VINEYARD AND CELLAR UPDATE

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.

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Skin fermentation during red winemaking.

Red wine fermenter with automatic pumpovers. Epoxy coated open concrete fermenters with cooling plates for punch-downs.

 

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).

Reference

Cohen, Remi, 2015. Cap management during fermentation. Vineyard & Winery Management, September/October 2015: 31 – 35.

www.vwmmedia.com.

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