Fermenting

The processes for making sparkling wines, white wines and red wines are much different. The white wine and red wine processes are discussed below.

White Wines

wine tanksMost white wines skip the destemming and crushing stage and go directly to the presses. The presses are used to gently squeeze the juices out. All skins and stems are removed at this point. They would add tannic flavor to the wine, and a color as well - neither are normally desired in white wine. The liquid is then held in stainless steel vats. In the vats, the sugars inside the grapes are turned into alcohol by yeast. Yeast is normally already present on the grapes, often visible as a powdery appearance of the grapes. The fermentation can be done with this natural yeast, but since this can give unpredictable results depending on the exact types of yeast that are present, cultured yeast is often added to the liquid. Many winemakers will intervene at this stage and inoculate the liquid and eliminate the natural or wild yeast so they have more control with the cultured yeast. This fermentation typically takes from 3-4 weeks.

wine tanksTemperature is very important during this stage - it also affects flavor and color. Often cooling pipes are run around the vats, to maintain the proper temperature. When the fermentation process is complete, white wine can then go through what is called cold stabilization. This process requires the wine dropping to almost freezing to precipitate out the tartaric crystals that can form. The crystals are quite harmless, and this process can affect wine flavor, but it is done so nervous consumers do not panic when they see crystals in their wine bottles.

Red Wines

wine tanksThe red wine grapes have gone through the stemming and crushing process and the liquid is left in contact with its skins to garner color, flavor, and additional tannins during the fermentation process. The combination of the liquid, skins and stems is called a "must". The must is put into an open top tank so the liquid can have contact with the skin and stems. The skins and stems rise to the top of the tank. How long the skins and stems are left in contact with the liquid and how often the cap is pushed down into the liquid is dependent on the type of wine being produced and the winemakers guidance.

red wine tankNext the liquid is moved to stainless steel vats for crisper reds, or in oak barrels for more mellow reds and the fermenting process continues. In whichever container, the sugars inside the grapes are turned into alcohol by yeast. As with white wines the natural yeast can be left in the liquid or removed and replaced with cultured yeast. This stage of the fermentation process can take from 10 days to a month or more. Once this stage of fermentation is completed, the clarification process begins. Winemakers have the option of racking or siphoning their wines from one tank or barrel to the next in the hope of leaving the precipitates and solids called pomace in the bottom of the fermenting tank.

Once the fermentation process is over, both primary and secondary, the grapes move into the most subjective process of the entire wine season process. How long do you give it additional aging in the vats and barrels before you move it to the bottles?

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(This site was created as the final project in Jeff Diamond's Dreamweaver A class.)

© 2009 Ron Boles (updated 3/2/09)