Evaluation of Ethanol Tolerance in Selected Saccharomyces Strains¹

1 Presented at the 51st Annual Meeting, Milwaukee, WI, June 1985.

Abstract

Methodologies for the determination of ethanol tolerance were compared using four industrial yeasts. Ethanol was found to reduce the rates of growth and of fermentation in a linear fashion. Growth was completely inhibited near 12% ethanol (v/v), whereas only a 50% reduction in fermentative ability occurred at this level. Ethanol was also found to reduce cell viability but only at levels which had completely suppressed growth; the rates of viability loss were strain dependent. The ability of each strain to produce ethanol was assessed using 30° Plato wort under various nutritional conditions. The strains differed in attenuation and ethanol production, both of which were influenced by nutritional conditions. Differences in ethanol tolerance found using methods based on growth, viability loss, and batch culture performance all may reflect differences in the nutritional requirements and growth history of the yeast strain and the conditions of fermentation—not just ethanol tolerance. The method measuring inhibition of fermentative ability may be the best index of ethanol tolerance, as this characteristic is not influenced by nutritional factors or the culture growth phase. It also more closely reflects the upper limits of ethanol production reported in brewing and sake yeast. Yeasts within the genus Saccharomyces do not differ extensively in terms of their inherent ability to tolerate ethanol.

• Ethanol production
• Ethanol tolerance
• Fermentative ability
• High-gravity brewing
• Methods
• Viability