by Gordon and Jean Leidner
All wine contains alcohol. That is stating the obvious. But did you know that the alcohol content in wine can range from 7 to 20%? What causes this variation? Which wines typically have a lower alcohol content and which have a higher? How can you tell how much alcohol is in a bottle of wine?
How Much Alcohol?
We’ll answer the easy question first. Federal law requires all wine bottles to list the alcohol content on the label. Wine with an alcohol content between 7 and 14% is considered a “table wine,” and an alcohol content of 14% or more is considered a “dessert wine.” However, as we will see later, many of these wines aren’t technically dessert wines at all.
Variations in Alcohol Levels
What causes such a wide variation in alcohol levels? To answer that question let’s start with a short lesson in how grape juice becomes wine. Grape juice turns into alcohol through the process of fermentation. Grapes on the vine are naturally covered with yeast. When the crushed grapes are put into a container at the right temperature, a simple chemical reaction occurs. The yeast turns the sugars in the juice into alcohol and carbon dioxide. Voila! Wine!
Causes of Variations
Now, to the original question: “What causes such a wide variation in alcohol levels?” Why does a German Riesling, for instance, have a low alcohol content (under 12.5%) while a California Petite Syrah can have over 14.5% alcohol? It primarily has to do with the amount of sugar in the grape. Sugar is produced in the fruit as it ripens on the vine. The more sugar in the grape at harvest time, the more sugar there will be in the juice for conversion into alcohol.
In cool climates, such as Germany, where the vines struggle to ripen their grapes, sugar levels are minimal, and consequently, the alcohol levels are lower. California’s sunny, warm climate produces grapes with higher sugar content because the fruit ripens easily.
In addition to climate, the variety of grape makes a difference; some grapes naturally produce more sugar than others. For instance, Grenache and Zinfandel grapes have high sugar content and ferment into wine with a higher alcohol content.
A winemaker can use several methods to boost the sugar content in wine. One technique is to let the grapes get overripe on the vine before harvesting, which is how late harvest dessert wines are typically produced. Another technique is to let the grapes freeze on the vine—which causes some of the water to be squeezed out of the grape—resulting in a higher residual sugar content. These grapes are then used to produce “ice wine.”
A third technique to increase sugar content is to interrupt fermentation. This is done by adding a distilled spirit to kill the yeast, a process known as fortifying, (the way Port wines are made) or by chilling the wine and filtering to remove yeasts (the way Italian Moscato and German Auslese wines are made). Finally, extra sugar can be added during wine making in a process called chaptalization.
Alcohol Content in Types of Wines
See the table below for general guidelines regarding alcohol content in different types of wines:
|Wine Type||% Alcohol|
|Red: Cabernet, Pinot Noir, Merlot||12-14.5%|
|Red: Zinfandel, Syrah, Petite-Syrah||14-20%|
As an indication of alcohol content, check out the “legs” in your next glass of wine. You may recall from last month’s post on Wine Terminology that the thickness of the “legs” that run down the inside of the glass has to do with the amount of alcohol in the wine.
Swirl your wine in the glass and hold it up to the light. You should observe tiny rivulets running back down the glass. This is caused because alcohol evaporates faster than water. The alcohol crawls up the glass as it evaporates, but since there is a film of water on top, it is pushed up in an arch. Eventually gravity wins, the water’s surface tension is broken, and down run the legs.
I hope you learned some fun new facts about fermentation. Now it’s time to take your newfound expertise with you to the wine store and do some experimenting!
Gordon and Jean Leidner have been wine enthusiasts for years. They enjoy visiting wineries, hosting wine parties, and have even dabbled in making wine from kits. Gordon has been a history buff for most of his life, and blogs at his website Great American History.