by Charl Theron -
Skin contact is a basic requirement during red winemaking, unless other techniques like thermovinification are used to extract colour from the skins. Different factors like the duration of skin contact, cultivar, fermentation temperature and the ways in which skin contact is applied, play an important role in the result that is eventually obtained.
During red wine fermentation the formed carbon dioxide carries the skins to the surface of the container. This is known as the cap and the management of it will determine the extraction of the colour and tannins from the skins, which will eventually determine the colour and taste of the wine. The correct management of the cap will also influence the potential development of detrimental micro-organisms, determine an equal temperature in the cap and fermenting juice, promote the alcoholic fermentation by the addition of air (oxygen) and prevent the drying out of the skins.
The handling of grapes after destemming plays an important role in the onset of alcoholic fermentation. Vigorous crushing will cause the extraction of more astringent and bitter tannins, because the concentration of insoluble solids is increased by it. Extraction methods causing the damage or breaking of the seeds, must also be prevented. Minimal crushing of the berries prolongs the alcoholic fermentation, decreases phenolic extraction and also increases the fruity flavours of the wine. The volatile flavour compounds in the fermenting juice can also be lost at higher temperatures, because they are removed by the formed carbon dioxide and volatilise more at higher fermentation temperatures. In the case of whole bunch fermentations, some of the flavours are retained in the unbroken berries and only released into the wine after the vigorous fermentation.
The management of skin fermentation during red winemaking differs between red cultivars and techniques like pumpovers, punch-downs or cold soaking are consequently applied differently. In case of Pinot noir, grapes are only destemmed or whole bunch fermentation is used. Although the same principles are sometimes applied with Cabernet Sauvignon, berries are sometimes only broken by loose crusher rollers. The application of cold soaking is also an important principle decision, which needs to be made for red winemaking. It comprises the cooling of crushed grapes or bunches to such a temperature that the onset of alcoholic fermentation is delayed. The initial colour and flavour extraction from the grapes is consequently in an alcohol-free medium and coarse tannins, bitterness or excessive astringency are prevented. Tannins are then eventually only extracted afterwards by the formed alcohol. If spontaneous alcoholic fermentation is also preferred, cold soaking will create an opportunity for such yeasts to initiate the fermentation. In case of Pinot noir, cold soaking is advantageous if it is maintained at 10°C for four to five days. In order to limit spoilage organisms and excessive oxidation in open fermenters during cold soaking, the surface of the fermenters can be covered with a plastic sheet over the cap and a sulphur dioxide solution and dry ice can be used twice daily to exclude air. During cold soaking the cap must not be punched down more than twice daily. In case of Cabernet Sauvignon and Merlot, where colour extraction is usually sufficient, cold soaking is applied for a shorter period …