The macadamia is an evergreen tree that grows in rainforests and in moist places with an annual rainfall of 1000—2000 mm. Macadamias prefer deep, fertile, well-drained soils with a pH of 5.0—6.5. As they are shallow-rooted, they do not suit areas of high winds. They are slow-growing, medium-sized trees, reaching a mature height of up to 12—15 m. With high rainfall, plentiful sunshine, and frost-free conditions, they will produce nuts after 4 or 5 years. Full production is reached in 12—15 years, and can continue for over 100 years when grown in suitable conditions.
Macadamia nuts are usually harvested manually after they have fallen, although some varieties need to be picked from the tree when ripe. Fallen nuts need to be harvested at least every 2—4 weeks, to prevent losses due to mold, germination, and pig or rat damage. The husks need to be removed within 24 hours of harvesting in order to reduce heat respiration, facilitate drying, and reduce the risk of developing mold. The nuts are dried until the moisture content is below 15%, and the shell is then removed.
Macadamia nuts are primarily cultivated for the kernel, which is usually oil-roasted or dry-roasted. Kernels are sold as snack nuts, and as an ingredient for ice cream and baked products. Macadamia nut oil has also become very popular in cooking. Its high smoke-point makes it very suitable as a frying oil, and it is a very stable oil, with an unrefrigerated shelf life of 1 —2 years. Macadamia oil's smooth texture and high oxidative stability make it especially suitable for use in soaps, sunscreens, skin-care formulations, and shampoos.
The kernel only accounts for approximately one-third of the macadamia nut, with the rest of the nut being the inedible shell and husk. These contain high proportions of lignin and cellulose, and can be utilized in products such as mulch, activated carbon used for water purification, and fuel for processing macadamia nuts; in plastic manufacturing; and as a substitute for sand in the sand-blasting process.
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