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Tree nuts are a nutritious and versatile category of foods and food ingredients. Most are eaten directly or mixed with other nuts and peanuts, but they also are converted into specialty oils, butters, granules, and components of foods such as ice cream and confections.
The significant tree nuts are almonds, Brazil nuts, cashews, hazel nuts, macadamias, pecans, pine nuts, pistachios, and walnuts. Some are native to the Americas, while others originated in Australia and Africa. The international trade in tree nuts is complex and often entangled with politics and economic policies.
Pat Kearny (phone 703-841-1600), principal of PMK Associates in suburban Washington, D.C., wrote an extensive article on nuts in the Wiley Encyclopedia of Food Science and Technology, 2nd ed. A nutritionist with a focus on strategic marketing and communication, she led the effort that established the Tree Nut Council and Peanut Institute. She said that between 1989 and 1995, the snack nut market declined by about 40% as a result of public concern about fat consumption. Thanks to wide dissemination of scientific research on nuts in the diet by these organizations, the perception that nuts are “bad food” has been reversed and a substantial portion of the market regained.
Not only do nuts contain unsaturated fats, but they also are sources of vital minerals and phytochemicals. People who consume nuts regularly seem to observe weight-loss diets better and experience other benefits, Kearny said.
Peanuts, actually a legume, are the most popular nuts, and about 50% of the peanuts grown are used to make peanut butter. The balance are eaten as salted snacks, shelled or in shell, and in confections. Tree nuts are most often consumed in snacks and confections.
Tree Nut Sources and Uses
Tree nuts are grown in various locations around the world and are used in a variety of forms and applications.
• Almonds, along with walnuts, are the most popular tree nuts. Almonds are grown in central California and around the Mediterranean. Almond products include in-shell, shelled, shelled and peeled (blanched), slivered, chopped, flour, roasted, sweetened, and salted. They are found in marzipan and candy bars, as sugar-coated snacks, and as a cosmetic base. Harvest in California is mechanized, using tree shakers to knock the nuts to the ground, where they dry in the heat and are then collected and taken to central grading and processing.
Like almost all tree nuts, almonds have a hard brittle shell which is removed by careful crushing. Electronic sorters are used to remove foreign matter, bits of shell and defective kernels.
• Brazil Nuts are grown in the Amazon basin and are collected from the wild. They are eaten raw, roasted, and salted. Brazil nuts are involved in an interesting program to promote sustainable and environmentally sound communities in the area. The protein morikue, a by-product of Brazil nut oil processing, has value in hair-care products. Aveda, in cooperation with Conservation International, is supporting training and establishment of new businesses in Peru to establish a supply of this ingredient while improving the economy of the rural people.
• Cashews are one of the more valuable tree nuts and also one of the more exotic. They probably originated in Brazil and were spread by the Portuguese to Africa and India. Now they are grown in Sri Lanka, India, Tanzania, Mozambique, Brazil, and Venezuela. Only about 10 lb of nut meat are produced by a tree in a year. The nut grows at the end of a pear-like fruit, called the cashew apple, which can be used to produce juice, jams, and preserves but often is wasted. The nut is surrounded by a hard shell and a corrosive liquid which has value as a chemical source for use as a lubricant and other purposes. Traditionally, nuts were cracked by hand, the juice collected, and the nuts cleaned and dried. They are still processed this way in some places. In others, there is some automation.
In Tanzania and Mozambique, investments were made to do more processing in the country of origin, but the plants have not been operated. As a result, many nuts are exported raw, at much lower value, especially to India, where they are used when that country’s own supply is short. Cashews represent an opportunity for creative process development and improvement in the developing countries where they are grown.
• Hazelnuts are an ancient agricultural crop, probably originating in Asia, but now grown in Oregon as well as Turkey, Spain, and Italy. They are also known as filberts from the fact that August 20, when they are supposed to start ripening, is Saint Philibert’s Day. Hazelnuts are popular in European chocolates and other foods. Floyd Aylor (503-538-2156), President of Columbia Empire Farm in the Willamette Valley south of Portland, Ore.—one of the larger growers of nuts and berries in the country—described his operation and how hazelnuts are vertically integrated from planting through to retail operations in the Northwest. The processing plant is in the middle of an orchard and makes several hazelnut candies (clusters covered in chocolate, brittle, and caramel), as well as preserves from a variety of berries (raspberries, lingonberries, huckleberries, and strawberries). The company sells some nuts in bulk but tries to sell most through its retail operation, Your Northwest, and specialty stores. About 5% of sales are over the Internet.
• Macadamias originated in Australia and are the only commercial agricultural crop to do so. Hawaii is now the major producer, but small quantities are also grown in California. Macadamias are primarily valued as a high-quality, gourmet snack, much of which is sold to tourists. South Kona Macadamia Nut Co. on the Big Island, Hawaii (www.southkonamacs.com), has developed patented processing technology which sonically cracks the hard shell without requiring drying first. This is said to produce better-quality nut meats.
• Pecans are the only tree nut native to North America and are one of the most valuable nut varieties now grown there. According to Kearny’s article, pecan shelling plants have capacities of 1–30 tons/day, and some operate year round, relying on cold storage of the fall harvest. The nut is grown in the southeast, so that is where the processing plants are. Shelling is automated and requires softening of the nut to avoid shattering of the nut meat. Softening is achieved by soaking in chlorinated water or by applying steam, although the steam can discolor the meat. Meat and shells are separated on screens, and the meats are dried before storage and packaging.
• Pine Nuts, or pignoli, are usually associated with ethnic foods, such as Italian, Greek, and Spanish cooking. They are gathered from pine trees around the Mediterranean and are dried for sale. They are used in pesto, added to salads, and sometimes cooked in bread.
• Pistachios are a very old edible nut, probably originating in the Middle East. They are grown in California, Iran, and Turkey. Pistachios are the only nut that requires no further processing, as they dry naturally and crack themselves. In some operations, they are dried and sorted to eliminate empty shells. They are usually eaten as a snack but are also used in ice cream and candies. According to R.A. Stephenson, in his article on nuts in the Encyclopaedia of Food Science, Food Technology and Nutrition (Academic Press), pistachios provide 9% of United States nut consumption.
• Walnuts. English walnuts, black walnuts, and butternuts or white walnuts are the popular edible varieties and are grown all over the world. In the U.S., the major growing area is California. Walnuts are marketed shelled and unshelled and are consumed in snacks, cookies, and other foods. They are a popular culinary ingredient in salads and other dishes.
Common Processing Steps
Most tree nuts undergo similar processing steps: often drying to prepare for cracking, size separation, cracking, air aspiration to separate shell fragments, color sorting to remove other defects, and a final hand sort and inspection before packaging. As mentioned above, some nuts are moistened to prevent fracture of the nut meat and then dried later. For almonds and some other nuts, there may be a deliberate size reduction to produce slivers or other particles.
The highest value is normally the snack market, but the ingredient market also calls for high quality and consistency. Many nuts produce a distinctive edible oil, but because the fatty acids are highly unsaturated, the oils can oxidize quickly. They should be refrigerated and used quickly.
Nut shells are a common by-product with few uses. Some are used for cleaning hard surfaces where sand would not be acceptable, such as in food plants. Others are made into charcoal and many are burned for fuel.
Nut butters are typically made by fine grinding, often in two stages, of roasted and cooled nut meats. If they have a skin, this is first removed in a process called blanching, which normally is accomplished by rubbing between soft rollers. Since the grinding process creates heat, the butter should be quickly cooled to below about 120ºF. For crunchy butters, nut fragments can be added. Salt, sugar, and stabilizers may be added if desired.
Nut snacks are made by oil cooking, dry roasting, or just drying. The meats may be salted, dusted with other flavors, coated with sugar or other confections, or left plain. Sometimes makers of candies, cookies, and cakes process their own nuts to ensure the quality and condition they need.
In the Dordogne region of France, aperitifs and liquors are made from walnuts, chestnuts, and hazelnuts by extracting flavors from the nuts using strong brandy and then adding syrups and or wines. The oils of these nuts are also valued for salads and cooking. These products are not currently made in the U.S. but might be worth considering.
Tree nuts are interesting for the variety they offer in a diet, as good sources of nutrients, for their importance to many economies, and for the variety of challenges they offer in processing and application.
PRODUCTS & LITERATURE
• Ripening Enhancer, lysophosphatidylethanolanine (LPE), has received Environmental Protection Agency approval for use as a natural ripening enhancer and shelf-life extender for table grapes, cranberries, tomatoes, strawberries, blueberries, apples, and cut flowers. For more information, contact Nutra-Park Inc., 8383 Greenway Blvd., Suite 520, Middleton, WI 53562 (phone 608-662-9080, fax 608-662-8259, www.nutrapark.com).
• Continuous Steam Sterilizing System provides high-temperature, short-time decontamination of spices, herbs, seeds, rice, and grains. Self-cleaning rotary pressure valves feed product into continuous autoclaves, where it is exposed to saturated steam at relatively high pressure. A self-cleaning shaking-bed conveyor in the autoclave transports the product for the precise length of time needed for “kills” to occur. The product is then discharged through a rotary pressure valve and transported down a chute to a fluid-bed dryer/cooler. For more information, contact Ventilex USA, P.O. Box 717, Mason, OH 45040-0717 (phone 866-265-6823 or 513-398 8778, fax 513-398 7780.
by J. PETER CLARK
Consultant to the Process Industries
Oak Park, Ill.