Much of the red wine production process involves extraction of color and flavor components from the grape skin.
Handpicked or machine-harvested grapes are usually tipped into a receival bin when they arrive at the winery and conveyed by a screw mechanism to the grape-processing equipment.
[citation needed] On arrival at the winery, there is usually a mixture of individual berries, whole bunches (particularly with handpicked grapes), stems, and leaves.
Crushers usually consist of a pair of rollers, and the gap between them can usually be regulated to allow for light, hard, or no crushing, according to the winemaker's preference.
The must is then pumped to a vessel, often a tank made of stainless steel or concrete, or an oak vat, for fermentation.
Macerating enzymes (for instance glucanases) may also be added at this stage, to aid extraction of color and fruit flavours from the skins and to facilitate pressing.
Many winemakers, however, prefer to control the fermentation process more closely by adding specially selected yeasts usually of the species Saccharomyces ellipsoideous.
In order to encourage efficient extraction of colour and flavour components, it is important to maximize contact between the cap of skins and the liquid phase.
There are exceptions, such as the case of sparkling wine production in regions such as Champagne, where grapes are traditionally whole-cluster pressed with stems included to produce a lighter must that is low in phenolics.
[citation needed] A second microbiological transformation commonly takes place after the alcoholic fermentation of red wines.
[citation needed] Once the MLF is complete, the red wine is usually racked (decanted) off its lees (dead yeast cells and other solids), and has sulfur dioxide preservative added to avoid oxidation and bacterial spoilage.
Some red wines, particularly those designed for early drinking, are cold stabilized so as to prevent the precipitation of unsightly tartrate crystals in the bottle.
[citation needed] Most wines are filtered at some stage before bottling, although some winemakers use the absence of filtration as a marketing tool.
[citation needed] Europe and North America are significant consumers of red wine, with variations in purchasing behaviors among countries.
Americans prioritize grape variety when buying wine,[8] while Spaniards focus on the AOC,[9] [clarification needed] and Swiss consumers seek the best price.
[18] Since red wine contains alcohol, it can have detrimental effects on the liver and pancreas, worsen gout symptoms, and cause strokes when drunk excessively.