Yeasts in the Vineyard

It is generally accepted that in the case of sound fruit, population density and diversity of native (formerly referred to as wild ) yeasts is limited, ranging from less than 10 to 10 CFU/berry. The most frequently isolated native species are the so-called apiculate yeasts, Kloeckera apiculata, and its sexual counterpart, Hanseniaspora uvarum. These lemon-shaped small yeasts get their name from repeated budding at both poles (see Fig. 3-1) and often account for over 50% of the total yeast flora recovered from fruit. 

Other frequently encountered, but numerically less prevalent species, include Metchnikowia pulcherrima and its asexual counterpart Candida pul-cherrima, as well as Hansenula anomala, and Pichia membranaefaciens. The weakly fermentative pink (red) yeast, Rhodotarula minuta, is also relatively common. Occassionally, laboratory personnel isolate black yeasts. Black-pigmented fungi [Aureobasidium (Pullularia) pullulans], although yeastlike in appearance, are taxonomically separate (see the section 3.4.2). 

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). 

As grape sugars become available, Saccharomyces cerevisiae ind non-cere-visiae strains) populations increase. Harvesting equipment, including me- 

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Valero, E., Schuller, D., Cambon, B., Casal, M., Dequin, S. (2005). Dissemination and survival of commercial wine yeast in the vineyard a large-scale, three-years study. FEMS Yeast Research, 5, 959-969. 

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