Alcohol is an essential component in wine. It gives wine body and flavor. There are a number of compounds that are “alcohol”. The “alcohol” that is in wine is correctly called ethanol. Ethanol is also the alcohol that is in beer and distilled beverages.
Alcohol in wine is the result of the conversion of sugar in the must (the pressed grape juice) by yeasts. The yeasts (which are a form of fungus) consume the sugar and produce alcohol and carbon dioxide, which bubbles out of the must as it becomes wine.
The yeasts that produce fermentation in wine are mostly the same yeasts that are used in bread making. That’s why bread is a common aroma when wine is being made and is a typical aroma in sparkling wines, which commonly rest on the dead yeast beasties (called “lees”) for extended periods. The more sugar in the must, the more potential alcohol can be produced. Most yeasts (and there are a tremendous number of different yeasts) can produce wines up to about 16% to 18% alcohol naturally.
Above that, the alcohol kills the yeast beasties and the fermentation stops as a result. It takes a lot of sugar to make a wine with this high alcohol. Most grapes are not that ripe. A few that can be that ripe are grown in very warm climates like Muscat grapes in Australia and Zinfandel grapes in California’s Sierra Foothills. These wines can have very high alcohol levels and significant residual sugar (commonly called “rs”) because the yeast beasties got killed off by the alcohol when it got to 16% to 18% and did not consume all the available sugar.
Fortified wines have alcohol added to them in the form of distilled spirits (commonly brandy). The addition of alcohol to a must that is partially fermented results in wine with significantly higher alcohol and residual sugar, since the added alcohol kills the yeast beasties before they consume all the sugar. The most common fortified wines are Port, Sherry, Marsala, Madeira and Vermouth. There are also some excellent fortified wines from Banyuls and Maury in Southern France. Dry Sherry, Marsala and Vermouth wines have the alcohol added after the fermentation is complete, resulting in dry (sugar levels that are below the threshhold of perception) wines.
Article re-printed from Bend Wine Cellar