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Here you will find information about the different types of yeast involved with wine and grapes.  Choose your area of interest below:

 Yeast Genera Yeast Colonisation
Natural Yeasts

YEAST GENERA

There are thousands of yeasts blowing in the wind and living in the soil and on leaves, stems, vines and grapes. Of the 15 known genera, one in particular is favoured for winemaking. From the Greek words for sugar (sakchar) and fungus (Mykes), Saccharomyces is the genus that makes up most yeasts used in making bread, beer and wine. Seven species make up the genus, and the most important of these is Saccharomyces cervisiae, also called S. ellipsoideus, and its varieties.

The good yeasts (Saccharomyces cerevisiae) for winemaking include the strains Saccharomyces bayanus, Saccharomyces uvarum, Saccharomyces oviformis, Saccharomyces carlsbergiensis, Saccharomyces logo, Saccharomyces chevalieri, Saccharomyces diastaticus, Saccharomyces fructuum, Saccharomyces italicus, Saccharomyces hispanica, Saccharomyces oxydans, Saccharomyces pasteurianus, Saccharomyces prostoserdovii, Saccharomyces sake, Saccharomyces sterineri, and Saccharomyces vini predominantly. These varieties, or strains, tend to be naturally localized.

If one takes a pint of grapes from any vine almost anywhere in the world and crushes them, 50-75% of the yeasts naturally present will be one or more strains of Saccharomyces cerevisiae, Hansenula, Cryptococcus, Rhodotorula, Kluyveromyces, Pichia membranefaciens, and Torulaspora delbrueckii. One will also probably find at least 100 colony forming units per millilitre of Kloeckera apiculata (Hanseniaspora), Metschnikowia, Candida stellata, and Candida pulcherrima. Finally, a few Brettanomyces, Dekkera and Zygosaccharomyces bailii may also be present in the must.

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YEAST COLONISATION

When yeasts enter a new environment, they exist for a while in what is known as a lag period. During this period, which can last from minutes to hours, the yeasts basically test the environment to determine whether or not it is suitable for colonization. If they determine that it is, they end the lag period and begin reproducing. Yeast can reproduce at an alarming rate in a favourable environment. This rate, at least for a period, is typically one logarithmic unit per two hours, meaning that 1 yeast cell can theoretically become 8 in six hours, 64 in 12 hours, 512 in 18 hours, and 4096 in 24 hours. Luckily, when their population density reaches about 150,000,000 per millilitre of host liquid, they settle down and maintain a relatively steady population. This continues, all other conditions remaining constant, until they deplete all available oxygen, use up all available nutrients, or the alcohol they produce becomes intolerably concentrated. Most then die off, but if both oxygen and nutrients are still available then Brettanomyces, Dekkera and Zygosaccharomyces bailii, if present, may now decide to end their lag period and begin multiplying, ruining what would otherwise be an almost finished wine.

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NATURAL YEASTS

Wines fermented with natural yeasts tend to produce notable differences in the texture or mouth-feel of the wines, being; richer, rounder, "fatter" yet also possessing more delicate characteristics as well - a phenomenon difficult to explain given that "delicacy" and "fatness" are usually paradoxical terms.

Also wines that are fermented with natural yeasts demonstrated better oak integration, in that the oak influence tended to be less obvious.

Reduced "butter" character as a result of lower concentrations of diacetyl. All yeasts (which are still active towards the conclusion of fermentation) contain an enzyme which reduced the prevalence of diacetyl (which lends to the "buttery character"). Since natural yeast ferments last longer, the yeast stay in suspension longer, putting them in contact with the diacetyl as it is produced by bacteria.

Residual sugar levels tend to be higher in naturally fermented wines (1.5 grams per litre, compared to 0.9 grams per litre in wines fermented from commercial yeasts).

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