Comparisons between a Commercial Wort and a Waxy Sorghum Wort Fermented into Lager Beer, with Emphasis on Yeast Growth and Ethanol Production

Abstract

Substrate and product profiles were compared during lager beer fermentations of a commercial wort and a wort produced from waxy sorghum grits inoculated with yeast cultured in wort or yeast-malt media. A bioreactor with 1-L capacity and strict temperature controls was used to ferment the hopped wort. The reactor was designed to sample the fermenting wort. The number of suspended cells of Saccharomyces cerevisiae, pH, soluble solids, and fermentable sugars were determined. The resulting fermentation kinetic profiles for worts produced from waxy sorghum grits were comparable to those for the control wort. Beers produced from waxy sorghum grits had comparable pH, reducing sugars, and number of yeast cells. The highest number of suspended yeast cells was reached after 60 hr of fermentation for both fermenting worts. Production of ethanol followed the same trend during 144 hr of fermentation. The final concentration of ethanol was slightly higher than the expected values found in commercial American lager beers because the starting wort was adjusted to 14°P instead of 12°P. This study clearly demonstrated that worts produced from barley malt and waxy sorghum grits are a suitable substrate for S. cerevisiae and that refined waxy sorghum grits are suitable brewing adjuncts for production of lager beers.