🍷 Pomace

In the cellar, pomace starts as crushed grapes: juice together with the skins, seeds and sometimes stems. Red wine begins here, because the must ferments on these solids and takes colour, tannins and aromas from the skins. After pressing, the solids left over are the pomace in the narrow sense. ¹²

What maceration is. The International Organisation of Vine and Wine defines maceration as leaving the solid and liquid parts of the grapes in contact for a shorter or longer time, before, during or after fermentation. The aim is to dissolve substances from the grapes, notably phenolic compounds, aromas and their precursors. ¹

The classic red wine method. After crushing and optional destemming, the solids and the juice are left together, and maceration and fermentation run at the same time. To extract skin substances faster, winemakers pump over, irrigate the cap of skins, use self-irrigating tanks or recirculate the wine through the marc. ²

Colour comes from the skins. In most varieties the anthocyanin pigments sit only in the skin and the juice is colourless, so without fermentation on the skins there is no red wine. The exception is varieties with coloured flesh, such as Garnacha Tintorera, whose juice is red straight away. ⁷

Skin and seed tannins. Skin tannins pass into the wine first, and seed tannins later as fermentation goes on. In a Cabernet Sauvignon study, skin tannins peaked by the first sampling, while large seed tannins kept rising for up to 20 days, with astringency and bitterness growing. In industrial tanks tannins increased up to 12.7% alcohol, about 9 days of maceration. ⁵⁶

Cold before fermentation. For red wine the OIV allows prefermentative cold maceration: destemmed or crushed grapes are kept cold before fermentation starts. This releases more skin compounds, adds aromatic and taste complexity and improves colour. Grape health and ripeness must be checked, oxidation and spoilage prevented, and the length matched to the wine style. ³

Heat before fermentation. Another option is to heat whole, crushed or destemmed grapes before fermentation to extract colour faster and more fully and to stop enzymes. The heating must neither concentrate nor dilute the must, so excess heat is avoided and heating by steam injection is forbidden. ⁴

Pressing and pomace. When fermentation on the skins is over, the wine is drawn off and the solids are pressed; what remains is pomace. EU rules forbid over-pressing, which squeezes too much out of the grapes. ²⁸ The OIV also lists cold maceration for white wines and the maceration of raisined grapes or their pomace in wine. ¹

Why it matters to you. Red wine is wine fermented on its skins: the longer the contact, the more colour and tannin, but long contact with the seeds makes wine more astringent and bitter. ⁵⁶ What happens to the pressed pomace afterwards is covered on the «Pomace» page.