Chapter 5

Yeast and Winemaking

Inoculated Wine Fermentation

In most wine-producing countries conduct inoculated fermentations with selected S. cerevisiae strains with favorable oenological characteristics. There are many advantages that are noted of fermenting must with a pure cultured yeast strain instead of relying an indigenous flora. Some of the major advantages of inoculation with pure cultured yeast include faster fermentation rates, fermentation reliability, fermentation and style predictability, and fermentation and style repeatability (Section 5.2). Many commercial yeast strains of S. cerevisiae have special properties, as previously noted, allowing the winemaker to make small adjustments to the flavor or physical characteristics of the wine.

Sequential Inoculation

In general, non-Saccharomyces yeasts are not strong fermentors and tend to be easily overwhelmed once Saccharomyces begin to actively ferment. A sequential inoculation strategy of first adding a non-Saccharomyces followed by a selected Saccharomyces is the normal practice for some styles of wine. The biological control contribution of the non-Saccharomyces yeast in conjunction with the security of the S. cerevisiae enables winemakers to impact the sensory qualities and complexity of their wine while ensuring a reliable and complete fermentation. Winemakers who like the oenological qualities of indigenous non-Saccharomyces yeasts have two options available.

Commercial Non-Saccharomyces Yeast Strains

Winemakers who would like to utilize the oenological qualities of non-Saccharomyces yeasts have to rely on the spontaneous development of wild yeasts, with the inherent risks of unreliable fermentations and uncontrollable sensory deviations. Today winemakers can now utilize non- Saccharomyces commercial yeast strains such as Torulaspora delbrueckii, Metschnikowia pulcherrima, Metschnikowia fructicola, and Lachancea thermotolerans.

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