As the alcoholic fermentation proceeds, ethanol is produced and the temperature rises; both these activities participate in the dissolving of phenolic constituents. Ideally, only those grape components contributing positively to wine flavour and aroma should be dissolved. It is vital for the winemaker to have a clear idea of the state of maturity of his fruit as the quality of extracted substances is directly proportional to fruit quality.

The fruit quality and desired wine style will determine the extent of phenolic extraction required:

• The level of extraction of phenolics from poorer quality grapes is normally reduced so as not to extract too many bitter and herbaceous aromas.
• Light, easy (early) drinking reds are usually made with shorter skin contact times (around 8 days) and can be made with lower quality grapes.
• Full-bodied reds intended for ageing are usually made with longer skin contact times (3 weeks) and require a riper, better quality vintage.
• With high quality vintages, extended skin contact periods (1 month or more) may lead to a softening of the tannins due to polymerisation.

Commercially-available macerating enzymes can be used to increase the extraction of colour and tannins during the skin contact process. In general, the anthocyanins are extracted first, in the low alcohol stage of fermentation. The higher alcohol and temperature levels of later fermentation favour more tannin dissolution. However, tannins extraction is also important for colour as tannin-anthocyanin polymers are more stable.