Tannin

Science  ·  Beginner  ·  3 min read

Tannin is a class of phenolic compounds found in grape skins, seeds and stems, and in oak barrels. Tannins create the astringent, drying, sometimes bitter sensation in red wine, and they are the principal structural component of reds. In white wine, tannins are usually very low, although barrel-aged Chardonnays can pick up some oak tannin. The cool UK climate generally produces moderate tannin levels, with English Pinot Noir showing a soft, fine-grained structure.

What tannin does

Tannin binds to proteins in saliva, which is why it feels drying in the mouth. The sensation is not flavour in the traditional sense, but it has a huge impact on the texture and the perception of a wine. A high-tannin wine feels firm, structured and grippy. A low-tannin wine feels soft, round and approachable.

Tannin also reacts with colour pigments to stabilise the colour of a red wine, and it reacts with oxygen to soften over time. A young, tannic red often needs years of bottle ageing to become approachable. As the wine ages, the tannins polymerise into longer chains, which feel softer on the palate even though the underlying compounds are still there.

Sources of tannin

There are three main sources. Skin tannin comes from the contact between the juice and the grape skins during fermentation. The longer the contact, the more tannin is extracted. Seed tannin comes from the seeds, which can release harsh tannins if they are crushed during the fermentation. Oak tannin comes from the barrel, particularly new oak, and adds a different kind of structure, often described as vanilla or spice.

UK winemakers manage tannin by controlling the fermentation. Cold soaks before fermentation can extract colour without tannin. Gentle punch-downs or pump-overs, rather than aggressive ones, can limit seed tannin extraction. Pressing decisions affect how much tannin ends up in the wine. The result is a tannin profile that is shaped by the winemaker's intent.

Tannin in English wines

English Pinot Noir is naturally moderate in tannin, because the thin skins of the variety do not release a lot of phenolics, and the cool climate limits tannin polymerisation during ripening. The wines are typically soft, fine-grained and approachable young, with a tannin profile closer to red Burgundy than to a Cabernet Sauvignon from a warm climate.

English red wines from hybrid varieties, including Regent and Rondo, tend to have higher tannin because the grapes have thicker skins and more phenolic content. The wines are deeper in colour and more structured, and they often benefit from a few years of bottle ageing. The English red wine category as a whole is still small, but the quality is rising fast.

Tannin and ageing

Tannin is the engine of red wine ageing. A high-tannin red, well-made and well-cellared, can age for decades, with the tannin gradually polymerising and the wine developing tertiary aromas of leather, tobacco, mushroom, forest floor and dried fruit. A low-tannin red, by contrast, will not age as long because the structure is not there to support the slow chemical changes.

For English red wines, the ageing potential is still being explored. The first commercial plantings, from the 1980s and 1990s, are now reaching 25 to 40 years of age, and the early examples are drinking beautifully. The future is bright for the category.