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.
Mixing the juice and skins during alcoholic fermentation can be done by pumpovers or punch-downs. In both cases it must always be ensured that the cap is properly wet. Punch-downs can be done with different equipment by breaking the cap and submerging the skins under the fermenting juice. There are many types of manual punch-down tools, but cellars also use pneumatic designs sometimes. It can be moved on a conveyor rail to different containers. Punch-downs work best with open fermenters or small fermenters with large lids. Punch-downs are also seen as a gentler form of extraction and consequently preferred for more delicate wines like Pinot noir. The frequency of punch-downs during the peak of alcoholic fermentations depends on the punch-down equipment, but is usually not more than four times daily. In the case of pumpovers, the wine is removed from the fermenter through a bottom racking valve and circulated over the cap to wet the skins. Different spraying methods can be used to wet the cap and sometimes fermenters, equipped with automated pumpover systems, are used to save time and labour. A more oxidative pumpover technique is the so-called rack and return method, where all the liquid is removed underneath the cap to another container from where it is sprayed over the cap to cover the fermenting juice. In some cases of the latter technique, the seeds can be removed from the tank bottom after all the juice has been removed.
Aeration plays an important role during red wine fermentation to polymerise and soften tannins, to stabilise colour and supply oxygen to the yeasts for a sound fermentation. In case of pumpovers, a venture design can for example be used at the delivery side of the hose. Aeration should however be limited when only 5°Balling still need to be fermented.
Apart from temperature and Balling readings during alcoholic fermentation, it is important to taste the fermenting juice regularly to monitor the colour and astringency of it. It is also applicable if wine is left on the skins for further maceration after fermentation, which is sometimes done with Pinot noir.
Higher temperatures do not only accelerate the fermentation rate, but also increase the extraction of colour and tannins. If moderate extraction is required, the fermentation temperatures must be lower, which will also prolong the duration of fermentation (Cohen, 2015).
Cohen, Remi, 2015. Cap management during fermentation. Vineyard & Winery Management, September/October 2015: 31 – 35.