Maceration (wine)

Maceration is the winemaking process where the phenolic materials of the grape—tannins, coloring agents (anthocyanins) and flavor compounds—are leached from the grape skins, seeds and stems into the must.

In the production of white wines, maceration is either avoided or allowed only in very limited manner in the form of a short amount of skin contact with the juice prior to pressing.

[1] While maceration is a technique usually associated with wine, it is used with other drinks, such as Lambic, piołunówka, Campari and crème de cassis, and also used to steep unflavored spirit with herbs for making herb-based alcohol like absinthe.

The process of maceration begins, to varying extent, as soon as the grapes' skins are broken and exposed to some degree of heat.

[1] An efficient and modern method of maceration is the "pneumatage process" in which compressed air or gas is sequentially injected into the juice.

Cabernet Sauvignon musts interact with the skins during fermentation to add color, tannins and flavor to the wine.
Most red wine grapes have their color concentrated in the skin, while the juice is much lighter in color. The duration of contact between the crushed grape skins and their juice impacts the final color and flavor profile.
The "cap" of grape skins being "punched down" to maximize maceration.
An example of the difference between a red fleshed teinturier grape ( Agria left ) and a red wine grape variety with its skin peeled off to show that its flesh and juice is naturally white ( Grenache right ). The vast majority of red wine grapes are like the Grenache on the right with the red color of wine coming from skin contact during winemaking.