Red wine is usually made from black grapes, but contrary to what you might think, the wine is not red because of the dark color of the grapes. In fact, the pulp of all grapes is the same color--clear. Red wines are dark in color because they receive some contact from the grape skins during the fermentation process. Red wine is fermented at around 68 degrees Fahrenheit. This is a bit  warmer than white wine, which encourages the  grape skins to bleed their color faster. As the grapes and their juice sit in the fermentation vat, the skins will rise to the top. If they just sit there, they won't lose much of their color. To solve this problem, most of the time the winemaker will perform something called "pumping over." In this technique, the juice is sucked out of the bottom of the vat, and then poured on top of the skins again, usually twice a day. Another method is called "punching down the cap," where someone gets inside the vat and pushes the skins down to the bottom. The danger of this method is that it can unpredictably release  large amounts of carbon dioxide, which would render the worker unconscious, and then he or she would drown in the vat.

The grapes will macerate with their skins typically for about 6 days for moderate tannin wines and 12 days or more for a highly tannic wine designed to be aged in the bottle for a long time before it is ready to drink. After this point the skin will be removed, and fermentation may continue longer, depending on the area and the nature of the grapes. The goal here with red wine is almost always to ferment away all the sugar, converting it to alcohol.

Some red wines undergo what  is called carbonic maceration. In this technique, the grape bunches are tossed into the vat without going through a crusher/destemmer machine. The grapes gradually burst and ferment on their own, without the use of additional yeast, once they fall off the bunch. This produces a very low tannin wine which is high in fruit character. This technique is classically used in the Beaujolais Nouveau produced in France.