Effect of soy skim from soybean aqueous processing on the performance of corn ethanol fermentation

► A soybean and corn integrated processing system was tested. ► Aqueous soybean process produces a skim by-product that needs to be fully utilized. ► Corn ethanol production needs water and readily available nitrogen for fermentation. ► The combination of the two systems reflects the best use of resources. ► Use of soy skim in corn ethanol fermentation increased initial fermentation rate and protein content of DDGS. The feasibility of using soy skim, a co-product of the aqueous processing of soybeans, in ethanol production from corn was evaluated. Specific growth rates were compared when Saccharomyces cerevisiae was grown in soy skim and peptone–yeast extract media supplemented with glucose. Such soy skim was proved to be a good nitrogen source for yeast growth. Next, fermentation of dry-ground corn to ethanol using soy skim as the media was simulated on 1.5-L scale. Replacing water with soy skim increased the initial ethanol production rates by 4–32% while final ethanol yield was about 39g/100g dry corn, similar to the result when water was used. Solid and protein contents in the finished beer increased with the addition of soy skim. Thus, replacing water in corn-ethanol fermentation with soy skim is feasible, and may improve the economics of both aqueous soybean processing and corn ethanol fermentation.