Breeding of Useful Killer Wine Yeasts

Abstract

For producing a good wine by pure culture as in brewing beer, useful killer yeast strains of Saccharomyces cerevisiae were bred by back-crossing KL-88, a wild killer sake yeast, with a repetitive parent, OC-2, one of the best wine yeasts.

Haploids of KL-88 were crossed with haploids of OC-2 to yield first-generation hybrids (1HYs). Haploids possessing both killing activity and SO₂ tolerance were selected from 1HYs and back-crossed with haploids of OC-2 to yield second-generation hybrids (2HYs). Several strains of killer hybrids were comparable to OC-2 in fermentation ability, SO₂ tolerance, TTC stain, and growth in a β-alanine medium at 35°C. One strain (2HY-1) was further confirmed to produce wine of as good quality as that of OC-2 in fermentation on a subindustrial scale.

The hybrids could kill only Saccharomyces yeasts in grape must. In the last stage of fermenting musts with the killer hybrid 2HY-1, no sensitive yeasts and few neutral yeasts (Kloeckera, Pichia, Hansenula, etc.) were detected; the former were killed by the killer yeast and the latter were markedly inhibited by the SO₂ added and the alcohol formed.

Furthermore, no film formation occurred during storage for 60 days at 25°C on the wine made with the hybrid because pseudo-film-forming Saccharomyces (S. bayanus, S. oviformis, S. fermentati, etc.) had been killed by the killer hybrid, whereas film formation was abundant on wine made with OC-2 unless SO₂ was added after fermentation.