Effects of Brewers’ condensed solubles (bcs) on the production of ethanol from low-grade starch materials

Abstract

Yeast fermentation was performed on grain and bakery byproducts with and without adding the same volume of brewers’ condensed solubles (BCS). Starch material in the grain and bakery byproducts effectively was converted to fermentable sugars with conversion ratios of 93–97% by successive treatments of samples with bacterial αamylase and fungal glucoamylase. The yeast fermentation of these enzyme-digested byproducts alone showed that ethanol concentrations of 16.4–42.7 mL/100 g dry solid in the broth were achieved with fermentation efficiencies of 87–96%. Addition of BCS to the grain byproducts increased ethanol concentration by 10–86% by increasing the potential glucose content of the broth. The rates of fermentation measured by CO₂ gas production demonstrated that BCS addition to bakery byproducts reduced the fermentation time from 62–72 h to 34–35 h. In bakery byproducts that were low in amino nitrogen, exhaustion of nitrogenous compounds in substrates was found to be a limiting factor for yeast growth. Because BCS is a rich source of nitrogen, adding BCS to these substrates markedly increased the fermentation rate.