Labo VinChoosing the yeast
Nowadays, the yeasts are sold in a lyophilised form, in fine spangles. The only thing to do is to rehydrate them for 15 minutes in 10 times their volume of sweetened (5%) tapered (30° C) water to get a well alive and very active yeast culture, and pour it into the juice.
The yeasts used in wine making are divided in three species.
- Elliptical yeasts (Saccharomyces cerevisiae ellipsoideus). Numerous strains are available, whose different metabolic characteristics give the wine its character, and tolerating different alcohol concentrations (Bourgogne, Bordeaux, Champagne, Tokay, Sherry, Steinberg, Beaujolais, Porto, Haut-Sauternes, Malaga, Chianti, Lielfraumilch, Berncastler...).
- Saccharomyces bayanus (oviformis) bears high alcoholic concentrations (more than 18 % vol), but tolerate only a light sulfite rate (25 mg SO2/L). Temperature: 12-30° C. Those are "terminating" yeasts, used for bottle refermentation (sparkling wines).
- Schizosaccharomyces pombe is able to ferment malic acid and therefore to deacidify the wine.
Some recent strains contain besides the "killer" factor, which prevents the development of yeasts that do not contain it (wild yeasts).