Definition - What does Alcohol mean?
The alcohol in grapes and wine varies dependent on varietal, ripeness, sugar and the fermentation process. After the grape sugars are fermented the amount of total alcohol content is called the potential alcohol. The type of alcohol found in wine yeasts is ethanol also known as ethyl alcohol, and they are the second major wine compound (water is the first).
WineFrog explains Alcohol
The alcohol content in most wine varies between trace amounts (less than 1%) in sparkling grape juice and increases to a maximum around 20% in port wine. Different types like Syrah and Zinfandels have the highest percentages typically ranging from 17-22%, Rosé and dry whites range between 8-11%, medium reds and sparkling whites are in the middle range of 9-14%. Some alcohol levels can have subtle differences in wines that have the same vintage due to variations in the fermentation process.
There are other alcohols present in wine, but their concentrations are so minimal that they usually cannot be measured, are eradicated during the fermentation process and only have slight influences on flavor. Labeling laws allow for 1.5% differences in bottling, so that accounts for why some bottles may taste different than other bottles of the same brand, varietal and year. Slight variances can also be caused by climate or region, for example a white wine from warmer regions will have a higher alcohol content than one from a colder climate.