October 2017

Wine fermentation

What is the impact of temperature on wine fermentation?

Dear Dr Vinny,

What is the impact of temperature on fermentation? Does colder or hotter fermentation result in a smoother wine? More acidic wine? Less alcohol?

—AJ, Los Angeles, California.

Dear AJ,

During fermentation – this magical process where the yeast converts the sugar in the grapes into alcohol – you have to take into account both the ambient temperature of the cellar and the residual heat which is a by-product of fermentation. Winemakers need to find Goldilocks’ sweet spot for both, where it’s neither too hot nor too cold for their ideal fermentation.

Hot fermentation is rapid fermentation. When it gets too hot, the yeast may start to die off, the fruit aromas may start to taste baked or cooked, and the aromas may be lost. Hot cultures also facilitate the growth of unwanted microorganisms.

While it seems that cold fermentation is preferred, many winemakers would agree. Cooler ferments are believed to preserve fruit colors, aromas and flavors. But too cold and the yeast can go dormant or get “stuck”.

Some winemakers like to start with hotter ferments and then cool them down, or vice versa, using their experience with their grapes to get more color and texture, to give the yeasts what they want so they don’t struggle before. to have finished doing it. their important work. Wine growers can use tanks with built-in cooling systems, or even just use ice to regulate temperatures.

When it comes to alcohol content, keep in mind that it is directly related to the ripeness of the grapes (and how much sugar they contain) and how much of that sugar is converted into alcohol. While a stopped fermentation means that there is probably some residual sugar that can still turn into alcohol, the fermentation temperature is not the main determining factor in the alcohol equation, rather it is the maturity. Grapes.

-Dr. Vinny

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