Fermentation
Fermentation is initiated by yeasts, which consume the grape sugars and produce alcohol. The yeast may be added from commercial preparations, or it may be found naturally on the grapes. Commercial yeast additives produce very consistent results year over year, while naturally occurring yeasts are more difficult to manage and take longer but can result in complex and unique aromatics.
In red wine fermentation, the juices must be stirred or punched to submerge the skins, since they naturally float. The different mechanisms extract varying amounts of flavors and can produce wines with different characteristics.
In some white wines, vintners can bypass some racking steps and leave much of the lees (sediments) in place. They’ll typically stir their wines during fermentation in order to maximize contact with the sediment, a process called bâtonnage. Wines that are aged in this fashion, with the sediment, typically have more complexity and flavor and are referred to as Sur Lie.
Pressing and Aging
After most (or all) sugars in the wine have been converted into alcohol, fermentation is complete. In commercial operations, this step will usually take somewhere from 5 days to 3 weeks to complete, but some extreme examples may take up to 4 years. Homemade wine, in contrast, usually takes between 1 and 4 months, usually because the fermentation conditions and yeast activity aren’t as precisely controlled.
White and blush wines are pressed before fermentation, so once fermentation is complete, they’re moved directly to barrels for aging. Most aging barrels are stainless steel or oak. Oak is used to impart specific flavors to wines, and in some cases, oak staves or chips may be added to a stainless-steel vat to get the same effect. Other “barrels” may be concrete, glass, or even clay. Each type of barrel has a unique influence on the finished wine, but oak has the most noticeable, leaching organic compounds into the wine that give it vanilla notes. As the concentration of organic compounds lowers over time, older oak barrels require longer aging periods. Concrete and clay tanks, on the other hand, reduce acidity.
Aging time may range from 6 months for white wines, or up to 30 months for dry, red wines. The longer a wine ages, the more chemical reactions occur, which further affect the wine’s flavor and body. Some describe red wines as tasting smoother and nuttier as they age.
Secondary Fermentation
The second fermentation of red wine (and some white wines, like Chardonnay) happens as the wine settles after pressing. Known as malolactic fermentation, a number of bacterial processes occur, but lactic acid bacteria assumes primacy, consuming malic acid and producing lactic acid, which has a creamier, buttery, or even chocolatey taste.
Finishing, Mixing, and Bottling
Finishing in winemaking is the process of stabilization and settling after fermentation. Cold or heat stabilization can be used during the fining process to clarify the product. Fining is an optional process, primarily used for aesthetics. It involves adding substances like cream of tartar or bentonite, which binds to proteins in the wine and allows them to settle out. After a few days, the settled particles are removed in another racking.
Blending wine is a step that relies almost entirely on art and experience, rather than strict science. A blend may involve mixing samples of different grape varieties, different vineyards, or even just different barrels of the same vintage to produce a finished product. This process adds complexity to the wine’s flavor and texture, creating a unique vintage that’s better than its parts. Some blends follow a traditional recipe, while others are freshly developed and reflect entirely new flavor characteristics.
Bottling wine is a relatively simple process, but no less important than the previous steps. Primarily, the goal is to maintain optimal cleanliness while reducing or eliminating exposure to oxygen, since oxygen accelerates aging.
The shape of a wine bottle has no effect on the quality, longevity, or flavor of a wine, although there are some traditional shapes and colors associated with different wines. As far as color, if your wine is expected to be left out where it will be exposed to UV rays from the sun or florescent lights, for example, green or amber bottles are a good choice. These colors absorb UV rays which would otherwise accelerate the oxidation process.
