Evaluation of the effect of acid washing on the fermentative and respiratory behavior of yeasts by the acidification power test.

Fernandez, S.S., Gonzalez, M.G. and Sierra, J.A.

Abstract
Although acid washing is an effective method for removing contaminant microorganisms from the recovered yeast crop before reusing it for pitching, it is thought to have deleterious effects on the vitality and fermentative performance of the treated yeast, at least in some cases. In order to study these effects, samples of two brewers' yeast strains were acid washed at pH 3.5, 3.0, 2.5 and 2.0, after which the fermentative capacity and respiratory activity of the treated yeasts were evaluated by the acidification power test. The respiration of a second set of samples was studied using the Warburg technique. One strain suffered serious adverse effects from acid washing at all the pH values tested, while the other tolerated acid washing quite well at pH 2.5 or above, but was seriously impaired by washing at pH 2.0. Measurement of the carbon dioxide production rate showed a pattern of results very similar to those of the acidification power test. A direct relationship between oxygen uptake and acidification was observed in both strains. It was concluded that the acidification power test is well suited to the determination of the ability of brewers' yeast strains to tolerate acid washing.
Keywords : acid washing acidification brewers' yeast fermentation measurement performance tolerance