Maceration is the winemaking process where the phenolic elements of the grape; tannins, colouring agents (anthocyanins) aroma and flavour compounds are released ideally from the grape skins. Maceration is the process by which red wine achieves its red colour, since 99% of all grape juice is a clear colour. When making white wine, maceration is either avoided or only performed for a very short period of time. This is can be seen in the wine production of varietals with less natural flavour and structure like Sauvignon Blanc.
For Rosé production, red wines grapes are allowed some maceration time between the skins and juice, but not to the extent of red wine production. The process of maceration begins as soon as the grape skins are broken and exposed to a degree of heat.

 

Temperature is a key influencing control; with higher temperatures encouraging more breakdown and extraction of the phenols from the skins and other grape elements.
Cold maceration is a practice of cold soaking the skins of red grapes in their juice for a period of time prior to the start of fermentation. Temperatures of the must are kept low to encourage extraction by water and added sulphur dioxide rather than relying on heat and alcohol to act as a solvent.
Maceration continues during the fermentation period, and can last well past the point when the yeast has converted all the sugars to alcohol. During fermentation, higher alcohol levels can encourage this process with the alcohol acting as a solvent to assist in the breakdown of the compounds within the grape components. This process seems to slow, until the wine reaches an alcohol level of 10%.
Depending on the grape varietal, the process of maceration can enhance the body and mouth-feel for many wines. Greater extraction can add to the complexity and life expectancy of the wine by developing more complex tannins that will soften over a longer period of time. Care must be taken as too much extraction can also increase the harshness of some tannins to where the wine is not very approachable or worse, out of balance.