The optimal temperature for long-term storage of walnut seeds is between -3C and 0C. Low humidity is important too - for home and industrial storage.
The refrigeration technologies are not available in developing countries where walnuts are produced in large quantities. Because of that, walnut seeds are best stored below 25C. Temperatures higher than 30C, and humiditiy above 70% lead to fast and high spoilage losses. However the Mega Frut Walnut Kernels Company has the most advanced technologies to store huge amounts of production and keep its quality for long term periods.
Above 75% humidity, fungal molds that release dangerous aflatoxin can form.
Freshly harvested raw walnut seeds with water content between 2% - 8% offer the best color, flavor and nutrient density.