THE GROWTH AND FERMENTATION OF A STRAIN OFS. CEREVISIAEWITH AMINO ACIDS AS NUTRIENTS

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Abstract
The amino acids of beer wort are the principal source of nitrogen for yeast. An acquaintance with the behaviour of yeast towards the various individual amino acids in as much detail as possible is therefore of considerable interest to brewing science even though our present knowledge of the actual amino acids occurring in wort and their amounts is rather limited. In the following paper an account is given of experiments wherein a strain of S. cerevisiae was grown under standardised conditions with amino acids as the sole source of nitrogen. From the observational data accumulated, four so-called nutrient characteristics have been evaluated for each amino acid; these are the rate of yeast growth, extent of yeast growth, rate of fermentation and the amount of nitrogen assimilated by the yeast from the amino acid. These characteristics afford a means of grading the amino acids according to their value as yeast nutrients. An ammonium salt has been used as the standard comparison nutrient. It has been found that these nutrient characteristics run parallel with each other: good growth is accompanied by good fermentation and vice versa. The majority of the amino acids have nutrient values about two-thirds as good as ammonia, although some are actually better than this standard. A few of them have no nutritive value at all. The nutrient value of an amino acid appears to be determined by the ease with which the yeast can split off its assimilable nitrogen, and by the inhibitive effect of the residue which is left behind after the yeast has assimilated the nitrogen.

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