Macadamia trees grow to heights of 15m in fertile soils of sub tropical high rainfall areas. They have shiny dark leaves and bear delicate sprays of sweetly scented white flowers from which clusters of nutlets develop.
Mature macadamia nut kernels are encased in hard woody shells surrounded by green brown fibrous husks. They fall to the ground between March and September each year and are mostly harvested by mechanical harvesters at regular intervals.
The fibrous outer husk is removed within 24 hours of harvest to reduce heat of respiration and to facilitate drying. The husk material is usually recycled as organic mulch and the “Nut in Shell” is delivered to the processor.
Careful drying is a critical step in macadamia processing. At harvest the nuts have a moisture content of up to 30% and the kernel itself fills the entire shell. The drying process takes up to 3 weeks and during this time the moisture content falls to around 1.5% and the kernel shrinks away from the inside of the shell.
Modern machines have been developed to crack the tough shell of the macadamia and minimize damage to the precious kernel within. These include either a fixed plate and cutting blade or a combination of rollers and a base plate to compress the shell.
Shell separation and sorting
Methods of separating the kernel from the shell vary by processor and is usually achieved through the combined use of screens, air separators, flotation systems, state of the art electronic colour sorters and hand sorting. Sorting styles is mostly achieved by the use of gentle vibrating screens. At all points quality control is maintained to high standards – MIA is accredited to HACCP 9000.