STUDIES IN CONTINUOUS FERMENTATION I. EFFECTS OF YEAST CONCENTRATION

Abstract

Saccharomyces cerevisiae (NCYC 1026) was grown in synthetic medium, brewer's wort and media intermediate in composition, using both open and closed systems of continuous culture. The level of nitrogen source in the synthetic medium severely restricted growth in the open system but with similar flow-rates in the closed system much higher yeast populations were maintained. The levels of the ethanol and fusel alcohols in the spent media were not, however, commensurate with the difference in cell numbers but the total fusel alcohol production at higher yeast concentrations was about five times as great and that of ethanol was two-fold. With wort or an intermediate medium, the level of assimilable nitrogen was greater and in the closed system some of the nitrogen, particularly proline, was not utilized. Proline uptake was stimulated by increasing the level of carbohydrate in the medium or by increasing aeration so that more carbohydrate was diverted into metabolic pathways associated with growth rather than fermentation.