Red wine is made from red grapes, fairly obviously one might think, but in fact some red wines have white grapes added before the process of vinification (or wine making).
The majority of red grapes have clear juice, so all the colour in the wine comes from the skin. The skin also imparts flavours and tannin (astringent compounds). The wine maker will decide how long the skin should be in contact with the juice; the less contact the lighter the wine, the more contact the more full-bodied.
Pressing and primary fermentation
After the grapes are picked and the stems and any foliage is removed. The juice and skins are first stored in fermentation tanks. The skins rise to the top of the liquid so are occasionally stirred through to increase the tannin levels. This initial fermentation process is then brought to an end by reducing the temperature of the wine to near freezing. This process also allows for the removal tartrate crystals which form during this first fermentation.
Next, the wine is fermented for a second time at a much slower and more controlled pace, this time in an airtight vessel – usually a large tank or sometimes oak barrels. The vessel must be airtight to prevent the wine from becoming oxidised. This process includes the conversion of the tart-tasting malic acid present in the grape juice into milder tasting lactic acid, known as malolactic fermentation.
Maturation and oaking
Some wines, usually red or sparkling, are left to mature in the bottle in a process known as bottle conditioning. This is especially the case with wines that are meant to be left for many years and drunk at a later date. The producers may decide to store the wine themselves if they have the right facilities such as a cellar and then release the wine when it is ready to be consumed.
Most wine is matured in large stainless steel tanks, although some wine makers still use wooden barrels. These are usually made from oak which can impart flavour into the wine – generally oak barrels will impart flavour only for the first two or three years of use. As the oak flavour is valued in some wines, wine makers who use steel vats will often use a string bag filled with oak chips to impart the flavour.
The amount of time in oak is down to the style of wine the winemaker is aiming for – from slightly oaked to heavily oaked – but wine can spend up to three years in barrels and sometimes more.
Oak gives the wine more complexity in terms of flavour and tannin. Another benefit is the greater capacity for the wine to age, with some wines not reaching their optimum drinking time for many years.