SOME EFFECTS OF WORT COMPOSITION ON THE RATE AND EXTENT OF FERMENTATION BY BREWING YEASTS

Abstract

The time required to ferment worts of varied composition to a given extent is dependent upon the extent of exponential growth in the early stages of fermentation; in the worts studied this is determined by the concentration of assimilable nitrogen. When the concentration of all the non-carbohydrate nutrients in malt wort is halved by dilution with carbohydrate, the addition of appropriate quantities of serine or arginine restores the rate of fermentation to that of the malt wort. Minor nutrients, other than amino acids specifically required by the yeasts used, are thus present in at least two-fold excess in the malt wort. The yeast produced during exponential growth in malt wort (sp.gr. 1·040) is able to ferment rapidly much greater quantities of fermentable carbohydrate than are present in that wort. The majority of the strains of yeast examined ferment equally well when either glucose or maltose is added to malt wort and do so whether the sugar is added prior to fermentation or towards the end; however, one strain fails to ferment satisfactorily if a substantial quantity of glucose is added to wort prior to fermentation, because of the subsequent failure of the yeast to adapt to ferment maltose. It is suggested that most brewing strains do not require to adapt to maltose utilization during the fermentation of wort.