🍷 Pressing (wine)

Pressing is the operation in which harvested grapes or pomace are squeezed to separate the liquid from the solids. For white wine the grapes are pressed at once, before fermentation; for red wine afterwards, when the wine has already taken colour and tannins from the skins. A wine press is used for this.

The OIV names two aims of pressing. The first is to obtain must for grape juice or for fermentation without grape solids. The second is to separate press wine from the pomace after fermentation on the skins, the way red wines are made.

Before pressing, the juice of crushed grapes can be allowed to drain off by gravity, and the must then contains fewer substances from stems, skins and seeds. The OIV requires pressing as soon as possible after harvest or crushing, slowly and progressively, without shredding the berry tissue and without excessive pressure. The OIV describes this gravity draining as a separate operation.

Pressure noticeably changes the composition of the must. In a study of Sauvignon Blanc, juice obtained at higher pressure (0.8–1.6 MPa) had the most phenolic compounds, because these are concentrated mainly in the skin. For "Crémant" sparkling wine, EU rules cap the yield at no more than 100 litres of must from 150 kg of grapes.

Why it matters to you. Must from the first, lighter pressing is more delicate, while under strong pressure it contains more bitter and astringent substances. That is why limiting the must yield is one of the ways appellation rules and winemakers themselves protect the quality of wine.