Abstract
Grapes of five white cultivars were crushed to provide a total of 104 samples of five cultivars. After centrifugation, several chemical analyses were performed on musts including an assessment of hydrogen sulfide (H2S) development during fermentation. Statistical evaluation established significant correlations (0.001 level) of: free amino nitrogen (FAN) with H2S and soluble solids; protein nitrogen with titratable acidity, turbidity, total nitrogen, and nonprotein nitrogen; ammonia nitrogen with soluble solids, titratable acidity, and pH; nonprotein nitrogen with turbidity and total nitrogen; and, finally, pH with titratable acidity. Considered the most important of these correlations was that between FAN and H2S. Subsequent fermentations, using nonfoaming yeast and protease, were each characterized by several distinct consequences including the stimulation of H2S. These experiments demonstrated that actively fermenting yeasts are capable of extracellular proteolytic activity and that the degradation of must proteins is implicated in the formation of H2S.
Clarification of settled musts by centrifugation had a small but marked effect. Bentonite treatment and removal of the bentonite-protein sediment before fermentation substantially decreased the development of H2S but adversely affected fermentation activity. By contrast, fermentations conducted in contact with bentonite stimulated both H2S development and fermentation rates, as did the pasteurization of must. Enhancement of the assimilable nitrogen content of musts resulted in the most effective control of H2S. Fermentation rates were accelerated, and, in some instances, suppression of H2S was complete.
It thus appears that the formation of H2S occurs indirectly as a result of the nitrogen demand of yeasts and not because of their sulfur requirements as such.
- Received April 1978.
- Revision received December 1978.
- Accepted January 1979.
- Published online January 1979
- Copyright 1979 by the American Society for Enology and Viticulture
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