The effect of oxygen on the survival of non-Saccharomyces yeasts during mixed culture fermentations of grape juice with Saccharomyces cerevisiae

Aims: The effect of oxygen on the survival of Torulaspora delbrueckii and K luyveromyces thermotolerans during mixed culture fermentations in grape jui ce with Saccharomyces cerevisiae was investigated. Methods and Results: Fermentations were carried out in two simple fermentat ion systems differing in the availability of oxygen. At low available oxyge n conditions, T. delbrueckii and K. thermotolerans began to die off after t wo days of mixed culture fermentation. In filtrates from 2-day-old mixed cu ltures, single cultures of T delbrueckii and K. thermotolerans survived and actively produced ethanol to concentrations of approx. 65 and 70 g l(-1), respectively, at low available oxygen conditions. Oxygen clearly increased the survival time and decreased the death rate of T. delbrueckii and K. the rmotolerans in mixed cultures, whereas it did not affect the growth and sur vival of S. cerevisiae. Conclusions: Our results show that the deaths of T. delbrueckii and K. ther motolerans in mixed cultures at low available oxygen conditions are not due to toxic metabolites produced by the yeasts but rather to the lack of oxyg en. Furthermore, they indicate that T. delbrueckii and K. thermotolerans ar e less tolerant to low available oxygen conditions than S. cerevisiae. Significance and Impact of the Study: Our study reveals new knowledge on th e mechanisms underlying the succession of yeasts during wine fermentations. This knowledge may be of importance when creating defined, mixed starter c ultures for the controlled production of wines with a wide range of flavour compositions.