Yeast isolation from vineyard

Indeed, grapes are a primary source of microorganism, and many studies have shown that natural fermentation starts with those species predominant on grapes at harvest time (Fleet et ah, 2002). These can include the apiculate yeasts (Hanseniaspora uvarum and Kloeckera apicu-lata), Metschnikozvia, Candida, Pichia, Khodotorula, and Kluyveromyces. In contrast, although it is the main wine fermentation yeast, Saccharomyces have only rarely been isolated from vineyards (Martini, 1993 Martini et ah, 1996 Pretorius, 2000 Sabate et ah, 1998), since it is closely associated with the winery environment (Ciani et ah, 2004). 

Mortimer, R.K. 1995. Genetic Investigation Yeasts isolated from spontaneous fermentation of grape musts in California and Italy. Pract. Winery and Vineyard May/June 7-10. 

Strongly fermentative yeasts such as Saccharomyces cerevisiae are rarely found (or found at low numbers) on uninfected fruit, even in vineyards where fermented pomace is returned as soil amendments. Failure to routinely isolate Saccharomyces from the vineyard likely reflects its preference for high-sugar environments of grape juice and fermentation (Martini and Martini, 1990). 

Attempts to isolate either yeast from fruit in the vineyard have, with few exceptions, been unsuccessful. At least two reasons can be suggested for this failure (1) They are clearly fastidious, requiring reasonably complex sources of exogenous nutrients including vitamin supplementation. In clean fruit, proliferation would be very limited. (2) Attempts to isolate minority populations from mixed flora are often frustrated by the presence of numerically superior and/or more rapidly growing species. 

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