Location: National Peanut Research LaboratoryTitle: Temperature/Humidity Conditions in Stacked Flexible Intermediate Bulk Containers for Shelled Peanuts
Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2014
Publication Date: 7/15/2014
Citation: Butts, C.L., Lamb, M.C. 2014. Temperature/Humidity Conditions in Stacked Flexible Intermediate Bulk Containers for Shelled Peanuts. ASABE Annual International Meeting. ASABE Paper No. 141846655,St Joseph, MI. 10PP (doi:10.13031/aim.20141846655).
Interpretive Summary: After shelling and sizing, peanuts are loaded into large sacks called totes for handling, storage, and transport to the manufacturer of peanut products. The sacks hold approximately 1 ton of shelled peanuts with a value of approximately $1350 per tote. In recent years, shellers have had to shell peanuts year round through the hot summer months and immediately after shelling, the totes are moved directly into a cold storage facility that is maintained at 38 degrees and 65% relative humidity. The manufacturer buys the peanuts in shipments of 20 totes and the totes are removed from cold storage, set out in a dry storage area and allowed to begin to equilibrate to ambient conditions. The totes are then loaded into a truck and transported to the customer. Some loads have been rejected by the customer due to mold, excessive moisture, or sprouting peanut kernels in the top of the tote. If these conditions are observed in one tote of the 20 tote shipment, the customer rejects the entire shipment. If this occurs, then the sheller must pay for shipping back to the shelling plant for reprocessing or dispose of the peanuts. Many times, if this happens to an international shipment, the entire shipment is disposed of costing the sheller almost $28 thousand. A series of studies were conducted in June and July of 2012 where peanuts were loaded into totes with 3 different levels of breathability (Low, Medium, High). The peanuts were loaded and sensors were placed inside the top of the tote to record the temperature and relative humidity during cold storage, tempering, and shipment in trucks. During these tests, no mold growth or other deterioration was actually observed. To determine the risk of modl growth, the moisture content that the peanuts would reach, also known as the equilibrium moisture content (EMC), was calculated for each temperature and humidity reading. The time that the EMC exceeded two 8% was calculated for each tote to indicate the risk of mold growth in the top of the tote. The risk of mold growth was strongly influenced by the temperature and humidity conditions when the peanuts were shelled. The peanuts that were shelled and placed in cold storage in July had almost twice the risk of mold growth as those shelled in June. This was true during cold storage and during tempering. The peanuts shelled in July had 3 times the risk of mold growth during the transit from tempering to the customer. In general, the risk of mold growth tended to decrease as the breathability increased.
Technical Abstract: Shelled peanuts are loaded into flexible intermediate bulk containers, or totes. After loading, the 1000-kg totes are placed directly into cold storage at 3ºC and 65% relative humidity until shipment to the customer domestically in the United States or internationally requiring transport overseas. In recent years, shellers have had to shell peanuts well into the hot, humid summer months, and have received customer complaints of excessive moisture, mold growth, or sprouting in the top of the totes upon arrival of the peanuts at their final destination. The American Peanut Council specifies that the breathability for the body and top panels should have a minimum breathability 22 and 40 cfm, respectively. Two tests were conducted in commercial shelling and cold storage facilities using 2011 crop peanuts and 3 totes from each of 3 suppliers. Supplier 1 failed to meet the breathability specifications. Supplier 2 exceeded both body and top panel breathability specifications. Supplier 3 met the top panel specification and exceeded the body panel specification. Peanuts were shelled, sized, and loaded according to normal practice and placed in cold storage for 50 d, removed and tempered in ambient conditions, then placed in a closed van to simulate over-the-road transportation. Temperature and relative humidity were recorded in the top of each tote and used to calculate EMC. The time that the calculated EMC exceeded thresholds was affected by time of year that the peanuts were shelled, and tended to be lower when the ratio body:top breathability of the was at least 1:1.