In the world of nuts and berries, macadamia nuts are almost as precious as gold. These delicious, exotic nuts with their rich flavor and oil are considered delicacies and are served as dessert nuts. They are popular gifts at holiday times, both alone and when covered with chocolate. They are prized as souvenirs from Hawaii, and, thanks to Mrs. Fields' cookies, macadamia and chocolate chip cookies have brightened many afternoons at the local mall.
Macadamia nuts are associated in the minds of most Americans with Hawaii. Macadamias are a commercial crop in Hawaii, but they originated in northeastern Australia in the rain forests along the coast. The tree is from the family Protaceae and is one of about 10 species of which two grow best as commercially productive plants. The Macadamia integrefolia produces nuts with smooth shells, and the Macadamia tetraphylla has rough-shelled nuts.
Macadamia trees produce throughout their lives but they are slow growing. The demand for the rich nuts has outstripped growers' ability to produce them. Consequently, growers in many other countries including New Zealand, Zimbabwe, Malawi, South Africa, Kenya, Israel, Guatemala, Brazil, Mexico, and Costa Rica have begun planting large orchards. In the United States, California and Florida boast macadamia crops, along with Hawaii.
The macadamia nut was discovered by British colonists in Queensland, Australia, in 1857. Walter Hill, who was the Director of the Botany Garden in Brisbane, found one of the nuts, cracked it open using a vise, and planted the seed. This "first" macadamia nut tree is still growing and producing nuts, although typically the trees only produce for about 70 years.
Hill had been traveling on a botanical expedition with Baron Ferdinand von Mueller, who is considered the father of Australian botany and who held the post of Royal Botanist in Melbourne at the time. He is credited with naming the tree after Scotsman John Macadam, a friend, physician, and member of the Philosophical Institute of Victoria. Mr. Macadam never tasted the nut that bears his name after a shipboard injury caused his premature death en route to New Zealand.
Of course, the trees had long been known to the native Australian aborigines who called the macadamia trees kindal kindal and who feasted on the nuts in winter. The colonists took the tree to their hearts and began to learn to propagate it. The first known macadamia orchard consisted of 250 trees planted in 1890 on the Frederickson Estate in New South Wales, Australia. The tree was heavily cultivated and hybrids were grown from seeds and, more often, by grafting. Australia remains one of the world's major producers.
The macadamia migrated to Hawaii courtesy of William Herbert Purvis who gathered macadamia nuts near Mount Bauple in Queensland, Australia, and brought them to Hawaii's Big Island in 1882. He nurtured the imported nuts and planted them as seedlings in Kukuihaele, Hawaii. One of Purvis's original seedlings is also still growing and producing nuts.
Today, Mauna Loa Macadamia Nut Corporation is the largest manufacturer of macadamia nuts in the world. The firm's plantation was founded in 1948, the trees began to bear fruit in 1954, and the first commercial crop was harvested and processed in 1956. Over 10,000 acres of rich, volcanic soil host Mauna Loa's orchards. The single largest planting is not in Hawaii but on 3,700 acres in South Africa. The hybrid grown in New Zealand produces the most expensive macadamia nuts in the world; the Beaumont sp. does not drop its macadamias, so they are expensive to harvest and are also among the finest in flavor.
The raw materials needed for commercial production of macadamia nuts are the nuts themselves, as well as salt and oil.
Macadamia nuts are sold in jars and cans for home consumption. These nuts have been roasted in oil in the factory and salted. Unsalted nuts are also packed for commercial use, primarily by bakeries. The flavor of the nuts is well suited for use in many kinds of desserts. Design can become elaborate if the nuts are used in candies, cookies, and other products. A wide variety of desserts, souvenirs of the islands, and other treats containing macadamias are available on the market; some are byproducts of the macadamia nut processors, but, more often, other firms use the nuts as ingredients in their own product lines.
- 1 Macadamia trees require rich soil, about 50 in (130 cm) of rain per year, and temperatures that are not only frost-free but that vary within a limited range. The soil must also drain well, so not all tropical zones are suited to macadamias as a crop. The trees are evergreen and everbearing; they have leathery leaves much like holly that are shiny and 7-12 in (20-30 cm) long. The trees themselves grow to as much as 60 ft (18.3 m) high. They produce clusters of flowers that are white or pink and fragrant; about 300-600 flowers appear in sprays. Each flower spray produces up to 20 nuts, which have green, fibrous husks and hard, outer shells called pericarps. The pericarps split as the nuts ripen on the trees. Each nut (including the kernel in its shell) is approximately 1 in (2.5 cm) in diameter.
- 2 The flowering of the trees occurs over a four to six month period. Consequently, the nuts mature at different times over the course of the year. They are also biennial, so alternate years produce light then heavy crops from a single tree. The trees require pollination during flowering, so beehives are usually imported into the orchards. Weeds grow heavily among the trees, and insects proliferate in the tropical climate; mowing and bug control are required. The trees are also fertilized with husks from their own nuts, chicken waste, and carefully selected and controlled chemicals. When the nuts are ready to be picked, the trees are pruned first so the nut clusters are easier to reach.
- 3 Ripened and unripened nuts look identical, so producers either wait until the nuts fall to the ground or they harvest infrequently, approximately five or six times a year. The nuts are harvested through a complicated process that includes gathering by hand, shaking the trees and picking the fallen nuts, or picking them with a mechanical picker. Blowers are sometimes used to blow the nuts and fallen leaves into windrows so they can be collected by machine.
In the factory
- 4 The harvested macadamias are fed into large hoppers and then into a dehusker made of double rollers that strip the husk away. The husked nut has a moisture content of about 25%, and it has to be dried and cured to reduce its moisture content to about 1.5%. Drying is done in a greenhouse, and curing is accomplished by heating the nuts to 104-122° F (40-50° C). Some processors store the nuts in netted bags or onion bags during drying so the heated air can move freely through the nuts.
The lower moisture helps later in processing in separating the kernel from the shell. Macadamia nuts have the hardest shells to crack (although they are followed closely by the Brazil nut). The process of cracking the nuts also makes them rare and expensive. The hulls are too hard and smooth to be cracked by standard nutcrackers, rocks, or hammers. (In Hawaii, those who can collect the nuts from trees in their own neighborhoods often resort to driving cars over them.) In the factory, harvesting is complicated by the ever-bearing nature of the trees. Their nuts mature throughout the year (i.e., not seasonally), so the process of gathering and hulling the nuts is continuous and expensive.
- 5 To shell the nuts, they are passed through steel rollers that counter-rotate (rotate in opposing directions) and are carefully spaced and engineered to conform to the size of the macadamias. These rollers exert a pressure of 300 lb per sq in (21 kg per sq cm) on the shells and cause them to crack without damaging the kernels inside. An alternative process uses a cracking machine equipped with rotating knives that pin the nuts against a wedge shape and crack them. The kernels are passed through a series of blowers and trommels or gravity separators with holes that remove dust, dirt, any remaining bits of husk, or nuts that are substandard. Uncracked nuts are collected after they pass through the trommel and are recycled through the crackers. The air blowers separate the kernels from pieces of shell.
- 6 Optical devices inspect the nuts and sort them by color. Quality control inspectors also observe the passing flow of kernels and sort them by hand. Light-colored nuts are classified as Grade I or fancy nuts, and the darker-colored nuts or those that are not within a standard size range are sorted as Grade II. Grade I nuts are used for retail sales, while the Grade II nut is processed for commercial use where size and color aren't as important. The cracking and sorting machinery is cleaned and disinfected at the end of each day of operation.
- 7 Processing of the kernels includes grading and sorting of whole kernels as well as chips and halves. The kernels and pieces are sold in raw form, roasted and salted, or coated in a variety of products. Conveyors carry the kernels to different stations. Raw kernels are packed directly in cans or boxes. Kernels to be roasted are separated into small batches of about 1 lb (2 kg) of nuts, coated in coconut oil, and cooked for about three minutes. Salt is mechanically sprinkled on the nuts, and the excess salt and oil are blotted off so the nuts will remain crisp and flavorful in their packages. Some processors use a dry roasting process rather than introducing additional oil.
- 8 Macadamia nuts that are to be made into candy are sometimes processed on site by the manufacturer or done off site by contractors. Chocolate coatings of milk and dark chocolate, various forms of brittle, and honey sesame coatings are among the most popular.
The cultivation and processing of macadamia nuts are persnickety by definition. Their unusual growing characteristics and their devilishly hard shells need careful attention. Quality control is essential in the orchard to produce nut clusters and collect them in a timely manner (and as cost effective as possible). During processing, machines are essential to remove both the husks and the hard shells, but observation is provided throughout by quality inspectors and by computer-controlled optical devices.
Kernels are also ground and processed to produce macadamia nut oil as a byproduct. Bad kernels are not wasted and are often used as animal feed. The shells and other waste comprise almost 70% by weight of the macadamia nuts, and they also are collected for other uses. The countries and regions that produce macadamias also usually grow coffee, and shells can be burned as a wood substitute in coffee roasting. The husks are ground to produce organic waste for gardening, for mulch in the nut tree orchards, and for chicken litter that, after use, returns to the orchard for use as fertilizer.
Macadamia nuts are an excellent source of iron, calcium, vitamin B, and phosphorus. Although they contain 73-80% fat, the fat is monosaturated or "good" and as acceptable as olive oil in many diets. Although macadamias have many healthful properties, their unusually rich flavor, crunch, and comingling with chocolate in a bounty of forms make them favorites among gourmets and snackers alike. Good taste is always in style, so the future of the macadamia nut is promising indeed.
Where to Learn More
Thomson, Paul H. "Macadamia." In Nut Tree Culture in North America. Richard A Jaynes, ed. Hamden, Connecticut: The Northern Nut Growers Association, Inc. 1979, pp. 188-202.
Sokolov, Raymond "Tough Nuts: Despite Some Superficial Similarities, Brazil Nuts And Macadamia Nuts Present A Study In Contrasts." Natural History (March 1985): 78.
California Macadamia Nut Society. http://users.aol.com/TecterJS/themac.html/.
Hamakua Macadamia Nut Company. http://126.96.36.199/hawnnut/.
Macadamia Miravalles S.A., Costa Rica. http://macadamia.co.cr/.
MacNut Farms & Café. http://macnut.co.nz/.
Mauna Loa Macadamia Nut Corporation. http://www.maunaloa.com/.
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