Primary fermentation is the process that turns grape juice into wine through a series of chemical reactions. To put it simply, yeast (a microorganism) turns the natural sugar in the grape juice into alcohol and carbon dioxide (bubbles). After the grapes are harvested and their juice is extracted, the winemaker can use the natural yeast found on the grape skins or add cultured yeast to start the fermentation process. Yeast needs heat to work, and around 45F it will start feeding on the sugar and turning it into alcohol and CO2. The higher the sugar content, the higher the alcohol content the wine can achieve. The winemaker can stop the process by chilling the wine to under 40F, where the yeast cannot survive. It will die naturally if the wine reaches more than 17% or the temperature is more than 120F. Apart from alcohol and bubbles (which in most wines disappear to the atmosphere), fermentation creates biproducts like aldehydes, acids, esters, and sulfides, that can add aromas and textures to the wine. The process can last from 5 to 20 days, and the earliest evidence of grape fermentation was found in the country of Georgia and dates back to 6000BC!
Author: Maytte Rivera
