INFLUENCE OF TEMPERATURE ON YEAST GROWTH AND FERMENTATION

Abstract

The total amount of sugar used when yeast is growing in wort consists of the sum of the sugar used in production of new yeast (“assimilation”) and that used in formation of alcohol and carbon dioxide (“fermentation”). The fundamentals of yeast growth in aerated wort are discussed in a mathematical treatment which shows that yeast yield and rate of sugar utilization depend upon the yeast growth coefficient (r) and the fermentation coefficient (s). Calculation of the growth and fermentation coefficients from various experimental data is illustrated. The value of each coefficient is strongly influenced by temperature, aeration, sugar concentration and other factors. The influence of temperature variations on each coefficient and on the total rate of sugar consumption (s + 0.476 r) over the range 20–43° C. is investigated, other conditions being standardized. It is shown that the fermentation coefficient increases steadily up to 40° C. (104° F.), after which it falls away steeply. The growth coefficient increases steadily up to 30° C, after which it increases only slightly up to 36° C. and then fells off steeply. The yeast yield calculated on total sugar used diminishes with increasing temperatures of growth, particularly with temperatures in excess of 36° C. (96° P.). 1951 The Institute of Brewing & Distilling