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.

Making Wine - Crushing and De-stemming

The second step in wine making series is Crushing and De-stemming the grapes.

After the grapes have been harvested it is often a mad dash to get them crushed and destemmed. The objective of crushing is not necessarily to squeeze all of the juice out of the grape, but to split the external skin and allow the juice to start its run, giving the sugar from the juice its first chance to mingle with the natural yeast found on the grape's skin. It's the combination of yeast and sugar that produces the wine's alcohol, via the yeast converting the sugar to alcohol and carbon dioxide. The "crush" happens in one of two ways - again by mechanical means with a heavy spiraled steel roller or the more traditional approach that you see in all of the fun Italian wine-themed movies - the famous grape "stomp."

At this point the grape stems are separated from the juice, or "must" as it is referred to at this phase in the game. This is also the juncture where red wine grapes and white wine grapes take different paths. If a wine is destined to be a red wine then the grape skins (not the juice, which is virtually clear) that provide the color characteristics and the tannin contributions for a red wine. However, if the goal is a white wine, then the grape skins are removed along with the stems at this phase of the process and the grapes are pressed prior to fermentation.

Pressing The Grapes

Pressing, usually done right after the crush for white grapes and after fermentation for red wine grapes, is basically taking the sticky grape solids left from either the crush or fermentation and squeezing them to get a very thick liquid that can be used to enhance both color and flavor of the presumptive wine to be.

Stay tuned for our next posting on Wine Fermentation.