By Joshua Kato
• Ensure the drying and storage facilities maintain an even and adequate air flow. If heating is used during drying, do not use temperatures greater than 30ºC (or more than 5ºC above ambient temperature). Excessive temperatures during drying, particularly of nuts with high moisture content, can result in internal browning and discolouration of the kernel during roasting, and reduced shelf life. With heating, care is also required to reduce the risk of fire. It is essential to have a secondary controlling system to act as a fail-safe should the primary temperature controller fail.
• Avoid prolonged exposure to direct sunlight as it can cause rancidity and shell cracking, predisposing the nuts to contamination.
• Minimise drop heights to minimise fracturing and bruising of kernels. As the moisture content of NIS decreases, the kernel is more prone to damage and the acceptable drop height decreases. The maximum acceptable drop height at 10% m.c. is 2 m. Effective letdown measures need to be in place for drop heights greater than 2 m.
• Keep the fan operating continually when moist nuts are being added to the silo. Switch the fan off at night when the nuts have been dried to about 10% m.c. and the ambient relative humidity is greater than 60%.
• Nuts will be re-wet if fans are run when the relative humidity (RH) exceeds the RH in the silo. Use simple hand-held RH meters to measure the RH of the inlet and outlet air. Alternatively, more sophicticated and expensive automatic switching systems are available. Seek professional advice from consultants or manufacturers of drying equipment.
• Ensure the ducting for the fan inlet is high enough above ground level to reduce the risk of blowing wet air onto dry nuts.
• Duct air from within the shed, preferably from higher up towards the roof. This air is generally drier and warmer.
• Adequate venting at the top of silos is required to allow sufficient air movement.
• The bed depth in silos should not exceed 3 m.
• Completely empty storage vessels when consigning nuts or transferring nuts to other storage vessels.
