Grape juice environment

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). 

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. 

Whole grapes immersed in a carbon dioxide atmosphere, poor in oxygen. They are the most affected by anaerobic metabolism. In addition, they are located in an environment with an increasing ethanol concentration. At a certain partial pressure, ethauol diffuses into the berries in anaerobiosis. At pressing, the press juice has a higher alcohol content than the juice from a solely anaerobic metabohsm. 

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