NON-VOLATILE ORGANIC ACID AND pH CHANGES DURING THE FERMENTATION OF DISTILLER'S WORT

The only non-volatile organic acids found in significant amounts in distiller's wort were citric and malic acids. During the fermentation of penicillin-treated wort by yeast, the levels of citric and malic acid remained unchanged, succinic acid appeared and small amounts of lactic acid were also found. Without added penicillin, citric and malic acids disappeared, succinic acid was produced as before and lactic acid appeared in large amounts especially towards the end of the fermentation period of 65 hr. After 16 hr. fermentation, the pH of penicillin-treated wort had fallen from 5·6 to 3·6; by 40 hr. it had risen to 4·2 and by 65 hr. to 4·4; without added penicillin the changes up to 40 hr. were similar but the final pH at 65 hr. was 3·8. These pH changes are considered to be due first to the production of organic acids and loss of wort buffering power during the period of rapid yeast growth, secondly, to a period of yeast autolysis which returns to the fermenting liquor phosphate buffering capacity and, finally, to wash lactic acid.