Influence of yeast autolysis after alcoholic fermentation on the development of Brettanomyces/Dekkera in wine
Brettanomyces, a contaminant yeast, is relatively common in wines and mainly in red wines during barrel aging. The results presented here relate to the effects of yeast lees autolysis on the growth of Brettanomyces. Experiments were realised in a culture medium after alcoholic fermentation, in a hydroalcoholic wine-like solution and in a red wine. Brettanomyces was inoculated at low level : 102 cfu/ml and the growth was controlled by counting on agar appropriate medium. Yeast lees from S. cerevisiae were added to these media in the presence or absence of an exogenous enzymatic preparation containing pectinase and β (1—>3) glucanase activities. Brettanomyces is able to grow in the synthetic media containing yeast lees. The addition of the glucanase preparation on yeast lees was correlated with an enhance in extracellular glucose level. This higher glucose level corresponds to the acceleration of hydrolysis of cell-wall glucans but was not correlated with a higher level of Brettanomyces population. This result confirms that this yeast multiply by fermenting very small quantities of glucose. In red wine the implantation of Brettanomyces is easy. With a low level of inoculation (102 cfu/ml), contaminant yeast grows rapidly to 106 cfu/ml (in 5 days). The presence of S. cerevisiae lees in red wine enhances significantly Brettanomyces population to 107 cfu/ml. During their development, these yeast produced less than 200 µg/1 of 4-ethyl phenol and 4-ethyl gaïacol. Volatile phenol content in red wine containing yeast lees were 3-5 times lower. Yeast lees have probably the particular property to being able to adsorb these volatile phenols by complexion with the cell-walls.
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