Effects of ethanol on the temperature profile of Saccharomyces cerevisiae

Ethanol at concentrations above 3% (w/v) decreased the maximum temperature for growth of Saccharomyces cerevisiae in batch culture. At 9% (w/v), the highest concentration tested, the maximum temperature suffered a decrease of about 10 degrees centigrade. At effective concentrations ethanol shifted the ARRHENIUS plots of growth and death in the superoptimal temperature range to lower temperature while an associative temperature profile was maintained. Thus at a concentration of 6% (w/v), ethanol depressed the optimum temperature for growth from 37 degree C to 25 degree C, the final maximum temperature for growth from 40 degree C to 33 degree C and the initial maximum temperature for growth from 44 degree C to 36 degree C. The results indicate that during alcoholic batch fermentation these three cardinal temperatures are variables, the values of which decrease with increasing ethanol concentration. When the ethanol concentration becomes high enough to depress them successively below the process temperature, the yeast population becomes increasingly subject to ethanol-enhanced thermal death. Implications of the findings for the production of fermentation ethanol in batch and continuous processes are discussed.