The trees of the subtropical genus Macadamia, which are at most medium-sized (2 to 18 meters), grow very slowly. They are evergreen and bear long, wavy leaves in whorls. On their unbranched inflorescences, four-petaled cream-colored flowers produce 2 to 4 centimeter spherical drupes. Within each ripens a macadamia nut, a seed with an extremely hard brown shell and yellowish white, soft, and oil-rich (up to 80 percent) cotyledons. Commercially used are 3 non-poisonous species: M. integrifolia, M. tetraphylla and M. ternifolia.
Macadamias are East Australians, more precisely from Queensland and New South Wales, and now endangered there. First cultivations took place from 1888, around 1940 systematic overseas cultivation flourished in Hawaii. In 1997, Australia overtook the U.S. as the main producer, replaced by South Africa since 2012.
The plants prefer the temperatures, fertile, well-drained soils, and annual rainfall of subtropical tropical rainforests. From 7 to 12 years old, macadamia produces fruit year-round for many decades. Only the ripe fruits that have fallen from the trees are harvested from late autumn to spring. In the process, the fruit shell releases the seed from a longitudinal slit. Demanding macadamia culture is cost-intensive, hence the name "Queen of nuts".
The machine-cleaned "nuts" must dry (sun or oven), only then the shell can be opened with special tools. A gentle drying process and careful storage thereafter maintain the oil quality and mitigate enzymatic and microbial degradation. High-quality macadamia oil is cold-pressed light to golden yellow with mild nut aroma, refined almost colorless and organoleptically almost neutral. Extraction with solvents provides higher yields with lower ingredient retention.
Over 75 percent by weight of the seed consists of fat, a triglyceride mixture 60 to more than 80 percent monounsaturated fatty acid esters. In this, it surpasses olive and rapeseed oil. The basis for this, in addition to about 40 to 50 percent oleic acid, is a particularly high proportion of palmitoleic acid: up to 36 percent. Otherwise characteristic of animal fats. This, together with 11 to 16 percent saturated and a very low content of polyunsaturated fatty acids, makes macadamia oil highly heatable (smoke point 210 °C) and easy to store.
In the food sector, macadamia oil is a fine, mildly nutty edible oil and a valuable frying oil.
Macadamia oil is much more widely used in high-quality cosmetics. Oils with palmitoleic acid esters are very easily absorbed into the skin structure, known from mink oil, which is of concern under animal welfare legislation. Macadamia oil is an excellent substitute for the latter. It smoothes and cares for brittle, dry and sensitive skin in creams and lotions, as a fatty base oil, massage oil or fragrance carrier. Refined DAC qualities also perform this function in the pharmaceutical sector as a rich ointment base.
The genus name is a tribute to the Scottish-Australian chemist and politician John Macadam by the first describer in 1857, the botanist Ferdinand von Müller.
For dogs and cats, macadamia nuts are toxic, although usually not fatal.