broad-leaved trees, including English or Persian walnuts (Juglans regia), pecans (Carya illinoinensis), pistachios (Pistacia spp.) and hazel or filberts (Corylus spp.), are produced in orchards and are considered to be agricultural rather than forest crops. As was done in Chapter 7, emphasis is placed on those nuts that are gathered, at least to some degree, in natural or planted forests (Figure 8.1).

Figure 8.1 A dried fruit and nut market in Quetta, Balochistan Province, Pakistan. Most of the products sold here are from temperate broad-leaved trees. While many of these products are grown in orchards as agricultural crops, others are still gathered in natural or planted forests.

ACORNS

Acorns, the nuts of oaks and related trees (Figure 8.2) have a variety of uses. They have provided a staple food for humans and have been used as feed for livestock. The acorns from most oaks are also an important food for wild game and other wildlife species. Moreover, several species of acorns have been used as a source of natural dyes.

Figure 8.2 - Acorns of Quercus aegilops, an oak indigenous to the Mediterranean region of Europe. Isle of Naxos, Greece

HUMAN CONSUMPTION

Acorns have been a traditional food source for many human societies (Table 8.1). They are a source of vitamin C and starch and are reported to be high in magnesium, calcium and phosphorus. When compared to barley and wheat, acorns are slightly lower in carbohydrates and protein content but are higher in fat and fibre content. Therefore they have a higher caloric content per unit weight (average 4 994 calories/kg) than cereal grains. Unfortunately, acorns are also high in tannin content. Tannin imparts a bitter, astringent flavour to the nuts but is easily leached. Acorns have been eaten raw, roasted or boiled. In parts of the American Midwest and Europe, a coffee-like beverage has been made from acorns. Acorn oil is used for cooking in parts of North Africa and acorns have been used for medicinal salves and cooking by the indigenous tribes in eastern North America [Bainbridge, 1986; Burns and Honkala, 1990; Derby, 1980; Wickens, 1995].

Acorn production varies from year to year and in good years can reach levels of 3 000-6 000 kg/ha/a. Individual, open grown trees, e.g. Oregon white oak (Quercus garryana) can produce several hundred kilograms in a single growing season [Bainbridge, 1986].

Among their most widespread uses, acorns were used as a staple food by the indigenous tribes of California, who worshipped both the acorn and the oak. Acorns may have been an important food source as early as 5000 BC [Schneider, 1990]. The importance of acorns to these cultures is recorded in the journals of John C. Fremont in his historical second California expedition of 1844 [Peattie, 1953]:

“....an Indian village, consisting of two or three huts; we had come upon them suddenly, and the people had evidently just run off. There huts were low and slight, made like beehives in a picture, five or six feet high, and near each was a crate, formed of interlaced branches and grass in size and shape like a very large hogshead. Each of these contained from six to nine bushels. These were filled with long acorns already mentioned, and in the huts were several neatly made baskets containing quantities of the acorns roasted. They were sweet and agreeably flavoured, and we supplied ourselves with about half a bushel, leaving one of our shirts, a handkerchief and some smaller articles in exchange.”

The native vegetation of the foothills of the Sierra Nevada Mountains and coast ranges and the riparian zones of the Central Valley was composed of extensive woodlands and savannahs dominated by several species of oak (Figure 8.3). It is estimated that about 230 kg of acorns per person per year was consumed by indigenous hunter-gatherers. Acorns from a number of species of oaks were used including Q. agrifolia, Q. douglasii and Q. kelloggi. These tribes made extensive use of fire for a variety of purposes, including making acorn gathering easier. Oak woodlands were typically burned just prior to the time acorns ripened and fell from the trees. The frequent use of fire by these tribes helped to maintain open oak woodland [Burns and Honkala, 1990; Rossi, 1990]

Figure 8.3 A grove of blue oak (Quercus douglasii) in the Coast Range of California. The acorns of this and many other North American oaks provided a staple food source for indigenous tribes.

Indigenous tribes in other parts of the western United States also made extensive use of acorns. The area once dominated by the Apaches, which consisted of western Texas, New Mexico and Arizona in the United States and northern Sonora in Mexico, coincides almost exactly with the natural range of Quercus emoryi. The acorns of this oak were ground into a sweet-tasting meal and were often eaten raw [Peattie, 1953]. The Kalapuya tribe of the Willamette Valley of Oregon used the acorns of Q. garryana as a staple food source and, like their counterparts in California, used fire to clear competing vegetation and make acorn gathering easier [Boyd, 1986]. The indigenous tribes along the Columbia River of Oregon and Washington used urine to cure acorns, which later became known as “chinook olives” by the first European-American settlers in the region.

Acorns are still an important food source in many parts of the world, including Korea [Bainbridge, 1986] and Morocco. In Morocco, the acorns of cork oak (Q. suber) are gathered in the fall for human consumption and sold in small baskets along roadsides [author’s observation].

The acorns of several species of Lithocarpus are also locally important food sources. The acorns of Lithocarpus edulis, a species indigenous to Japan, and of L. corneus, indigenous to southern China, are rather sweet and edible. [Harlow et al., 1979; Wickens, 1995]. In India, L. xylocarpus, a component of tropical semi-evergreen and Himalayan moist temperate forests, produces an edible nut that is eaten locally.^[38] The acorns of tanoak (L. densiflorus) were an important food item for several indigenous tribes in the northern Coast Range of California. In many indigenous communities, the main diet was salmon and tanoak acorns. Flour was made from the acorns that were ground and then washed in hot water to extract the tannins and bitter flavour. They acorns were cooked into a mush [Fowells, 1965; Peattie, 1953].

Table 8.1 Traditional and contemporary uses of acorns for human consumption

Sources: Peattie 1953, Little 1979, Miller 1997, Shiva, personal communication, Wickens 1995.

DYES

Fully ripe, crushed acorns of the North American oaks (Quercus alba, Q. rubra and Q. meuhlenbergii) are a dye source and produce a range of colours depending on the mordant used. A tan to medium brown colour is produced with chrome, dark brown with iron and golden brown with chrome and tin [Casselman, 1993].

FOOD FOR DOMESTIC ANIMALS AND WILDLIFE

Acorns have been a food for hogs since medieval times when they were turned loose in oak forests in England and other European countries to graze [Edlin, 1985]. Similarly in Portugal, the acorns of Quercus suber and other oaks have been used to fatten hogs. Hogs are allowed to range freely in oak forests toward the end of October and are collected in late January. They have been known to average a 30-kg increase in weight when fed on acorns.^[39]

The acorns of many species of oaks are an important wildlife food. Studies indicate that in Wisconsin the acorns of Q. bicolor were found to make up 27 percent of the diet of wild ducks. Other animals that feed on acorns include various songbirds, pigeons, quails, turkeys and rats, bears and deer [Burns and Honkala, 1990].

BEECH NUTS

The nuts of beeches (Fagus spp., family Fagaceae) are triangular in shape and usually occur in two within a bur covered with small spines (Figure 8.4). They mature in a single season.

Figure 8.4 Foliage and nuts of the European beech (Fagus sylvatica), Parco Nazionale Abruzzo, Abruzzo Region, Italy

HUMAN CONSUMPTION

The nuts of American beech (Fagus grandifolia) are sweet and have a protein content of about 20 percent [Thomas and Schumann, 1992). The nut can be readily opened with a thumbnail and is reported to be one of the sweetest, most delicious products of northern forests. Collection of beechnuts in northeastern forests was once a popular activity. They were collected in large numbers in the fall and sold commercially. Today beechnuts are rarely found in markets as a commercial product because of “modern sophistication” [Fernald et al., 1958]. A disadvantage of beechnuts as a food item for human consumption is that the fresh nuts spoil quickly. They can be dried in full sun for one to two days or roasted in a small oven to prolong storage [Thomas and Schumann, 1992].

BEECH NUT OIL

The nuts of European beech (F. sylvatica), on the other hand, have never been a popular food item for human consumption and were only eaten when driven by extreme hunger. An important use of beechnuts in Europe, however, was as a source of oil, especially in France. During the early 1800s, some beech forests produced as much as two million bushels of nuts that, when properly treated, yielded oil equal to 1/6 the bulk of the original nuts. Beechnut oil was said to be equal to olive oil in flavour [Fernald et al., 1958].

Production of beechnut oil involves grinding the nuts into a paste from which the oil is extracted. The oil ages well if stored in clay jars and buried in sand in a cellar. It will keep for up to ten years, and oil over six years is considered to be the best [Fernald et al., 1958].

Roasted beechnuts have also been used as a substitute for coffee in Europe [Ferruled et al., 1958].

FOOD FOR DOMESTIC ANIMALS AND WILDLIFE

The nuts of European beech (Fagus sylvatica) have been used to fatten hogs [Harlow and Harrar, 1950; Hora, 1981]. Beechnuts are also a valuable food for wildlife including squirrels, mice, pigeons, pheasants and jays [Edlin, 1985]. Nuts of American beech (F. grandifolia) were a favourite food of the now extinct North American passenger pigeon.

CHESTNUTS

Chestnut is a fast-growing, long-lived deciduous tree and its nuts represent one of the most important nut crops in the temperate zone. Chestnuts are also gathered in natural forests. Species of Castanea (family Fagaceae) are indigenous to all three continents of the Northern Hemisphere, and the chestnut has long been cultivated throughout China, Korea, Japan and the Mediterranean basin.

HISTORICAL ASPECTS^[40]

Chestnuts have been cultivated for at least 3000 years in the Mediterranean region. The ancient Greeks are thought to have been among the first to cultivate the nut (Chua and Klinac, 1992]. The Romans introduced this tree to Britain during their period of domination and colonization between AD 42 and 410 with the objective of raising the familiar nuts that were, in Italy, a staple food for their legionaries. However, the cooler climate of the British Isles was not conducive to good chestnut harvests [Edlin, 1985]. In Asia, the Japanese chestnut (C. crenata) has been cultivated since at least the eleventh century, and the Chinese chestnut (C. mollissima) possibly as long ago as 6000 years (Chua and Klinac, 1992].

IMPORTANT SPECIES^[41]

Species of Castanea that have either been or are currently important in commercial production include the American chestnut (C. dentata), the Chinese chestnut (C. mollisima), the Japanese chestnut C. crenata) and the European chestnut (C. sativa) [Wickens 1995].

Castanea dentata is native to the eastern United States and adjoining portions of Canada. This is the tallest member of the genus Castanea, capable of achieving heights of approximately 20-35 m (Harlow and Harrar, 1950] and has nuts that are sweeter than most other species. The burs usually contain three nuts each. American chestnut was also a prime timber producing species, however, this tree is no longer a viable source of nuts or other forest products because it has been decimated by an introduced fungus, Cryphonectria (Endothia) parasitica that causes chestnut blight (see textbox 8.2).

Castanea mollisima is native to China with a natural range that extends from south China to north of Beijing and is considered to be the hardiest of the Asian chestnuts. This tree is more resistant to the chestnut blight fungus than other species of Castanea. Its nuts are sweeter and finer textured than those of C. crenata, and it is currently the major commercial nut-producing species. Several horticultural varieties, with varying degrees of hardiness, have been developed. This tree does not have good form and is not important as a timber-producing species.

The Japanese species (C. crenata) is found in hilly and mountainous regions. It is not as tall as C. dentata, and its nuts are intermediate in size between those of C. dentata and C. sativa. The nuts are large and coarse-textured. They lack the flavour of other chestnut species.

The European or Spanish chestnut (Castanea sativa) is a tree that has a similar growth habit to that of C. dentata and can reach similar heights. This tree is found in southern Europe, North Africa and the Near East. In the eastern part of Peloponnese peninsula in southern Greece, there are about 1 000 ha of C. sativa groves. The trees grow naturally but are also cultivated in plantations [Moussouris and Regato, 1999]. In the mountainous regions of Italy, it forms pure or nearly pure stands at mid to high elevations [author’s observation]. This tree is somewhat less susceptible to chestnut blight than the American species but can suffer serious damage that has resulted in reduced nut yields [Wickens, 1995]. The nuts of C. sativa are about the same size as those of C. crenata but sweeter in flavour.

Other species of Castanea have smaller nuts and have been used locally as traditional sources of food while others are important as wildlife food. The nuts of the Chinese species C. henryi are small but have an excellent flavour. The “chinquapins” of eastern North America (C. ozarkensis and C. pumila) produce small, sweet nuts that have a good flavour but are difficult to shell. The nuts of these trees are used to fatten hogs [Wickens, 1995].

NUTRITIONAL VALUE

Chestnuts are both a tasty and healthy food and compare in nutritional value to wheat and brown rice. They are high in carbohydrates and have the lowest fat content of all major edible nuts (1-3% compared to 50% for some other nuts). Chestnuts contain quality protein and no cholesterol.^[42] The nutritional value of chestnuts varies by species and by the manner in which they are prepared [Wickens 1995] (Table 8.2).

PRODUCTION AND TRADE

Chua and Klinac (1992) discuss global commercial production and trade in chestnuts by major producing regions of the world in a paper (Table 8.3).

China

China is currently the world's largest producer and exporter of chestnuts. From southern to northern China, 300 different cultivars are grown under diverse and variable climatic conditions and environments, but only about 50 cultivars are produced commercially. Yields from Castanea mollissima average about 75 nuts/kg. There are some exceptionally large cultivars (40 nuts/kg) but these are not common. Average yield is ca 8 t/ha, with up to 15 t/ha possible from dense plantings (3 x 2 m) and high yielding cultivars (figure 8.5).

Figure 8.5 Burrs of the Chinese chestnut (Castanea mollisima) Henan Province, China.

China's statistics are not very reliable if local consumption is included. In 1991, national export figures were 58 000 t (fresh and processed), but local consumption is high. A conservative estimate of total production is 80 000-120 000 t. Another source estimates production at 100 000 t/a to 240 000 t/a.^[43] However, in a country of over one billion people, nobody seems to know for sure.

Castanea crenata is grown in Kirin Province with Japanese joint-venture interests. These nuts are cut by hand in a special way, leaving the raw flesh free of the inner skin (pellicle), a method that has been introduced by Japanese technicians sent to China. China has been chosen over Korea because labour is cheap (US$ 1.50 per day) and cutting is highly labour intensive. Hong Kong is the biggest importer of fresh and dried pellicle-free chestnuts, taking about half of China's export and then re-exporting to Southeast Asia. Most are consumed by overseas Chinese who eat them throughout the year, but more so around October, November, and December when fresh nuts are available for roasting. Chinese cuisine uses chestnuts in high-class dishes. The dragon-boat festival around May uses up most of the dried chestnut crop.

Table 8.2 Nutritional value of chestnuts¹

¹ Species not given
Source: USDA data presented by Great Lakes Chestnut Alliance^[44]

Table 8.3 Annual chestnut production by principal producer countries¹

¹ Data are for the period 1978 to 1991.
Source: Great Lakes Chestnut Alliance, Chua and Klinac 1992.

Korea

The world's second largest producer of chestnuts is Korea, with a production of up to 80 000 t/a, of which up to 30 000 t are exported to Japan. Most natural stands of chestnut were largely destroyed in the 1950s as a result of war and chestnut gall wasp epidemics. Since then, more than 200 000 ha of orchard have been established, mostly in the south and west, on poor soils. Yields of 2-10 t/ha are reported at 400 trees/ha with one-third of the trees used as pollination sources. Blocks of trees are planted in 25-year cycles, with peak production around year 15. Chestnuts are a major export earner for Korea (US$ 80 million/year compared to US$ 64 million for all other fruit exports combined) and much effort has been devoted to developing the early-harvest, dark, even-sized chestnuts preferred by the Japanese market.

However, since 1977 the rate of planting has dropped due to increasing labour costs (especially peeling) that in turn has led to increasing mechanization, where possible. Most production is by Castanea crenata x crenata (Japanese cultivar) crosses, grown on rootstocks.

Japan

Japan is one of the largest chestnut consuming countries in the world and the biggest chestnut importer. Japan has a long history of chestnut cultivation and the development of new, high-performance cultivars. In practice, however, they face severe production problems due to blight and especially to insect pests, such as the gall wasp that entered Japan in 1941. From 1959 to 1964, the area of chestnuts in production doubled, but because of the gall wasp production levels remained almost unchanged. In 1978, domestic production exceeded 60 000 t, with another 23 000 t being imported. Today’s Japanese market is basically segmented into several components. First is the current national production of C. crenata of 40 000 t/a. Japanese chestnut prices range from US$ 6.75 to US$ 8.50 per kilogram for ordinary cultivars. Through many years of habit and attachment to their winter festivals where food made of chestnut paste are widely eaten, Japanese prefer chestnuts as a winter food.

The second major source of chestnuts after Japan is China. Chinese chestnuts are imported during winter and well liked because their pellicle can be easily removed after roasting or boiling. The period of import supply is from October to December. They arrive in 60-kg jute bags. Total 1991 importation was approximately 28 000 t. Prices set by the Chinese National Export Corporation are about US$ 2.75/kg at the wholesale level.

Third in importance are supplies of chestnuts from Korea. Korean chestnuts are similar to Japanese cultivars, but Korea provides mainly hand-cut chestnuts. The cutting process is labour intensive, and great importance is attached to the manner of cutting. The product is priced as first or second quality according to the cut, and the Japanese have sent expert women cutters to Korea to train locals. A top cutter produces 10 kg/day of cut chestnuts. All pellicle and outer skin surface is removed, leaving only the white flesh. Large chestnuts are preferred but pricing is by weight. The annual supply for this type of cut chestnut is 15 000 t.

About 1 500 t of Italian chestnuts (Castanea sativa), without shell and pellicle, are also imported into Japan. These are used mainly for marrons glacés and also in paste form for confectionery. For marron Glico, the nut is stored for a period (chilled) that allows the shell and pellicle to be removed more easily from the nut by steam blasting. The nut is then re-frozen for export. For paste, the Japanese are very wary about the preservatives used. Italian-shelled chestnuts are shipped in 11-kg cartons.

Europe

Chestnut blight and phytophthora root rot have had a dramatic effect on chestnut production in Europe. From about the turn of the century, when chestnut blight was introduced, most of the traditional chestnut-producing areas of Europe have often shown a progressive decline in chestnut production. Both France and Italy suffered about an 85 percent decline between the turn of this century and 1965. This has been partly due to urbanization and population drift toward the cities; partly to increasing labour costs and the difficulties of mechanization in many production areas (trees are most often on steep slopes); but mostly due to the spread of the disease. Expensive and prolonged research efforts into breeding new, disease resistant cultivars, improved disease controls and the development of better rootstocks and cultivation methods have apparently helped stabilize this decline in recent years. High prices for processed, peeled and frozen chestnut products, especially in the United States where they sell for more than US$ 6.00/kg, have prompted moves to expand the chestnut industry in many countries.

An illustration of some of these changing trends can be seen in chestnut production in France. At the beginning of the century, France grew nearly 400 000 t of chestnuts. By the 1960s this had dropped to 45 000 t/a and to 27 000 t/a in the 1970s. By 1978, France was producing 20 000-25 000 t/a and importing about 10 000 t/a. Over the same time period, fresh consumption declined, while that of processed products increased proportionately. Within the European Community, France is now the biggest chestnut importer, mostly from Italy, but also from Spain and Portugal. In 1993 the value of Italian and Spanish chestnut production reached Lit 56 452 million (35 721 t) and Ptas 2 650 millions (52 300 t), respectively [Cesaro et al., unpublished].

Italy is currently the largest chestnut producer in Europe, at over 50 000 t/a. Italy is also the world leader in the production of marrons and processed chestnuts. Most exports go to France. Within Italy, the traditional use of dried chestnuts as flour in cooking is declining, but overseas the popularity of these and similar products is increasing, especially in the United States. As a result, production is being increased, with new orchards being established and research continuing on the development of new and improved cultivars. Extra income is generated in some chestnut orchards by the production of honey and/or the edible mycorrhizal fungus, Boletus edulis, which is sometimes worth more than the chestnut crop itself (see section on edible mushrooms in Chapter 9).

Spain is the next highest European producer after Italy and France. In 1986, 120 000 ha of chestnuts were being grown, mostly in northern and western Spain, producing more than 20 000 t. In addition to having a large local market, peeled nuts are exported to Italy and France.

Elsewhere in Europe, some chestnut production is reported from Turkey (52 000 t/a), Greece (18 000 t/a) and Croatia (70 000 t/a). In Switzerland, 44 000 ha have been planted with chestnuts, mostly south of the Alps. All Swiss production is consumed locally, with an additional US$ 10 million worth imported annually.

United States of America

In the United States, the first European settlers found extensive native forests of American chestnut (Castanea dentata). European chestnuts were introduced in the early 1700s, Japanese chestnuts by 1860, and Chinese chestnuts in the late 1800s. However, the introduced chestnut blight destroyed almost all natural C. dentata forests and most C. crenata and C. sativa plantings by the 1950s. Therefore, many present-generation Americans are unfamiliar with chestnuts.

Presently in the United States, there are an estimated 800 ha of nut-bearing chestnut plantings, and perhaps 2 000 ha of non-bearing trees. Most production is concentrated in the western states of California, Oregon and Washington. The objective of the United States chestnut industry is to increase plantings to 120 000 ha. This is the area that would be required to bring American consumption to the European levels. At present, the United States import US$ 20-40 million chestnuts annually, mostly from Italy.

Because chestnut blight killed off almost all native trees, extensive efforts are under way to re-establish the "natural" chestnut forests of the country. This is the main concern of many chestnut researchers and supporters, and emphasis is placed on forest- rather than orchard-related problems. Tree form and timber production often takes priority over nut production.

Nevertheless, an organized chestnut industry is developing. Plantings on the West Coast are mostly C. sativa x C. crenata. East of the Rocky Mountains, most growers plant the blight resistant Chinese chestnut or its hybrids. Production guidelines to growers are based on 1.8-3.6 trees/ha at maturity (12-15 years) and a return of around US$ 4.00/kg wholesale. In parts of the country, chestnut production is replacing the more traditional growing of hazelnuts.

Australia

Australian chestnut production is estimated at 538 t/a from approximately 250 growers. By 2001, production is expected to reach 3 600 t, all sold locally. Much Australian chestnut production is concentrated in the state of Victoria, where there are sometimes serious disease and storage problems, and many of the older, inferior chestnut selections are now being replaced with newer material.

CULTIVATION

Most commercial production of chestnuts is in orchards although some are still gathered in the wild (Figure 8.6). They have traditionally been grown on hilly land that is unsuitable for other agricultural crops. The preference of chestnuts for lighter soil provides an opportunity to utilize land that is marginally productive. Chestnuts prefer a well-drained, slight acidic (pH 5.0-6.9) soil and tend to thrive in sandy soils. Chestnut trees on heavier (clay) soils have been noted to perform in outstanding fashion if the drainage patterns prevent standing water or soil saturation for extended periods. Chestnut trees do not like "wet feet" and should not be planted in flood plains. Established trees are quite drought tolerant.

Figure 8.6 A Castanea sativa orchard, Lago di Vico, Lazio Region, Italy.

The nutrient requirements of chestnuts are similar to those of other tree crops. They respond to an early spring application of nitrogen with accelerated growth. In bearing years, nitrogen helps ensure larger nuts. For other nutrients, a soil test is recommended so that any deficiencies can be identified. Some producers recommend applying boron to ensure nut set. Most soil types have proven sufficient to some level of chestnut production. The Koreans and Chinese have discovered that a dormant application of phosphate (late November to early April) increases the ratio of female-to-male blossoms, perhaps accounting in part for the rather stunning production figures reported from Asia (9 to 11.2 t/ha).^[45]

HARVESTING AND STORAGE

Chestnuts are hand harvested in the major production areas of Europe and Asia with methods little changed over the past 2000 years. However, high labour costs in regions such as Europe and North America and changing cost structure in agriculture may dictate the need for mechanically assisted harvesting options such as mechanical tree shakers. Fortunately, new orchards can be planned and managed to maximize the benefits of mechanized harvesting.

The simplest harvesting method is to let the nuts fall to the ground naturally, then pick them up by hand or gather them on tarps. New, low-cost polypropylene net tarps have helped reduce harvesting costs for other orchard crops. The use of tarps to catch naturally falling nuts, however, is limited to small orchards of 4 ha or less. As the size of the chestnut orchard increases, the harvest becomes more difficult to manage. A large orchard of seedling trees would have a natural nut drop period of 10-15 days most years but may range up to 30 days in some years, depending on environmental conditions. During extended harvest periods, the nuts are subject to fungal infection if stored improperly. Fallen nuts have to be picked up at least every few days.

Chestnuts add half of their final weight during the last two weeks on the tree. To maximize the orchard yield and nut quality, a mechanical harvest (shaking) must be accomplished after the nuts reach maturity and before natural nut fall begins.^[46]

Harvested nuts may be held in refrigerated storage at 0-1^oC in well-ventilated polyethylene liners up to several months. Damage by weevils (Coleoptera: Curculionidae) may occur during storage. However, it is not possible to remove infested nuts by flotation prior to storage. The risk of low-level fungal infection increases if visible moulds are absent or at low levels and are not detected. Fresh nuts can dry out and harden if not stored properly and cannot be roasted unless regenerated by soaking [Wickens, 1995].

PREPARATION AND USE

Chestnuts are starchy and a short curing period of three to four days is required to allow some of the starch to convert to sugar. This is especially true if the nuts have been refrigerated. Eating quality is best during harvest time. In Europe it is traditional for street vendors to roast chestnuts over charcoal fires and sell them in small quantities (Figure 8.7). Shelled nuts can be ground into flour and eaten as a bread or porridge. They can be roasted or boiled and eaten as a vegetable or used as poultry dressing. In France, a traditional way to serve chestnuts is to preserve them in syrup as marrons glacés or other sweets [Wickens, 1995]. Before cooking, an “x” should be cut into the flat side of the chestnut with a small knife in order to avoid bursting the shell during cooking.

Figure 8.7 A street vendor selling fresh roasted chestnuts, Piazza di Spagna, Rome, Italy.

NUTS OF CASTANOPSIS AND CHRYSOLEPIS

The genera Castanopsis and Chrysolepis are closely related members of the family Fagaceae. Some authorities list them under a single genus (Castanopsis). The primary difference between the two genera is that the nuts of Castanopsis require one year to mature and the inflorescence spikes are unisexual whereas the nuts of Chrysolepis require two years to mature and the sexes are mixed on a single inflorescence spike [Hora, 1981].

Trees and shrubs of the genus Castanopsis (Fagaceae) are widely distributed throughout the tropical and temperate forests of Asia. Many species produce nuts that can be are eaten raw, roasted or boiled. Several temperate forest species are used in confectionery [Wickens, 1995] (Table 8.5).

The nuts of the North American Chrysolepis (Castanopsis) chrysophylla are sweet and have been used as a food source by indigenous tribes [Wickens, 1998]. However, crops are not sufficiently reliable for a staple food source. Moreover, they are difficult to extract from their spiny hulls [Peattie, 1953]. The nuts of C. sempervirens, another North American species, were also used as a food source by indigenous tribes and are reported to be good tasting when roasted and served with butter and salt [Wickens, 1995].

Table 8.4 Edible nuts from temperate forest species of Castanopsis spp.

Sources: Hora, 1981; Wickens, 1985; Shiva - Personal communication.

HAZELNUTS

Hazelnuts, also known as filberts or cob, are the nuts of various species of Corylus (family Betulaceae). They have a pleasant flavour, and dry nuts contain about 16.3 percent protein, 61.2 percent fat and 11.5 percent carbohydrates. The nuts are sold in shell to consumers or shelled for use in various food products, especially for nut chocolate. The nut kernels may be ground into flour and baked as filbert bread. In addition to being edible, hazelnuts are the source of both edible and industrial grade oils. Two species, the European hazel (C. avellana) and, to a lesser extent, the Turkish filbert (C. maxima) are grown in orchards and are an important agricultural crop in several countries with 70 percent of world production coming from the Black Sea area of Turkey. World hazelnut production has almost doubled from 1980 (421 136 t) to 1998 (771 827 t). Other areas of production include the coastal regions of Italy (20%), the Mediterranean coast of Spain (7%) and western Oregon and Washington (3%) [Wickens, 1995). Greece, France and Portugal are countries with small shares of world hazelnut production. Germany has been the main hazelnut importer reaching 43 percent of world imports in 1997. More than half of the world hazelnut export goes to European countries [Sengül and Sengül, 1999].

In some areas of Eastern Europe and the Near East, hazelnuts are still gathered from wild trees that grow in the forest. In Lithuania, they are gathered by families to satisfy household needs in conjunction with edible forest mushrooms and various berries [Rutkausas, 1998]. In Belarus, 24 t of hazelnuts were harvested in forests during 1996 and there is an estimated potential crop of 809 t annually [Ollikainen, 1998]. Hazelnuts are also collected on a small scale in Armenia [Ter-Ghazaryan and Ter-Ghazaryan, 1998].

HICKORY NUTS

Trees of the genus Carya (family Juglandaceae), commonly known as hickories, are found in North America and Asia. It is a fast-growing deciduous tree; several species produce edible nuts, and the nut kernels of at least one species are the source of edible oil.

Pecans, produced by Carya illinoensis, a tree native to the southeastern United States, Mexico and parts of South America, are an important agricultural crop. The nut meats are widely used in confectioneries and desserts. The wild trees produce edible fatty nuts (dry druoes), which Indian tribes in these areas eat.^[47] The nuts of the North American shagbark hickory (C. ovata) and of the shellbark hickory (C. laciniosa) were important food sources for the indigenous tribes and are still collected and marketed on a small scale in some parts of the eastern United States. Other North American species of Carya that produce edible nuts and have been used as food for human consumption include C. aquatica, C. carolinae-septenrionalis, C. cordiformis, C. glabra, C, myristiciformis, C. ovalis, C. pallida, C. texana and C. tomentosa. The nuts of several of these species are astringent, bitter tasting, have small nuts or shells that are difficult to crack (Thomas and Schumann, 1992; Wickens, 1995].

Asian species of Carya that produce edible nuts include Carya cathayensis of eastern China and C. tonkinensis of southern China, northeastern India and Viet Nam, the nuts of which produce an edible oil that is also used in lanterns [Wickens, 1995].

Hickory nuts should be gathered as soon as they fall from the trees, hulled and placed on screens to dry. When the kernels are crisp, they should be stored in mesh bags in a cool, airy location [Thomas and Schumann, 1992].

PISTACHIOS

The genus Pistacia (family Anacardiaceae) consists of about 10 species that are indigenous to Eurasia, North America and the Canary Islands and have edible nuts. Pistacia vera is cultivated as an agricultural crop in Mediterranean Europe, the Near East and California.

World production of pistachios is increasing. During the period 1979-1981, world production averaged 109 000 t/a and in 1993 it increased to 354 000 t. Major producing and exporting countries are Iran, Turkey, Syria and the United States. These four countries produce 90 percent of pistachio world production. Other countries that export pistachios include Afghanistan, Greece, India, Italy, Pakistan and Tunisia. Countries such as Germany, Belgium, Luxembourg and the United Kingdom import pistachio nuts in order to re-export them to other countries [Wickens, 1995; Sengül and Sengül, 1999].

In some regions of the Near East, pistachios are still gathered from wild trees. For example, in Balochistan Province, Pakistan, pistachios are gathered from natural forests of Pistacia kinjac by local tribes for their own consumption or sold in marketplaces [author’s observation].

The nuts of P. terebinthus, native to the Mediterranean region; P. texana, native to New Mexico and Texas; and P. mexicanus, native to Mexico and Guatemala, also produce edible nuts but are not grown commercially [Little, 1979; Wickens, 1995]. The fruit husks of Pistacia vera are used as a mordant and tannin source [Wickens, 1995]. Pistacia atlantica is native to, and common in, Algeria where its nuts are called elkhordiri. These nuts contain energetic oil, which is usually mixed with dates and can be eaten all day along with milk [Belhadj, 1999].

WALNUTS

HUMAN CONSUMPTION

The nuts of most species of Juglans (family Juglandaceae), a genus of trees indigenous to Asia, Near East, North and South America, are edible. The English or Persian walnut (Juglans regia) produces a large, sweet, meaty nut that is being cultivated and is an important agricultural commodity in parts of Europe and North America, especially California. This tree still occurs in natural forests of Turkey, Iran, Afghanistan, Central Asia and in the Himalayan range up to Bhutan, where nuts are gathered from this tree. In the Central Asian Republic of Krygyzstan, for example, natural forests of J. regia are found on the southern slopes of the western Tyan Shan Mountains. These forests are state-owned but the rights to harvesting walnuts are leased to private individuals under a concept of collaborative forest management. In exchange for the harvesting rights, individuals agree to manage and protect the forest (Haldimann et al 2000).

The nuts of North American black walnut (Juglans nigra) and the California walnuts (J. californica and J. hindsii) have a flavour that is stronger and richer than that of the English walnut. This property makes it the nut of choice for baking candy and ice cream products. The nut kernels are high in fats, protein and carbohydrates and compare favourably with meat in the amount of vitamins A and B and riboflavin. These trees are not normally grown in orchards for their nuts [Thomas and Schumann, 1992].

Butternut (J. cinerea), also indigenous to eastern North America, is a slow-growing, deciduous tree that grows best in moist soil but does tolerate dry, alkaline soil. It is similar to black walnut (Juglans nigra) and is also called white walnut or oilnut. The tree produces a thin, fragrant, oily kernel that can become rancid quickly and must be shelled and used soon after having been dried. The nuts serve as food both for people and animals (e.g. squirrels and other rodents). They are sweet and good tasting when eaten straight from the shell or can be roasted or baked in cakes and pastries [Thomas and Schumann, 1992]. They are especially popular in New England for making maple-butternut candy. The nuts occur singly or in clusters of two to five and remain usually on the tree until after leaf fall.

Other temperate species of Juglans that have edible nuts and are at least locally important food sources include J. ailanthifolia of China and Japan, J. australia of Argentina and southern Bolivia, J. boliviana of Bolivia and Peru, J. cathayensis of central China, J. duclouxiana of the mountainous regions of Asia, J. kamaonia, of the western Himalayas, J. major of the southwestern United States and adjoining parts of Mexico, J. mandchuriana of northern China, J. microcarpa of western North America and J. subtropica of the Andean Cordillera. The nuts of several species of walnuts are used for extraction of cooking oil [Wickens, 1995].

DYE

The hulls of the nuts of Juglans regia, J. nigra, J. cinerea and other walnuts provide fast brown dyes that can be used to dye both plant and animal fibres. The Ancient Romans introduced J. regia to Europe both for its value as a food item and as a dyestuff. The early American colonists soon realized the value of both J. nigra and J. cinerea as a dye source. The hulls of J. nigra yield the most pigment and provide the darkest colours. Hulls of J. cinerea were used to dye the uniforms of Confederate soldiers during the American Civil War [Buchanan, 1987].

In the altiplano of northern Ecuador, weaving is an important local enterprise. Almost every home has at least one loom and production of hand-woven tapestries, table linens and related items are an important/art of the local economy. Most colours are now obtained from chemical dyes. Two natural dyes still remain in the repertoire of the altiplano weavers, however; indigo, an important blue dye source, and walnut hulls, collected from Juglans neotropica, an indigenous tree. Weavers are able to obtain a range of colours from deep chocolate brown to beige from the hulls of these nuts that are used to make intricate designs in tapestries [author's observation] (Figures 8.8 and 8.9).

Figure 8.8 Juglans neotropica growing near Otovalo, on the Ecuadorean altiplano. The nut hulls of this tree are an important local dye source.

Figure 8.9 Wool is dyed rich brown colour in a dyebath made from the nut hulls of Juglans subtropica, Otovalo, Ecuador.

The hulls of all walnut species can be dried for storage or used fresh. A few dozen nuts will dye several hundred grams of fibre. The hulls can be soaked overnight and simmered or boiled for more intense colours. However, this process gives off strong odours [Buchanan, 1987].

OTHER PRODUCTS

The processed shells of J. nigra are used for a variety of industrial products including:

· Metal cleaning and polishing - A soft grit abrasive made from processed walnut shells is used for cleaning jet engines, electronic circuit boards, ships and automobile gear systems. This product is also well suited for air-blasting operations, deburring, descaling and polishing operations because of its elasticity and resilience. The shell is non-toxic and dust free and can be used on plastic, aluminium and soft alloys because it produces a smooth surface without scarring.

· Oil well drilling - Black walnut shell is widely used in oil well drilling and in making and maintaining seals in fracture zones and unconsolidated formations.

· Paints - The paint industry uses the shells for plaster-effect paint. Paints and varnishes mixed with walnut shells are far superior to ordinary sand paint

· Explosives - Black walnut shell is used by manufacturers of explosives as filler in dynamite. It is compatible with other materials and works well for this use.

· Cosmetic cleaners - Black and English walnut shell is ideal as the gritty, rough agent in soaps, cosmetics and dental cleansers [Thomas and Schumann, 1992].

HARVESTING AND PROCESSING

Unlike the English walnut, which is grown in orchards, black walnuts are collected from wild or roadside trees and forest plantations grown for high-quality walnut logs. In the mid-western United States, Juglans nigra is often grown as a forest plantation species by small private landowners and the nuts can provide an additional source of income. This tree is sometimes grown as an agroforestry species in conjunction with wheat, milo, soybeans or fescue. In California, J. californica is a commonly planted roadside species where nuts can be readily gathered [Thomas and Schumann, 1992].

The walnut husk must be removed before decomposition begins to saturate the shell, giving the nut meat a bitter flavour. In the absence of processing machinery, this is a messy and cumbersome project. One way is to place the nuts on a hard surface and either step on them or run an automobile over the nuts. Washing in a garbage container several times can then clean the nuts. The hulled nuts are dried in shallow layers for several weeks and stored in their shells in mesh bags in a cool location [Thomas and Schumann, 1992].

There are two plants in the United States that commercially shell black walnuts. These are located in Lodi, California, and Stockton, Missouri. The plants purchase walnuts from farmers of the area. These plants market the nut meats that retail for up to approximately US$ 6.50/kg, nearly twice that of commercially grown English walnuts. They also market the shells, which sell for US$ 60-90/t [Thomas and Schumann, 1992].

PRODUCTION AND TRADE

World walnut production increased by 37 percent from 1980 to 1998 when it reached the quantity of 1 095 041 t. China (22.9%), United States (18.7%), Turkey and Iran are the main producers. United States are the largest exporter (shelled walnuts), accounting for around 50 percent of total world exports, followed by China and France. The main importers are United Kingdom, France and Germany [Sengül and Sengül, 1999].

ALMONDS

As for walnuts, almonds are regarded as an agricultural crop and will not be discussed in detail in this document.

World almond production has increased by 45.1 percent from 1980 (919 620 t) to 1998 (1 334 442 t). United States (30%), Spain (15-25%) and Italy are the main producers. Other producing countries are Iran, Morocco, Greece, Syria, Tunisia, Pakistan and Turkey. World shelled almond export doubled during the period 1980-1997, from 105 616 t to 216 286 t.

The United States is the largest exporter and accounted for 70.3 percent in 1997, whereas Spain is the largest exporter among the Mediterranean countries. The main importer is the European Union with more than 50 percent of total world almond imports. Germany accounted for 27 percent of world imports, followed by France and Japan [Sengül and Sengül, 1999].

MINOR NUTS

The fruit of the Southern Hemisphere temperate broad-leaved trees of the genus Nothofagus are one-seeded nuts [Hora, 1981]. The nut of N. alpina (= procera) (common name rauli), indigenous to Argentina and Chile, are reportedly edible [Wickens, 1995]. The nuts of N. glauca (common name hualo), also indigenous to Argentina and Chile, are more than 1 cm long, one of the largest nuts of the genus Nothofagus [Donoso Zegers, 1983]. These nuts were used as food by indigenous tribes that inhabited the area.^[48]

Several species of Pterocarya, a genus of Asian trees closely related to Carya and Juglans (family Juglandaceae), produce edible nuts that are locally important. Known as wing nuts, they include P. franxinofolia, indigenous to the Caucasus; P. rhoifolia, of Japan; and P. stenoptera, of China [Wickens, 1995]. The wing nut is approximately 3/4" in diameter and grows suspended in long, stringed spikes from the tree. The nuts are ripe in autumn when they turn tan in colour.^[49]

The nuts of yellow buckeye (Aesculus octandra), as well as of other species of this genus, contain much starch but are not suitable for food because they contain a poisonous glucoside called aesculin. However, several indigenous American tribes roasted the nuts among hot stones, thus loosening the shells. The nuts were then peeled, mashed and leached with water for several days. This apparently removed the aesculin and resulted in a highly nutritious food. The seeds of both A. octandra and A. glabra are poisonous to livestock [Fowells, 1965].

Figure 8.10a Nuts of: Fagus sylvatica.

Figure 8.10b Nuts of:Corylus avellana.

Figure 8.10c Nuts of:Carya spp. (hickory).

Figure 8.10d Nuts of:Pterocarya spp.

Figure 8.10e Nuts of:Aesculus spp.

Figure 8.10f Nuts of:Castanopsis spp.