Studies on the Alcohol Tolerance of Yeasts

That microorganisms grown in culture will eventually cease growth and sometimes die is known to all who have carried on pure culture work. Cessation of growth may be due to one of three factors: (1) depletion of nutrients, (2) unfavorable environ-mental conditions, or (3) the so-called "staling effect " which is due to the accumulation of products of the organism's own metab-olism. When cessation of certain physiological activities occurs even when environmental conditions are favorable and there is an ample supply of nutrient materials in the medium, it is evident that this cessation is due to the third of the above-mentioned factors. It is a well-known fact that in the commercial produc-tion of alcohol by fermentation there is a certain alcohol concen-tration which cannot be exceeded, regardless of the amount of sugar supplied to the yeast cell. It is obvious that after a certain period the yeast is no longer able to produce alcohol, and, since fermentation always stops about when the same alcohol concen-tration is attained (if the same yeast strain is always used), it is logical to assume that for every strain of yeast there is a maximum alcohol concentration above which the yeast ceases to function. A number of workers have observed that different yeasts will vary in the amount of alcohol they produce (e.g., distillery yeasts and wine yeasts); these differences might possibly be due to differences between the yeasts in their abilities to tolerate alcohol. Of course, during the alcoholic fermentation many substances other than alcohol are formed, but ethyl alcohol and carbon dioxide are