Investigating kernel moisture content at the front and back of semitraliers during peanut drying

Authors: Lewis, Micah; Trabelsi, Samir; NELSON, STUART - US Department Of Agriculture (USDA)

Submitted to: American Society of Agricultural and Biological Engineers
Publication Type: Proceedings
Publication Acceptance Date: 6/3/2016
Publication Date: 7/17/2016
Citation: Trabelsi, S., Lewis, M.A., Nelson, S.O. 2016. Investigating kernel moisture content at the front and back of semitraliers during peanut drying. American Society of Agricultural and Biological Engineers. ASABE Paper No. 162461643, American Society of Agricultural and Biological Engineers, St. Joseph, MI.

Interpretive Summary: Peanut drying is a postharvest process that is required to remove moisture from freshly harvested, unshelled peanuts. They must be dried to reduce the peanut kernel moisture content to 10.5% or less for sale and safe storage to prevent the development of mold and potential toxins produced by some molds. Even though left in windrows in the field to dry naturally before combing, peanuts still have 20% to 30% kernel moisture content when delivered to the peanut buying points. A recently developed microwave sensor can instantaneously provide the moisture content of the kernels in unshelled peanuts during the drying process. Therefore such kernel moisture sensors can be used to monitor kernel moisture content at different locations in the loads of peanuts being dried to study the uniformity of drying in loads of peanuts in drying wagons or semitrailers. Results of initial studies on drying uniformity are presented in this paper. Two peanut drying monitoring systems were field tested at a commercial peanut buying point in central Georgia. The monitoring systems were placed near the front and back of three semitrailers to monitor drying dynamics as the peanuts dried. The monitoring systems provided a continuous profile of kernel moisture content, temperature and relative humidity of the exhaust air, peanut bed temperature and relative humidity of the input air near the front and back of the semitrailer. Results showed that loading and distribution of foreign material can affect airflow through the peanut bed, causing a load of peanuts to dry nonuniformly. Of the three semitrailers tested, only one showed uniformity in drying trends near the front and back of the semitrailer. This study demonstrated the need for sampling or kernel moisture sensing at more than one location in the trailer. For one trailer, the kernel moisture content near the back of the trailer was almost 4% moisture content higher than that near the front of the trailer. The availability of monitoring systems at different locations in the semitrailer would provide buying point personnel with more information so that peanuts storage at excessive kernel moisture content could be eliminated or minimized for safe storage. This would improve peanut quality and safety by preventing the development of molds and aflatoxin for the benefit of the peanut industry and consumers.

Technical Abstract: The effectiveness of peanut drying can be influenced by many factors. Such factors include temperature and relative humidity of the air used for aeration, air velocity through the peanuts, and any obstructions to air flow caused by foreign material. Therefore, it is highly unlikely that a semitrailer holding 20 to 25 tons of peanuts will dry uniformly. During the drying process, an operator removes samples of peanuts for kernel moisture testing every three hours or so. Such testing is often used to validate the estimated drying time determined by peanut-drying models used in the peanut industry. However, if samples are taken only from one location, it is likely that other locations have higher or lower kernel moisture contents. To investigate kernel moisture content at the front and back of the trailer, two peanut drying monitoring systems were deployed at a peanut buying point in central Georgia. Each system monitored drying parameters and in-shell kernel moisture content in real-time, every 12 seconds. In-shell kernel moisture content was determined with a standard error of prediction of 0.55% moisture when compared to the reference oven-drying method. They were placed in 45-ft (13.7-m) drying semitrailers, one 10 ft (3 m) from the front and the other 10 ft (3 m) from the back. Data from the measurements were time-stamped and reconciled accordingly, and they were analyzed to compare the moisture loss in real-time at both locations in the trailer. The 12-second resolution provided a continuous moisture profile to analyze rather than the discrete profile usually provided by sampling every few hours. Results show that moisture loss, and therefore resulting kernel moisture content, is variable from one end of the trailer to the other in some cases. Therefore, systems that monitor peanut drying at various locations throughout the semitrailer would improve peanut drying efficiency.