Genetic improvement of Torulaspora delbrueckii for wine fermentation

The use of Torulaspora delbrueckii has been repeatedly proposed to improve wine's organoleptic quality. However, this yeast has lower efficiency in completing wine fermentation than Saccharomyces cerevisiae since it has less fermentation capability and greater sensitivity to SO₂, ethanol, and CO₂ pressure. Therefore, the completion of fermentation is not guaranteed when must or wine is single-inoculated with T. delbrueckii. To solve this problem, new strains of T. delbrueckii with enhanced resistance to winemaking conditions were obtained. A genetic study of four wine T. delbrueckii strains was done. Spore clones free of possible recessive growth-retarding alleles were obtained from these yeasts. These spore clones were used to successively isolate mutants resistant to SO₂, then those resistant to ethanol, and finally those resistant to high CO₂ pressure. Most of these mutants showed better fermentation capability in base wine than the parental strain, and some of them approached the fermentation capability of S. cerevisiae.