It is widely accepted that active dry wine yeasts (ADY) must be rehydrated before addition to musts. Current rehydration procedures are over 15 years old and may not be optimal for the approximately 200 strains commercially available worldwide. Temperature, water hardness, sugar concentration, agitation, and rehydration duration did not have a major effect on the recovery of fermentative activity in three yeast strains differing in rehydration behavior and/or lag phase. Early indicators of yeast activity during rehydration were then investigated. We correlated pH, carbon dioxide release, and trehalose utilization with the early stage of fermentation. Results showed that the recovery of fermentative activity by ADY can be measured early and easily by rehydration indicators, particularly changes in pH and carbon dioxide release.
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