Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 22, 2001
Publication Date: April 1, 2002
Interpretive Summary: Peanuts are dried (cured) in bins using heated air. The air temperature is controlled by a thermostat capable of maintaining a constant temperature. New control equipment is capable of calculating and controlling the plenum temperature in response to changing ambient conditions. The guidelines for drying air temperatures were developed primarily in VA/NC growing region where the ambient temperatures are cool. Peanut harvest in Georgia, Florida, and Alabama occurs from late August through the end of September. Maximum temperatures are usually in the low to mid 90's making the conditions much different in the southeast than in VA/NC for drying peanut. Tests were conducted using 4 different methods to calculate the drying air temperature. The conventional control (CC) method set the drying temperature 15F above ambient air temperature. Two drying rate control methods (DRC1 and DRC2) set the drying air temperature based on the moisture content of the air (H, lb water/lb air). The fourth control metho set the drying temperature so that the relative humidity of the air after it was heated 45% (RHC). The temperature setting for all four methods could not be higher than 95F. The DRC2 dried peanuts fastest at an average of 0.78%/h compared to 0.60%/h for the CC. Split kernels and kernels with- out the skins was no different. DRC2 can be used to dry peanuts faster in the southeast without serious detrimental effects on peanut quality.
Technical Abstract: The introduction of affordable control networks for peanut dryers has made it posible to vary the curing temperature based on ambient conditions. Peanuts from the same field were cured using 0.11m3 dryers to approximately 10% w.b. Plenum temperatures (Tp) for each dryer were controlled using: 1) Conventional Control (CC): Tp=Ta + 8C, not to exceed (NTE) 35C; 2) Drying Rate Ctonrol 1(DRC1): TP=15.699 - 201.46H.1n(H), NTE 35C; 3) Drying Rate Control 2(DRC2): Tp=21.699 - 201.46H.1n(H), NTE 35C; 4) Relative Humidity Control (RHC): Tp=T such that RHp=45%, NTE 35C. H represents the humidity ratio of ambient air (kg water/kg air). Peanuts cured using DRC2 cured significantly faster (0.78%/h) compared to peanuts cured using DRC1 (0.42%/h) and RHC (0.53%h). The DRC2 drying rate was not significantly greater than with CC (0.60%h). Milling quality as indicated by percent splits, percent bald kernels, and shelled stock value were not significantly different. The percent split kernels were not significantly and averaged 10.2% in samples cured using CC, DRC2, and RHC while DRC1 averaged 8.7%. Shelled stock value ranged from $959.89/Mg using DRC2 to $978.74/Mg using DRC1. Peroxide values, free fatty acids, and flavor ratings were acceptable for all curing treatments. Seed germination was not significantly different, and ranged from 82.8% to 87.3%.