FACTORS RESPONSIBLE FOR THE DECREASE IN pH DURING BEER FERMENTATIONS

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Abstract
The relative significance of factors which cause pH to decrease during fermentation has been investigated, using eleven yeast strains. Organic acid excretion and absorption of basic amino acids both have substantial effects: solution of carbon dioxide and absorption of primary phosphate contribute to a small extent. Buffering capacity, over the pH range 4 to 5, increases slightly during fermentation. Approximately 30% of the increase in hydrogen ion concentration cannot be attributed to known causes; direct excretion of hydrogen ions may be responsible. Fermentation with yeast propagated in semi-aerobic conditions rather than in fermentors gives beers of lower pH and increased organic acid content, but the latter factor is not in itself sufficient to account for the pH difference.