Natural yeasts

Grape juice was fermented inadvertently into wine by natural yeast. To nomadic tribes, especially, it was welcome since it had flavor reminiscent of the fresh fruit or juice. In addition it could be stored and transported easily and remained drinkable from season to season. Eventually wine found its place as an article of commerce with necessary quality requirements. Not until the time of Louis Pasteur did the scientific foundation of winemaking become established and did enology become the science of wine. Since the early Pasteur experiments and discoveries winemaking has developed from a haphazard, ill understood, and risky... 

The condition of incoming fruit is always of the greatest importance and there will inevitably have been a certain amount of fermentation due to natural yeasts... 

Montrachet (University of California, 522), champagne (University of California, 505), Steinberg, and French White yeast are used most commonly in the North Coast, though other strains are available. The first two are widely available in dried form and the second two have come from Geisenheim Institute, Germany, and Pasteur Institute, Paris, respectively. The latter no longer supplies yeast cultures. Some wineries maintain their own cultures from year to year, and occasionally fermentations will be allowed to proceed with the grapes natural yeast population. 

Infante, J.J., Dombek, K.M., Rebordinos, L., Cantoral, J.M., Young, E.T. (2003) Genome-wide amplifications caused by chromosomal rearrangements play a mojor role in the adaptive evolution of natural yeast. Genetics, 165, 1745-1759. 

Heard, G.M. and Fleet, G.H. 1985. Growth of natural yeast flora during the fermentation of inoculated wines. Appl. Environ. Microbiol. 50, 727-728. 

Large numbers of natural yeasts (and other microorganisms) are found adhering to the fruit in the field. Originally these were the yeasts used to... 

Pichia stipitis. P. stipitis is the most effective natural yeast for the conversion of xylose to ethanol. This yeast species shares many characteristics with its close relative, C. shehatae. Toivola et al. [90] performed a systemic screening program with type strains of some 200 yeast species and identified P. stipitis as one of the yeast species that produces ethanol from xylose. There are many studies that have explored the property of this yeast in relation to its oxygen requirement, ethanol tolerance, enzyme cofactor s balance, etc. According to the reported literature [91,92], ethanol production from xylose by P stipitis exhibits the following characteristics ... 

The source of sugar varies. Grape juice is used to make wine, using natural yeasts on grape skins. Allowing fermentation to stop naturally produces a dry wine, with low sugar content. Stopping fermentation... 

OuGH, C.S. and M.L. Groat. 1978. Particle nature, yeast strain, and temperature interactions on the fermentation rates of grape juice. Appl. Environ. Microbiol. 35 881-885. 

Wine is made from crushed grapes. Unlike beer, no yeast needs to be added —the skins of grapes contain a natural yeast. 

A cool year or cool climate is characterized by a late and often insufficient maturity. Grape acidity is elevated and the musts are thus relatively protected against bacterial attack. However, there is a risk of botrytis attacks and the formation of oxidasic casse, since cool climates often correspond to rainy climates. In addition, grape crops arriving at the winery are often characterized by relatively low temperatures in cool years. As a result, the initiation of fermentation can be difficult, even more so when the grapes are washed by rain the natural yeast inoculation can be insufficient. 

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