With few exceptions, all grapes produce white juice. When red grapes ferment with their skins—a mixture referred to as “must”—the juice acquires color, ranging from pink (rosé) with short contact to deep red when contact is prolonged. Accordingly, the order of processes used to make red and white wines differs.
For white wines, winemakers crush grapes, press them to separate juice from skins and then ferment the juice. Most winemakers separate grapes from their stems before crushing, but some press whole bunches for white wines to limit oxygen exposure and facilitate a crisp quality in the final wine. There are some limited exceptions, however, where white grapes will have a short period of skin contact to add some complexity.
For red wines, winemakers crush grapes enough to break open skins, ferment the juice with skins in the mixture in a process called “maceration” and then press the must after fermentation is complete to separate juice and skins. In some cases, before fermentation, winemakers crush red grapes and place them in a cold environment to prevent fermentation for a few days. This process, called “cold soaking,” allows the juice to collect extra color and flavors from the skin.Some red grapes undergo “carbonic maceration,” a special process whereby winemakers ferment them in whole, uncrushed bunches. Used for some wines in France’s Beaujolais and Côtes du Rhône regions, the winemaker places bunches into fermentation vessels and fills the empty space with carbon dioxide. With limited oxygen, an intercellular fermentation begins inside grape skins using the grapes’ own enzymes rather than yeast. Regular fermentation with yeast completes the process to produce light and fruity wines with mild tannins, which are designed to be drunk young.