Due to the presence of skins during fermentation, red grapes have several unique processes that winemakers need to make sure to consider to ensure successful fermentation.
Also referred to as cold maceration, the practice of cold soaking grapes has become more prevalent in the modern wine industry. After processing into the winery, the must is not inoculated. Depending on the winery's program, this may be a few days to upwards of two weeks. The aim of cold soaking is to allow the extraction of water-soluble color and flavor compounds without harsher phenolic compounds like tannins, which are significantly more soluble in the presence of alcohol.
Cold soaking proponents contend the resulting finished wines increase color, fruitiness, flavor intensity, and mouthfeel with lower astringency and bitterness. Another major benefit of cold soaking must is more accurate chemical analysis prior to fermentation onset as the juice 'soaks up' for sugar and acid from the skins.
The main requirements for successful cold soaking are pretty simple.
A 'fermentation cap' is created when CO2 produced by the yeast pushes the grape skins to the surface of the tank. The cap can pose some problems if it is not managed properly.
Different cap management regimes have a different effect on extraction of skin and seed components. Choosing the right method depends on fermentation vessels, wine style, and time constraints. Cap management programs will often combine method.
Winemaking additives are in no way exclusive to red varieties or considered necessary during winemaking activities. All but one (non-ellagic tannins) of the additives discussed below are naturally occurring in grapes and/or wine at some levels. Separate articles discuss fermentation nutrients and wine additives in depth.