Fermentation Basics

• Yeast is introduced to crushed grapes, called must, to start fermentation. Many specific strains of yeast are cultivated for winemaking that are capable of withstanding high fermentation temperatures and alcohol levels to make diverse types of wine. During fermentation, yeast transforms all available sugars into alcohol unless fermentation is stopped purposely to create a sweet wine with residual sugar. With large variations in styles of wine and types of grapes, alcohol content in wines varies from 8 percent to 17 percent.

Measuring Potential Alcohol

• Potential alcohol is determined by measuring the amount of sugar in a must before yeast fermentation is started. At home, this process is completed using a hydrometer. Fill a sample jar with settled and strained must and insert the hydrometer to learn the potential alcohol or Brix based on where the hydrometer sits when suspended in the must. This number, ranging from 0 to 20, shows how much alcohol is possible, as well as allows you to track how much alcohol has been produced during fermentation.

Tracking Fermentation

• Track the potential alcohol from the beginning of fermentation and throughout fermentation so that you are able to gauge the amount of alcohol in your finished wine. If your wine begins with a potential alcohol reading of 18 percent and you ferment it to 2 percent, you will have created a wine with 16 percent of alcohol with a small amount of residual sugar. For a dry wine, ferment the wine to 0 percent so that no sugar is left because it will all have been converted to alcohol.

Adjusting Alcohol Levels

• If your must does not have enough sugar to produce the alcohol content you desire in your finished wine, sugar can be added to the must to increase its potential alcohol. Use fine sugar for winemaking to ensure that it dissolves completely in the must. Sugar can be added at the beginning of fermentation or throughout fermentation to increase the alcohol content in the wine. Track the amount of sugar added and potential alcohol levels throughout the process to ensure that the wine fermentation is complete.