Some thoughts on tannins in wine
posted 8th March 2023
Tannins are polyphenols, the primary source in wine being the skins of the grapes. Stalks also contain tannins of a greener, harder nature and nowadays are, with some notable exceptions, generally excluded from the winemaking process. Oak is another source of tannin, and wines matured in new or young barrels, or otherwise oaked, will absorb tannin from the wood.
Tannin is mostly detected by tactile sensations, particularly making the teeth and gums feel dry, furry and gritty. The sensations can be mouth puckering, and after tasting wines high in tannin, you want to run your tongue across the teeth to clean them. Hard, unripe tannins also taste bitter and 'green'. Tannin is a key component of the structure of classic red wines and gives 'grip' and solidity.
Tannin binds and precipitates protein. This is one of the reasons why most red wines match red meats and cheeses successfully. This combination causes wines containing tannin to congeal into strings or chains as it combines with protein in the mouth, and thus our perception of tannin in wine will change if we keep it in the mouth too long. To observe this, take a good mouthful of red wine low in tannin such as a Beaujolais, chew it for 20 seconds or so and then spit out into a white bowl. Now, repeat the exercise with a red wine high in tannin such as a Barolo. It will be observed that the greater the tannin level in the wine, the more the wine will have formed these strings.
Novice tasters often confuse the sensations of acidity and tannin. A classic traditionally made Barolo, which is high in both, is a good example to taste to distinguish between them. The tannin gives the dry, astringent sensations on the teeth, gums, and even hard palate. The acidity produces the tingling sensations on the sides of the tongue and cheeks.
With maturation and ageing, tannins will be precipitated, and will form a sediment in the bottle, or glass if the wine has been carelessly handled at service.
It is often written that white wines contain no tannin. This is not true, although generally, the levels are low compared with red wines. The grapes for white wines are pressed pre-fermentation, the solids are settled or the must otherwise clarified, and reasonably clear juice is fermented. Unless there is any period of skin contact (macération pelliculaire), post-crusher and pre-press, the phenolics in the skins will have limited impact. In the case of whole cluster pressing the presence of grape phenols is minimal. White wines that have been fermented or matured in oak barrels (or otherwise oaked) may contain significant oak tannins.
The quantity of tannins in white wines ranges from 40 to 1300 mg/l, with an average of 360 mg/l. Red wines contain from 190 to 3900 mg/l, with an average of 2000 mg/l. Thus, it will be seen that whilst the average tannin level of red wines is six times that of whites, many white wines contain considerably more tannins than some reds. Grape tannin, usually in powder form, may be added during the fermentation process, to give an over-soft red a little more 'grip'. Grape tannin is an authorised oenological product in the OIV CODEX and its addition is legal in most countries worldwide, including member states of the EU.
When undertaking a comprehensive, structured tasting, wine tannins should be assessed and noted for both level and nature. We may assess the level on a scale that runs from low, to high. The nature of the tannins may be described as ripe/soft or conversely unripe/green/stalky. The texture of the tannins should also be noted. Tannins that are assertive, rough, and very gritty may be described as coarse, whilst those with a smooth, velvety texture as fine-grained. Wines with high or very high levels of tannins are coarse-textured. Those with very unripe tannins may be considered to be flawed.