Yeast kicks off the fermentation process in wine making. After adding it to your must, it begins to consume the sugar, producing equal amounts of ethanol and carbon dioxide.

There are wild yeasts everywhere around us, including on the skins of grapes if you’re making wine from fresh fruits. Generally, winemakers discourage these yeasts from fermenting by adding sulfites to kill them off before they can get started. This is done so the winemaker has more control over the fermentation and can produce a consistent wine from batch to batch.

There are basically two types of wine available to home winemakers; liquid and dry.
Most homemade winemakers prefer to use dry yeast. It’s easier to store and to work with.
A subject of debate among homemade winemakers is whether or not to re-hydrate the dry yeast you’re working with. I’ve found that re-hydrating is really not necessary and in fact can lead to problems if the process is not done exactly right.

Two things that can adversely affect the performance of your yeast are the temperature and also the oxygen level. In order to achieve a proper, vigorous fermentation the temperature needs to be maintained between 70 -75 degrees. There are exceptions and variations to this. Some white wines are fermented at lower temperatures to enhance certain flavors, but special yeast is used to do this.

Oxygen is needed during primary fermentation because the yeast are multiplying rapidly during this stage and without air this multiplying can be severely restricted. During primary fermentation the use of an airlock is discouraged so the wine can get all the oxygen it needs. Primary fermentation lasts approximately 7 days and 70 percent of the fermentation is complete at this point.

During secondary fermentation the wine is usually placed in another vessel with an airlock attached. The airlock is to allow carbon dioxide to escape while preventing bacteria and other micro-organisms. The reduced exposure to air also gets the yeast to stop multiplying and put its energy into making alcohol.

Yeast is a crucial part of homemade wine making. The more you learn about yeast and the fermentation process, the more you’ll be rewarded wine batch after batch of consistent, delicious homemade wine.