Diagnostic Key Prevention of Fermentation Off-Character Production
Prevention of Fermentation Off-Character Production
Prevention of the formation of off-characters during fermentation can be tricky because production of these compounds varies dramatically by yeast strain. If the behavior of the yeast strain is known, nutrient management can be used to alter the pattern of formation of these compounds. Nutrients high in S-containing volatiles should not be used. In general such nutrients are not commonly marketed for the wine industry but if nutrients designed for a different commodity are purchased and used the S-amino acid content may be too high.
Volatile compounds produced during fermentation may be driven off by the carbon dioxide stream. Whether this occurs or not will be dependent upon the vigor of the fermentation post formation of the aroma compounds, the temperature and the volatility of the compound. Lower temperatures favor retention and higher temperatures favor loss. If wine sitting on the yeast lees starts to show evidence of the formation of these compounds the wine should be immediately racked off of the lees. With respect to ethyl acetate formation, the amounts made by Saccharomyces are inconsequential but the amounts formed by the acetic acid bacteria and Hanseniaspora uvarum can be so high that these compounds will not be lost from the wine during fermentation or subsequent processing. If the odor of ethyl acetate is noticed during a cold soak or other pre-fermentation treatment that treatment should be halted and the fermentation inoculated immediately. If a juice or fruit from a particular vineyard is prone to off-character formation then a strain not producing those characters should be selected.
It is also important to note when trying to select for formation of these compounds that they can be derived from biosynthetic or degradation reactions. These will occur at different times and under different conditions and again there will be considerable strain variation. It may be difficult to limit the formation of these compounds to the window that is positive.