Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/1997
Publication Date: N/A
Citation: N/A Interpretive Summary: Within the peanut industry, blanching is the term given to the process of removing the seed coat or skin from shelled peanuts before they are roasted for uses such as peanut butter or salted peanuts. The process consists of heating peanuts to dry them slightly and then removing the loosened seed coat from the peanut. Common thought in the peanut industry is that the process results in a decrease in shelf-life of peanuts. Because so many peanuts are processed in this way, it is important to understand the process and the results of the process on peanut quality so that potential for improvement may be determined. The work reported here examined the temperature changes that occurred in the bed of peanuts while they were heated in nine different time/temperature protocols which bracketed the standard protocol used in the industry. The work demonstrated that significant variation in temperatures occurred within the peanut bed during all the heating process and that peanuts generally do not reach the maximum setpoint temperature. The magnitude of the temperature variation was related in a predictable fashion to the final oven setpoint and the length of time peanuts were in each heating zone. The study indicated that reduction in moisture content to less than 4% from a beginning moisture content of ca. 5.5% resulted in maximum blanching percentages of 71-75%.
Technical Abstract: Medium, commercial size, runner type peanuts were heated in an air flow direction-controlled, lab scale oven to simulate an industrial multizone dryer used in peanut blanching. Nine blanching protocols consisting of three heating times (30, 45, and 60 min) factorially paired with three final oven setpoint temperatures (76.7, 87.8, and 98.9 C achieved from 32.2 C over six heating zones) were tested for effect on blanchability, moisture content, and temperature variation within individual seed and within the bed of peanuts. Temperature through the peanut bed varied as air flow (76.2 m/min) was reversed in alternating zones. Bed temperature variation during the heating process was highest in the 30 min protocols and the maximum difference between the top and bottom of the bed reached 17.6 C. Temperature variations decreased in the 45 and 60 min protocols, however, maximum differences as high as 8.1 C were consistently found. Seed temperature variation was as much as 5 C between the seed surface and 3.14 mm into the seed. Seed moisture decreased from ca. 5.5% to a low of 2.94% in the 60 min/98.9 C protocol. Blanchability, defined as the percent of seed with total seed coat removal, reached an upper limit of 71 to 75% in the 45 and 60 min protocols at 87.7 C and all of the protocols at 98.9 C. Blanchability was correlated with final oven setpoint temperature and final moisture content when moisture content was above 3.8%.