Wine Making - Fermentation

Ahhh, fermentation - this is the phase in the winemaking process that really gets wine going on its path to its ultimate destination ... the bottle! It is during fermentation that the grape's sugars are converted to alcohol (specifically ethyl alcohol) and carbon dioxide, along with a good bit of residual heat that needs to be monitored to prevent distortion of flavors. The process of red wine fermentation typically takes place in stainless steel tanks, large vats or oak barrels. Maceration is basically the contact phase - where the must and the grape skins have maximum contact to produce good red wine color, structural tannins and extensive flavor components and nuances. The more the red wine grapes are in contact with their grape skins, the "bigger" the wine will likely be.

White wine fermentation often takes place in stainless steel tanks with lower heat levels that are closely monitored and the oxygen levels strictly guarded (to prevent rapid oxidation). Chardonnay is one exception, some winemakers prefer to hold the Chardonnay juice in sealed oak barrels for fermentation to influence flavor development.

If during the fermentation process the grapes were not quite ripe enough, sugar may be added to the must to increase alcohol levels in the final product, this addition is referred to as "enrichment". Likewise, acid can also be added to the must if the acidity is low, this is understandably referred to as "acidification." Also with white wine fermentation an additional step referred to as "stirring the lees" is added. This step involves mixing up the residual yeast that is left post fermentation to yield more flavors.

There is another type of fermentation called Malolactic Fermentation.

Malolactic fermentation is a process in which lactic acid bacteria converts the harsher malic acids (think green apple pucker) in the juice into lactic acid (think creamy milk) to produce a softer mouth feel and overall a more inviting palate presence. Most red wines go through malolactic fermentation to reduce their acidity and some fuller bodied white wines are sent through malolactic fermentation (usually in the barrel) to mellow them out a bit more.