Macadamia nut quality

Tips on growing high quality macadamia nut kernel

There are three big quality issues that most NZ macadamia nut growers will face:

  1. Green Vegetable Bug (GVB), or Stink Bug. This bug (Nezara viridula) arrived from Europe before 1944. In winter the adults hide under bark or leaves. In spring they emerge to mate and lay eggs. These hatch into little stink bugs, then over a period of a couple of months go through about 5 moults before they become adults themselves. From the start of January through to Easter they have macadamia nuts on their menu. They sit on the ripening husk and their mouthparts get into the kernel through the husk and hardening shell. Damage appears during cracking as brown spotting and shrunken undeveloped kernel. There is visual and taste downgrade. Most commercial growers have resorted to using sprays, as there is no effective NZ predator. The bug can also be managed by planting  macadamia varieties less attractive to the Bug.
  2. Kernel discoloration. This is a mould which grows on one half of the kernel, giving it a slightly dark colour. The discoloration can be easily removed, and is mainly an appearance problem. This mould grows best when moisture content of nut-in-shell is above 10% and temperatures are warm and cosy. The sooner your nuts are dried to below 10% moisture content the better. Fresh nut-in-shell starts off at around 25% moisture content.
  3. Rancidity. Nuts will not keep forever. For air-dried nuts at ambient moisture content and summer room temperature, safe storage time is only about 2 months. Shelf life can be extended by drying down to the crunchy stage, and by storing them in cool dry conditions. Commercial growers vacuum pack kernel in nitrogen or CO2 at low temperatures (4 degrees). Home growers can store dried kernel in the deep freeze. They will not stick together because they contain no water. Rancid kernel has a distinctive stale smell and taste.
Green Vegetable Bugs
Green Vegetable Bug damage
Discoloration of kernel