Imbalance of pH and Potassium Concentration as a Cause of Stuck Fermentations

Abstract

The effect of the ratio of potassium to hydrogen ions on fermentation rate and progression was evaluated in conditions mimicking grape juice. A molecular K⁺/H⁺ ratio of 25:1 was found to be the minimum required for the completion of fermentation. Decreases in potassium concentration resulted in the failure to metabolize available glucose and fructose causing a stuck fermentation. If potassium levels were too high relative to the pH, the decrease in pH brought about by potassium uptake lowered the medium pH to a level at which it became inhibitory to continued fermentation. Thus, the ratio of potassium to hydrogen ion concentration will lead to a problem in progression of the fermentation if it is either too low or too high. The ratio of potassium to hydrogen ion did not affect rate of growth or formation of maximal cell biomass, but it did slightly impact maintenance of cell viability, which could be a contributing factor to the arrest of fermentation. Fermentation arrest was not detectable until three days post-inoculation; however, supplementation with potassium at that or later times did not restore fermentation rate. Grape juice at pH 3.3 or below may be at risk of premature arrest of fermentation due to a deficiency or excess of potassium, depending upon the buffering capacity of the juice.