Selective hybridization of wine yeasts for higher yields of glycerol

Abstract

Wines that are lacking in body may be improved by the presence of greater amounts of glycerol. Wine yeast strains vary in their ability to produce glycerol. A programme of hybridizing yeast strains while selecting for increased production of glycerol was undertaken. Three generations of hybridization resulted in yeast strains which produced 10–11 g glycerol/L compared with 3.0–6.6 g/L produced by the wine yeast strains of the original breeding stock. Industrial-scale winemaking confirmed the ability of two hybrid strains to produce similar amounts of glycerol to those observed in laboratory-scale fermentations. The activity of the enzyme glycerol-3-phosphate dehydrogenase was measured in crude extracts of two breeding stock wine yeasts and in two final generation hybrid strains. The observed activities were lower in the products of the hybridization programme than in the original wine yeast strains. Two alternative explanations are suggested. (i) Selective hybridization may select for the alleles of the gene which codes for an alcohol dehydrogenase I isozyme which has a lower activity resulting in increased glycerol production. (ii) Phospholipid synthesis is reduced and the glycerol-3-phosphate, which is the major precursor of phospholipids in yeasts, accumulates as glycerol.