Vitaltitration used for predicting fermentation performance of ethanol stressed brewing yeast

Résumé

Obtaining different batches of beer with the same characteristics each time is a continuous challenge for brewers worldwide. Besides the complexity and natural variation of ingredients´ composition, reusing the same batch of yeast up to 7-10 times makes the brewing process even more difficult to control. The pitching brewing yeast should have a high metabolic activity in order to meet the expected fermentation performance. Aiming to determine the fermentative performance of brewing yeasts stored under ethanol we have used a vitality assay. The physiological state of yeast cells stored for 72h in the presence of ethanol was evaluated in terms of vitality, measured as CO₂ production and H⁺ extrusion. Two widely used European industrial brewing yeast strains, Saccharomyces lager W 34/70 and Saccharomyces ale W 210, were stored in conditions similar to the ones used for industrial brewing yeast cream. Our results show that the Saccharomyces ale W210 strain can be stored for larger storage periods than W34/70, but the ethanol stress should be of maximum 7.5% (v/v) ethanol to have an acceptable loss of cells’ vitality during storage. These informations can be valuable for fermentation performance prediction of the two tested industrial brewing yeast starter cultures, as well as for a correct dimensioning of the yeast inoculum.