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“Stuck” Wine Fermentation Trigger Found by Researchers
- Updated: August 31, 2014
Whether making wine at home or purchasing a commercial product, one of the most common problems associated with the procedure is known as “stuck fermentation”. This occurs when yeast that is supposed to convert grape sugar into carbon dioxide and alcohol, shuts down prematurely. When this happens, remaining sugar is consumed by bacteria, leading to spoilage.
Recently, a team of researchers to include Linda Bisson, geneticist and professor in the Department of Viticulture and Eology from University of California-Davis (UC Davis), found the problem stemmed from a biochemical communication system. By working through a prion, which is a protein with an abnormal shape and one capable of reproducing by itself, this system allows bacteria found in fermenting wine to change yeast associated with sugar to other food sources yet without the yeast’s DNA being modified.
For years, experts have tried to identify how to avoid “stuck fermentation” and now according to Bisson, the goal is to identify different strains of yeast that in simple terms, ignore bacteria’s signal and do not form the prion but rather, continue on with the normal fermentation process.
As reported in the journal Cell, Bisson goes on to suggest that this discovery could also play a role in understanding metabolic diseases better, to include Type 2 diabetes. For years, biologists have been aware of a biological circuit found in yeast cell membranes capable of stopping yeast from using other carbon sources whenever sugar glucose exists. Inown as “glucose repression”, this circuit is most powerful in the yeast species called Saccharomyces cerevisiae, which allows people to use yeast for baking and winemaking.
As noted in this new study, the glucose repression circuit becomes interrupted sometimes when the replication of prions in yeast cell membranes are jump started by bacteria. This in turn starts the yeast-to-carbon sources process, excluding glucose, which makes metabolizing sugar less effective and slows down fermentation until it becomes “stuck”.
Organisms use a prior-based inheritance to help adapt to environmental condition although usually temporarily. However, heritable changes triggered by the prions make it possible for yeast to also revert back to their original way of operating if environmental conditions change again. With this study, researchers were able to demonstrate the process that causes “stuck fermentation” is beneficial to both the yeast and bacteria.
In this case, as metabolism of sugar slows, conditions in the fermenting wine become more conducive to the growth of bacteria. As a result, the yeast gains the ability to not only metabolize glucose, but also other carbon sources. This then maintains and extends lifespan.
Now that “stuck fermentation” is clearly understood, winemakers have a better chance of avoiding the problem. The goal is to alter levels of sulfur dioxide when crushing grapes, which helps to knock out the very bacteria responsible for triggering the unwanted process. Bisson concludes by saying that winemakers need to be careful when combining vineyard grapes know to have certain strains of bacteria or they can add specific strains capable of overpowering the bacteria from the grapes.