Why it matters to optimally de-husk nuts

Quality is increasingly becoming a determining factor to profitable macadamia farming and de-husking is a critical step that can significantly impact this and your bottom line.

Once harvested, macadamia kernels start to absorb moisture from the husk, causing them to swell. The longer one waits to de-husk, the more likely the kernels are to suffer bruising and breakage. Ideally, de-husking should take place on the same day as harvesting – if this is not possible then airflow through the nut in-husk can help to tide the time, but it should still be done within 24 hours of harvesting.

The husk of the macadamia is difficult to remove manually, making it necessary to use specialized machinery to process the nuts. The machine typically consists of a hopper, a rotating drum, and a fan or blower. The hopper is where the macadamia nuts are loaded into the machine, while the rotating drum contains blades or paddles that separate the husk from the nut.

There are several types of de-huskers commonly used in the industry, including mechanical, pneumatic, and electromagnetic, all of which use a mechanical means of removing the husk, typically a scroll or auger in combination with a chain that rubs against the husk to remove it.

The tension of the chain is usually adjusted with springs, which can be adjusted by a hand- adjustable bolt (mechanical) or through a cylinder and pneumatic pressure (easier to adjust). Some de-huskers also use rubber instead of a chain to remove the husks.

Mobile de-huskers are used in the field and can be cost-effective, as they reduce time and transportation costs. It runs off a generator, which makes it attractive during power cuts.

As the nuts and husks move through the drum, the fan or blower helps to separate them by blowing the lighter husks away from the heavier nuts. The separated nuts are then collected in a separate conveyor belt for further processing – sorting, floating, and drying – while the husks are typically collected in a separate container to be composted.

The choice of de-husker will depend on factors such as the scale of production, budget, and the specific needs and preferences of the producer. Each type has its advantages and disadvantages, and it is important to choose a machine that can effectively remove the husk while minimizing damage to the nut.

Key things to keep in mind:

Use the correct setting:

When the machine is set too tight one can damage the kernel or get nut breakages, and when it is not tight enough there may be too many reruns, increasing time, labour, and energy costs. This also increases the potential for more kernel damage due to the rough handling of the nut. Nuts from the same orchard differ in size between seasons. Do seasonal calibrations to ensure the correct settings per cultivar or even per orchard. Keep small nuts separate (sort to size before) and de-husk them separately on a different setting at the end of the day.

  • Service the de-husker frequently, at least once per season.
  • Inspect the product daily to ensure minimal breakages while also having as few as possible reruns.
  • Clean the product before de-husking to remove material such as leaves, sticks, and stones.