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Fermentation

February 7th, 2008 Posted in Fermentation, Winemaking

Fermentation is a very natural thing. It probably happened the first time when some grapes were lying around for too long. Because that’s all you have to do to. The wild yeasts that live on grape skins will start the fermentation process immediately. In the New World today, most wineries will kill off the wild yeasts with sulphur, and replace them with cultivated yeasts that are specialized to the grape variety, or to add a certain kind of flavor to the wine. This trend is catching on in the old world as well.

As the yeast organisms feed on the sugar in the must, the by-product is alcohol, carbon dioxide, and heat.  This is why the level of sugar in the grapes will indicate the level of alcohol in the wine. Yeast cells naturally die once the alcohol reaches around 15%, and then the fermentation process stops. Sometimes a winemaker may use sulphur to stop the fermentation process earlier than that, if they wish to leave a bit of residual sugar in the wine, which could make an off-dry, medium sweet, or fully sweet wine. In general therefore, the lower the alcohol level, the sweeter the wine will be. When the yeasts die off, they settle to the bottom of the tank and form a sediment called “lees.” You may have seen sur lee written on a bottle of Chardonnay– this means the wine was left on the lees to add additional complexity to the flavor.

  1. One Response to “Fermentation”

  2. By Dimitris on Aug 20, 2008

    Hello
    Congratulations for your website, it gives enough information for the hole process of winemaking and brings people closer to the wine drinking pleasure.
    I wish you could send me some information or some websites or papers that i can look for SWEET RED wine vinification. I would prefer the most professional you know.
    Thanks in advance

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