Drying nuts after harvest

DRYING Hazelnuts – By Jenny Horwell

New Zealand has the advantage of good soil and good air for growing good hazelnuts.

We all spend time choosing varieties, planting trees, then watching the sticks grow into trees and getting excited about the few nuts that fall after a couple of years.  The next year there is some work involved as a lot more nuts fall and then about year 7 it becomes… “What are we going to do with all these hazelnuts”.

There doesn’t seem to be a lot of information out there about what to expect when trees reach maturity. Quantities of nuts to expect, how to harvest and dry them. It always seems to be a shock when we find a carpet of nuts on the ground and the big question of “what do we do now”.

The simple answer is get them in an airy situation as quickly as possible.

It’s quite easy to think about a soft, moist kernel sitting in a tight shell. If it isn’t in a situation that is warm or airy it is just going to sit there and sweat and turn mouldy, especially in the middle of a bag. These nuts in turn cause the nuts around them to go mouldy, and eventually affect the whole sack.

Nuts will often fall before or after rain as well as on good sunny days.  Hazelnuts have the advantage of being enclosed within their shell and a little more resilience to water but they don’t tolerate dampness.

  • They need to be dried in a spot that has good air flow and preferably out of damp weather.
  • A shelving system with a small mesh is ideal.
  • If the mesh is too large for the nuts partly filling smaller onion sacks and lying them on racks can work
  • In both these cases, it is important not to stack the nuts too thickly and to move them around so all the nuts get a good airing.
  • Hanging nuts in half filled sacks also works but again, these need to be moved around every time you walk past them to keep an even airflow around the nuts.

A few things that cause kernel to deteriorate

  • Collecting nuts too late in the season after they have been lying in leaves, long grass or dewy mornings
  • Drying in bags on a veranda is not ideal if the weather is damp as the kernel will absorb the dampness
  • bags sitting in a room with no airflow is also not an ideal situation. The nuts are lying on top of each other in a bag with no airflow and will result in a mouldy kernel.
  • Leaving nuts covered under tarpaulins will make the nuts sweat
  • Mixing rubbish from the ground and bad nuts in sacks with good nuts will give poor kernel quality.

Thicker shelled nuts, Ennis, Barcelona, Tondo varieties, Merville are difficult to dry naturally and get a good kernel, especially with the autumn temperatures.

The best solution we have found for these varieties is using air driers. It will depend on the climatic conditions while drying and the condition the hazelnuts arrive at the driers but these varieties will take over 48 hours to reach a stage where they are dry enough for storage.

Whiteheart have a thinner shell and require less stringent drying conditions but, if not treated properly, will be no different to the thicker shelled hazels and have mould.  As a comparison in the driers, whiteheart will take just over 24 hours to reach storage dryness.

In air driers, it is not ideal to have onion sacks filled to brimming.

It’s all about airflow.

It is better to have them filled so they will spread out completely flat and the air can move evenly through them.

If the bags are tightly filled air will escape around the ends of the bag and not flow well between the nuts in the bag.

Nut kernels may lose up to 30% moisture, but this is not a hard and fast figure.  A simple test for moisture is to monitor a Kilo bag of nuts.  It will lose weight as the moisture levels drop in the kernel and the weight will eventually level off.

There are also various moisture meters that can be used to test the moisture levels.

A huge amount of effort goes into harvesting nuts and it’s worth the extra effort to dry them properly to prevent mould and keep them safe for eating.