Dr. David Muhleman

The-Wine-Educator    WINE & SPIRITS EDUCATION AND CONSULTING SERVICES FOR THE CONSUMER AND THE PROFESSIONAL

Tannins

In order to understand the chemistry of wine, you must first understand that the basic building block for much of wine chemistry centers on the organic molecule called a “phenol.” In chemistry terms, “phenols” are a circular molecule of carbon and oxygen. That said, think of phenols as the basic building block upon which other phenol molecules (poly phenols) or other organic molecules are added to make larger molecules. Each one of these larger molecules interacts with other (organic and inorganic) molecules to produce other molecules to include acids, esters, aldehydes, and a whole range of the chemicals that make wine what it is. You can think of these molecules as the chemical components that make up wine. Remember, 80% of wine is hydrogen and oxygen molecules combined: H2O.

Tannins are astringent, bitter plant polyphenols that either break up or shrink proteins. The key words being “bitter,” “plant,” “polyphenols” that attack proteins. Our mouths are full of protein, so when you put a bitter, polyphenol, from a plant in your mouth, a chemical reaction takes place and the astringency from the tannins causes the dry and puckery feeling in the mouth.

The term tannin comes from the use of tannins (often tannic acid) in tanning animal hides into leather, where the polyphenols attack the proteins in the animal hides. One of the plants that contain these tannins are grapes (primarily in the stems, seeds, and skins) so when you use the stems, seeds, or skins to make wine (particularly red wine) the tannin molecules transfer into the wine.  If the winemaker were to use the skins, seeds, and stems in white wine, you would have tannic white wines.

Tannins differ depending on the source. Tannins in grape skins and seeds (the latter being especially harsh) tend to be more noticeable in the finish wine. The stems of the grape bunches also contain tannins, and will contribute tannins if the bunches are not de-stemmed before pressing and/or fermentation. Tannins can also come from the wooden barrels the wine is fermented/aged in.

Modern winemakers take great care to minimize undesirable tannins from seeds by crushing grapes gently when extracting their juice, to avoid crushing the seeds. Pressing the grapes further results in wine which is more tannic and might be kept separately. De-stemming is also widely practiced. Wines can also take on tannins if matured in oak or wood casks with high tannin content.

So why are these astringent, bitter, polyphenols good for wine?

Tannins play an important role in preventing oxidation in aging wine. Tannins allow a wine to age and mature, without turning “bad” (oxidized).

Tannins have the effect of making wine difficult to drink compared to a wine with a lower level of tannins. Tannins often leave a dry and puckered feeling in the mouth that is particularly profound when drinking tannic wines without the benefit of food. As tannic wines age, the tannins begin to decompose and the wine mellows and improves with age, helping the wine survive for as long as 40 years or more.

Wines that are vinified to be drunk young typically have lower tannin levels. The point being, that tannins are a choice. They are a choice of the wine maker and the wine drinker. Some would say tannins are good for the wine; other would say tannins are bad for the wine. It depends on what you want out of the wine.

The chemistry of tannins is relatively simple; they are these polyphenol molecules that change the structure of wine. But whether you want that changed “structure” in your wine, is in the personalized taste of the wine consumer.