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Just over a century ago, wine was still produced with grape stems, simply because there was no process in place to separate the grapes from the woody vegetative structure of the cluster. France was the first country to develop a machine for destemming grapes. This invention led to one of the first decisions made by winemakers in the vinification of white wine: should whole clusters or destemmed grapes be pressed ? As harvest approaches, in addition to monitoring the technological and phenolic ripeness of the grapes, it is now essential to pay special attention to the condition of the stems: if they are well lignified, the stems will enhance the wine with aromas and complexity, but if they are too green, beware of the herbaceous aromas and astringent tannins they may impart.
Direct pressing of whole clusters
Generally, it is advisable to use this technique in vintages with low acidity, as it helps impart vibrancy and freshness to the wines. During pressing, the stems shield the grape berries from excessive pressure: fewer berries are destroyed, and less undesirable bitter tannins reach the must, resulting in a purer and fruitier juice. The spaces created within the clusters by the stems act as drainage channels inside the press, significantly improving pressing efficiency. The resulting musts are less cloudy, allowing for gentler clarification. In the case of direct pressing, the second fraction is typically more appreciated for its phenolic balance and ageing potential. However, it also slightly reduces alcohol content and dry extract.
This method is also used to press the grapes for Champagne production: the red grapes remain almost colorless and the white varieties maintain their highly prized elegance and acidity, to such an extent that it has become mandatory in this region. The result is wines that, upon tasting, exhibit fresh balsamic and herbaceous notes of great freshness. In general, this type of pressing, by aiding in achieving better acidity levels, enhances the ageing potential of the wines. However, if the stems are not ripe, they risk adding a certain roughness to the tannins and aggressive vegetal notes.
Pressing of destemmed grapes
Destemming is crucial when the stems are not sufficiently ripe or when the grapes have been damaged by dehydration or disease. If the stem is not adequately lignified, it can impart a herbaceous aroma, and its water content can also reduce the wine’s alcohol content. When we press the grapes after destemming, the mass that forms inside the press becomes more compact, requiring more frequent rotation of the press dum during the process. This results in cloudier musts, needing more aggressive clarification. Although modern destemming machines are highly efficient, the process can oxidize the must, and there is a risk of breaking the stems or seeds, giving the juice a certain woody or herbaceous taste.On the other hand, managing destemmed grapes allows for better temperature control during the process, as the stems have the ability of absorbing heat.
There is no better method than the other; the choice should be made based on the vintage circumstances, climatic conditions, ripeness, and the desired wine style. Either method has the potential to produce exceptional wines, but as it is often the case in winemaking, the final outcome is determined in the vineyard, as the grapes’ condition will dictate the path to follow.
