Location: National Peanut Research LaboratoryTitle: Oven drying times for moisture content determination of single peanut kernels
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2014
Publication Date: 5/14/2014
Publication URL: http://dx.doi.org/10.13031/trans.57.10438
Citation: Butts, C.L., Lamb, M.C., Sorensen, R.B., Chen, S. 2014. Oven drying times for moisture content determination of single peanut kernels. Transactions of the ASABE. 57(2):579-584.
Interpretive Summary: The standard method to measure moisture content of peanuts is to weigh a sample of about 200 grams, place it in an oven at 130 degrees Celsius for 6 hours, remove the peanuts from the oven, then weigh the dry samples. The percent moisture then be calculated from the initial wet weight and the oven-dried sample weight. However, there are some instances where it is necessary to determine the moisture content of a single peanut kernel using the oven method and this research was to see if less time in the oven may be required. Peanuts were rehydrated to various moisture levels by placing them in a sealed container at a constant relative humidity for at least 72 h. Individual kernels were weighed, then placed in an oven at 130 degrees Celsius. Each kernel was removed from the oven and weighed each hour for 6 hours and returned to the oven. After 24 hours in the oven, the final weight was recorded. This research showed that the average time required to dry single peanut kernels could be reduced to 5 hours and have an accuracy of 0.5% or less.
Technical Abstract: ASABE Standard S410.2: Moisture Measurement – Peanuts 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 6 h at 130 C for samples up to 30% wet basis. In previous research to calibrate instruments for measuring single kernel moisture, the moisture content of single peanut kernels has been 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, and the wet weight of each kernel was recorded, then placed in a convection oven at 130 C in individual containers. The weight of each kernel was recorded at approximately 90-minute intervals for 8 h, then again at 24 h. The apparent moisture content (dry basis) 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. 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% dry basis averaged 300 minutes for peanuts between 9 and 15% moisture content. The drying time for peanuts at 4±0.5% was approximately 150 minutes. This research showed that drying at 130 C for 6 h (360 min) is adequate for determining the moisture single peanut kernels and that ASABE Standard S410.2: Moisture Measurement – Peanuts is suitable for single kernel moisture measurements.