The macadamia nut tree is a fast-growing, medium-sized evergreen tree with heavy, dark green foliage that hails from Australia. Its leaves – which are blunt tipped, oblong, and generally a foot or more longer – develop in either whorls of twos, threes, or fours, but are rarely solitary. Macadamia flowers are small and whitish, hassled and growing on long spikes, while its nuts can ripen throughout the year, though they primarily ripen in the fall and the spring. The nut has a leathery case that is 1 inch in diameter, containing either a spherical nut or two hemisphere nuts. They also have a smooth hard shell that encases a white kernel.
While macadamia nuts originate and are grown in Australia, commercial production is mainly in Hawaii. Some countries in Latin America, Africa, and Asia also grow macadamia nuts, while trees can be found in California and Florida for the continental United States. The highest quality macadamia kernels are not only free of defects or insect and fungal damage, but also contain at least 72 percent oil. The kernels with less than 72 percent oil are usually immature and harder and will over-brown when roasted.
Macadamia nuts are harvested manually after falling, which occurs for eight to nine months of the year in Hawaii (July to March). On relatively even land, large-scale producers use mechanical sweepers and pickup devices to offset the high cost of agricultural labor. CTAHR has developed a tractor-mounted pickup device that works for smaller orchards. To prevent losses from mold, germination, and animal damage, macadamia nuts should be harvested at least every four weeks during rainy weather, though they don’t need to be harvested as frequently during dry weather.
Unhusked nuts should not be stored for more than a day. Rather, it is best to husk the nuts immediately and either air dry them or take them to the processor the next day. In cases where the nuts were picked and cannot be husked or deliver to the processor, the in-husk nuts should be dried, by spreading them on a wire or slotted rack that is out of the rain and in direct sunlight. While the shell accounts for most of the macadamia nut’s weight, with Hawaii’s average kernel recovery rate being around 23.5 percent during 1989-1990, an improved cracking system, along with better shell-kernel separators and high kernel cultivars, could raise the recovery rate to 35 percent.