What are tannins and how do they influence wine?
Tannins, phenolic compounds that give wine its dryness, structure, and aging capacity, are key in red varieties.
Anyone who has ever left a tea bag to steep for too long, or bitten into a thick-skinned grape, is already familiar with tannins. Their name comes from the leather tanning process, and they are one of the hundreds of phenolic compounds found in wine, chocolate, and tea.
Scientists have been studying tannins and other polyphenols in wine for at least a century, but they are only beginning to understand how the brain interprets bitterness, one of the five tastes perceived by the tongue, and astringency, a gustatory sensation linked to memory and experience. Sommeliers have observed that different cultures perceive tannic intensity differently, perhaps due to the abundance of bitter and astringent foods in their regional cuisines.
Growing up on rhubarb and strong tea, rather than mashed potatoes and milk, might influence how you perceive an Italian Barolo with tannins.
The tannins in grapes, called condensed tannins, are found mainly in the skin, pulp, and stems. The longer the must remains in contact with the skins during fermentation, the more tannins are incorporated into the liquid. This is why red wine has more tannins than white wine, which typically separates from the skins before or during fermentation.
Oak also contributes tannins, known as hydrolysates. During aging, the wood expands and contracts with temperature changes, transferring tannins, esters, and polymers to the wine, resulting in distinct flavors depending on its origin, such as France, Spain, Hungary, or the United States. To save time and money, powdered tannin, of natural origin, or oak chips are sometimes added to accelerate absorption. While it may seem like a trick, it's a perfectly acceptable practice.
The winemaker regulates the tannin content by adjusting the contact time with the skins, the amount of rind present, and the decision to ferment whole clusters or filter the solids. Thick-skinned grapes, such as Cabernet Sauvignon or Malbec, have more tannins than thin-skinned varieties, such as Pinot Noir or Gamay. With aging, the tannins bind together in longer chains, softening their bitterness and giving the wine a velvety texture.
When reading labels, tannins are described as light, powdery, velvety, silky, or oaky. Some sommeliers claim to distinguish between grape and oak tannins based on the area of the mouth that feels dry. Furthermore, tannins act as a natural preservative and bind to proteins, so full-bodied red wines pair well with fatty steaks, as they cleanse the palate.