Technical Working Paper 02-106

Energy Utilization And Microbial Reduction In A New Film Drying System, C.I. Nindo, H. Feng, G.Q. Shen, J. Tang and D.H. Kang February 2002

Abstract

Experiments were conducted with pureed pumpkin to evaluate energy efficiency and microbial reduction effect of a new thin-film drying method, Refractance Window^TM (RW) drying method. RW drying system was designed based on a novel concept that uses hot water circulating beneath and in contact with a transparent plastic conveyor belt on which thin film of pureed product is dried. In the energy study, heating water temperature, water circulation velocity, product temperature, and product moisture content was measured. In both pilot and commercial scale RW dryers with circulation water at 95°C drying of pumpkin puree from 80% to 5% moisture content (wet basis) was achieved in less than 5 minutes. The Refractance Window^TM dryer demonstrated 52% to 70% energy efficiency. The pilot scale unit was used to evaluate the effect of RW drying on microbial reduction. At a circulating water temperature of 95°, RW drying of inoculated pumpkin purees resulted in at least 4.6, 6.1, 6.0, and 5.5 log reductions of total aerobic plate counts (APC), coliforms, Escherichia coli, and Listeria innocua, respectively.