Black grapes are used. In all but a few varieties, the color comes from the skins, which is why it is possible using certain techniques to make white wine from red grapes.
   The destemmer removes the stems and the crusher breaks open the berries to release the juice without squashing the pips, which can contribute bitter flavors to the wine. For some red wines made from less tannic red varieties such as Pinot Noir, some or all of the stems are retained to add structure to the wine. Generally though the stems are removed because they tend to make the wine astringent.
   Fermentation vessels vary enormously in size, shape and material depending on the type and quantity of wine being made, and the resources available to the winery. Most red wine is made in large tanks made from steel or sometimes lined concrete or fiberglass. In more modern wineries, these are fitted with some means of regulating the temperature. Heat is needed to extract the components from the crushed grapes but overheating can make the wines taste 'soupy'. The yeast needed for fermentation may be selected from commercial preparations and inoculated or, less commonly these days, fermentation may start spontaneously thanks to ambient yeasts in the winery and on the grapes.
   The CO² created during fermentation causes the skins and pulp (known as the cap) to float on top of the juice and a variety of different techniques are used to keep the cap and the juice mixed up. The large open-top wooden vessels used generally for top-quality red wines do not generally impart any oak flavors but they do allow gentle oxidation, which helps the fermentation.
   When alcoholic fermentation is complete, malolactic fermentation usually follows. This converts harsher malic acid into softer lactic acid.
   There is a range of different types and sizes of press used to separate the wine from the solids but most modern ones are pneumatic, allowing the winemaker to control the pressure and avoid extracting bitter tannins from the seeds.
   Some top-quality red wines are matured in oak barrels for 12 to 18 months or so. The barrels vary in size and age. The younger and newer the barrel, the more oak flavor is imparted to the wine. In addition to this effect on the flavor of the wine, oak barrels allow slow oxidation of the wine, which tends to soften the tannins and help clarify the wine. It also means that the barrels need to be topped up regularly to protect the wine from overexposure to oxygen. (Slow and controlled oxidation is generally beneficial. Overexposure can turn the wine to vinegar.)
   Most red wine is not aged in barrels. Instead it is transferred to a tank and fined with a fining agent to remove very small molecules such as proteins so that they do not form a haze in the bottle.
   Some red wines, especially those that have matured in a barrel, are bottled without filtration. These wines may over time form a harmless sediment in the bottle. However, most wines are filtered to some degree to clarify and stabilize the wine so that it remains in good condition after bottling.

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