Introduction to growing and processing macadamias


It is not widely know that the macadamia nut has its origins in Australia, however our ‘Australian Bush Nut’ was first discovered by Allan Cunningham in 1828. It wasn’t until the late 1880s that serious cultivation of these evergreen trees began.

The early 1900s marked the beginning of an exciting new industry, when a group of American horticulturists transported some macadamia seeds to Hawaii and began growing and grafting selections of these nuts to develop today’s agricultural success story.

It wasn’t until the 1960s that Australians realised the potential of this indigenous tree nut and began local cultivation. Trees, grafted from successful Hawaiian varieties, were brought to the rolling hills of North Eastern New South Wales and South Eastern Queensland where over 30% of the world’s production is now grown. Australian macadamias have developed a world-wide reputation for the finest quality, flavour and texture.

Growing Macadamias

Macadamia trees grow best in sub-tropical climates – the typical climate they have grown in for thousands of years. Most varieties start to bear commercially viable yields at 7 years of age, with trees taking approximately 12 years to reach full maturity and maximum yields of nut-in-shell. With careful management, trees can continue to yield well for many years. In fact some of the earliest orchards planted in the 1960’s still continue to bear well today.

Macadamia trees are produced by grafting a selected variety onto a seedling tree. This process involves specific skills and is carried out in specialist nurseries. It takes approximately 2 years to produce a fully grafted macadamia tree that is ready for planting in an orchard. Careful attention to good farm management during the formative years is critical – as it is a long wait before trees start to bear crop and poor management through this period can have long term impacts upon the orchards performance. In Australia approximately 250 – 300 trees are planted per hectare (depending on desired spacing) to create the neat and tidy plantations that are the hallmark of the Australian industry. Mature macadamia trees can grow to heights of 12 – 15 metres; they have dark, shiny leaves and bear sprays of long, delicate, sweet smelling white blossoms, called racemes.

The annual growing cycle takes some 9 months. The first flowering occurs in early spring with small ‘nutlets’ developing shortly after. These nutlets grow and develop through spring and summer – ripening in early autumn. Each spray of 40-50 flowers produces from 2 – 15 ‘nutlets’ and by early autumn large clusters of plump green nuts are very visible. Harvesting commences in late autumn and continues through the winter months.

Harvesting and Processing

Macadamia nuts are allowed to fall to the ground naturally. In some countries the nuts are harvested by hand but in Australia modern machinery is used to gather the nuts. Harvesters drive down the tree rows with the nuts getting picked up in the finger like wheels. After harvesting, the soft outer husk is then removed on the farm before the nuts are placed in storage awaiting delivery to the processing plant. The hard, round, nut-in-shell is transported to the factory where they are weighed and samples from each delivery are analysed by the laboratory for quality and moisture content. Nuts are placed into a drying system under carefully controlled conditions where they are dried down from a 15 – 20% moisture to a 3.5% moisture content – in preparation for cracking.

After drying, a specially designed cracker breaks the rock hard shell with minimal damage to the delicate kernel. Both shell fragments and kernel travel through an air separation system and through modern, hi-tech, electronic colour sorters which separate the shell fragments from the kernel. These sorters differentiate between the dark brown colour of shell and the creamy colour of the kernel and remove the shell fragments with a burst of compressed air. A second colour sort and a final hand sorting inspection is carried out, to remove poor quality kernel. In some countries electronic colour sorters are replaced by people.

Macadamia kernel is graded into ‘Styles’ numbered from 0 to 8 which represent the sizes of the kernel pieces. Style 0 is large whole kernel, style 2 is a mixture of wholes and halves, style 4 is primarily half kernels and higher numbers, 5-8 relate to various sizes of chips and small pieces. Once sorted into styles, the kernel is nitrogen flushed and vacuum packed into foil lined bags that are inside sturdy cartons, packed ready for sale. These cartons are stored in a climate controlled warehouse or cool dry areas ready for dispatch to manufacturers of various value added products such as chocolates, biscuits, snack packs and ice cream.