Oven Drying Times for Moisture Content Determination of Single Peanut Kernels

Abstract

<abstract><title><italic>Abstract.</italic></title> ASABE Standard S410.2 specifies that 200 g samples of peanuts should be dried in an oven until a constant weight is achieved. The standard recommends oven-drying at 100°C for 72 h or at 130°C for 6 h for samples with up to 30% wet basis moisture content. In previous research to calibrate instruments for measuring single-kernel moisture, the moisture content of single peanut kernels was determined using the same time and temperature recommendations as for 200 g samples. This study was conducted to determine if shorter oven-drying times could be used for single-kernel moisture determination. Shelled peanut kernels were rehydrated to five different moisture levels by placing samples over saturated salt solutions in closed containers for 18 d. A sample of 20 kernels was removed from the rehydration chamber, the wet weight of each kernel was recorded, and the kernels were then placed in individual containers in a convection oven at 130°C. The weight of each kernel was recorded at approximately 90 min intervals for 8 h and then again at 24 h. The apparent dry basis (d.b.) moisture content was calculated using the weight recorded at each observation. The error was calculated as the difference between the apparent moisture content calculated at each time step and the final moisture content calculated after 24 h in the oven. The data were fit to an exponential decay function to estimate the error as a function of drying time. The regression function was then used to estimate the drying time required to achieve various levels of accuracy. The drying time required to achieve an accuracy of ±0.5% d.b. averaged 300 min for peanuts between 9% and 15% d.b. moisture content, and this drying time was approximately 150 min for peanuts at 4% d.b. moisture content. This research shows that drying at 130°C for 6 h (360 min) is adequate for determining the moisture content of single peanut kernels and that ASABE Standard S410.2 is suitable for single-kernel moisture measurements.