Wine Wednesday: Fermentation

By: Cecily G

Happy #WineWednesday, fellow wine-os! A few weeks ago, we discussed the importance of grape harvest, and what steps go into this vital process. (Catch up here!) Last week, we discussed the steps that follow harvest, when the grapes go through a process known as crush. (Catch up here!). Today, we are going to continue this by discussing what goes on after the grapes have been crushed and pressed. The next step in the wine-making process is known as fermentation, when grape juice begins to turn into wine.

To start, what exactly is a wine fermentation? A fermentation is when yeasts (that are present on the skins of the grapes, or added by the winemaker) start to consume the sugars in a wine, and convert them into alcohol and carbon dioxide.

Image via

Grapes come into the winery with naturally occurring yeasts on their skins, so once the grapes are crushed and the juice is exposed to these yeasts, and once the juice is at the right temperature, fermentation begins. Many times, predictable, cultured yeasts are added to the juice as well. This gives a little more control to the winemaker, as yeasts can affect the timeline of fermentation, flavor characteristics of the resulting wine, and more.

Red wines require a temperature of 78-86 degrees Fahrenheit, as this will help stimulate the extraction of pigments from the skins. Any warmer, though, and the yeast will die in the heat. White wines require 53.6 - 59 degrees Fahrenheit; cooler temperatures preserve delicate flavor characteristics that could be destroyed in higher temperatures.

White wines are typically fermented juice only, meaning the juice is separated from the skins and solids of the grape. On the other hand, red wines usually ferment while still in contact with the skins and solids of the grapes they came from.