Red Wine Production
Ribereau-Gayon (1998) states that:
“Red wine is a macerated wine. The extraction of solids from grape clusters (specifically from skins, seeds and possibly stems) accompanies the alcoholic fermentation of the juice. The length and intensity of maceration are adjusted according to grape variety and the type of wine desired.”
It is the presence of skin contact in the alcoholic phase (and the colour of the grape) that distinguishes red winemaking from white winemaking. Skin contact leads to the extraction of phenolic compounds from the grape skins into the must, and thus, into the wine. Phenolic compounds (also called polyphenolics or polyphenols) are a very large group of compounds based on the phenol molecule.
Two main types exist:
- Non-flavonoids, simpler phenolics such as benzoic and cinnamic acid and derivatives.
- Flavonoids, which include substances such as catechins, resveratrol, and anthocyanins.
Anthocyanins are the red pigments found in the skin cells that produce the red colour in red wines. Tannins are polymerised catechin molecules that produce the astringency in wines which gives the wines ‘mouth-feel’ or ‘structure’. Roughly speaking, the smaller the tannin, the more bitter it is, but if they become too large, they stop being dissolved in wine and form a precipitate at the bottom of the bottle.
Anthocyanins can react with tannins and form more stable colour compounds in young wines. Over time (months and years!) these compounds polymerise (join together) further and precipitate out.
The quality and characteristics of the phenolic compounds in the vintage vary according to the grape variety and its maturity.
Some phenolics may be; highly coloured, stable, soft, full. Others may be; herbaceous, bitter, astringent. Much of the art of red winemaking is in controlling the extraction and development of grape phenolics.
Red winemaking can be broken down into 4 main steps:
- Pre-fermentation processing: de-stemming and crushing
- The alcoholic fermentation with skin contact and phenolic extraction
- Draining and pressing
- The malo-lactic fermentation (MLF)