What are Tannins?

What are Tannins?

Defining tannins can be tricky even for seasoned wine enthusiasts. According to the dictionary, tannin is a yellowish or brownish bitter-tasting organic substance found in various plant tissues, commonly used in leather production and ink manufacture.

Tannins in Wine

Wine enthusiasts often ponder the nature of tannins. Recently, someone asked me about their evolution in aged red wines. I likened tannins to the Rolling Stones—just when you expect them to mellow and fade, they return with vigor, commanding attention and dancing on your palate.

Tannin Fundamentals

Only wines fermented with seeds and skins will be tannic, and all red wines have tannin. Tannins contribute to the color, structure, and flavor of wine, responsible for the drying sensation, red color, and some dark fruit flavors.

Tannins Over Time

I am reminded of the staying power of tannins whenever I taste red wines, irrespective of their age. Young red wines are predictably tannic. But even in wines held for a decade in a wine cellar, tannins rarely melt away like butter.

The Bitter Truth

Bitterness is not universally beloved. About 20% of people are genetically predisposed to find high levels of tannin distasteful. This evolutionary trait helped ancient hunter-gatherers avoid poisonous plants, a survival advantage still present today.

Color Versus Tannins

Tannin levels vary by varietal, and even lighter-colored wines can be quite tannic if high in acidity or alcohol.

Oak’s Influence

Tannins are also leached into wine from oak; the newer the barrels, the stronger the presence in mouthfeel and flavor.

Managing Tannins

The major threat tannins pose is bitterness or astringency. That’s why so much attention is paid to tannin management, starting in the vineyard and extending through fermentation. Harvest dates are crucial. Picking underripe grapes gives tannins a green, herbal edge; overripe grapes can taste raisiny or pruney. Winemakers now taste and chew grape skins and seeds to assess ripeness and tannin levels.

Fermentation Influence

Fermentation methods impact tannin strength, with some winemakers opting for shorter fermentations to extract color and flavor, while others prefer extended vinification to soften tannins. Some even use tannin powder to enhance their wines.

Tannins and Aging

Because tannins act as a preservative, they are one of the most important factors in determining the longevity of red wines. Their enduring presence is a revelation that comes from drinking older red wines, great or otherwise.

The Balance Factor

When you taste a mature wine that has evolved gracefully and maintained a mix of youthful flavors while developing subtle nuances, you can be assured that it began life in near-perfect balance. That’s why winemakers ultimately define great wines by their balance. Foremost among the factors determining balance are the structure and amount of tannins.

Additional Considerations

Concentration, richness, acidity, and alcohol (and sugar in sweet wines) also play vital roles in a wine’s age-worthiness. Moreover, defining what constitutes a mature wine differs for each of us.

Century-Old Wines

The last time I tried a pair of 1870 Bordeaux, from Châteaus Lafite Rothschild and Latour, both exhibited the faded, wilted rose petal and dried-fruit scents of their age. I admired the longevity of these wines but was amazed by how persistent the tannins remained. Clearly, these wines aged beautifully because of their tannins and balance. More often, older wines dry out and lose their fruit vitality. Then tannins are all that remains. You rarely have to look hard to find tannins. They hang around like the Stones. No one knows when they’ll fade away.

The Science of Red Wine

The science of flavor is still in its infancy. Only a handful of the trace elements of wine have been studied, and many flavor compounds, in different proportions, can give distinctly different flavors.

Condensed Tannins

Research indicates that a class of polyphenols has antioxidant characteristics with potential health benefits. These polyphenol antioxidants may reduce the risk of cardiovascular disease and cancer. High levels of polyphenols can generally be found in fruit skins, with some of the highest percentages in grape, apple, and orange skins. This class of polyphenols, called condensed tannins (anthocyanins), gives red wines their astringency and bitter taste. Tannins are not water-soluble and will precipitate protein, eventually causing the red and bitter stuff in wine to fall to the bottom of the bottle, turning the wine from ruby-red to brick-colored. This is why people age wines. Tannins are also an important ingredient in tanning leather, traditionally sourced from oak bark, though synthetic tanning agents are used today.

Esters and Flavor

The biggest contributor to flavor is yeast. It is the fermentation process that truly gives a wine its flavors. If conditions are right, acids will combine with alcohol or tannin in the grape to form an ester. These are the flavor compounds in wine. When you say a red wine has a berry-like character or smells like roses, it is because the esters in the wine are mimicking the smell of berries. Flavors such as apple and pear can also come from the acids (tartaric and malic) in wine. These esters can work together to create new flavors. For example, ethyl butyrate (from the grape) with diacetyl (malolactic fermentation) yields a butterscotch attribute in a wine. Another example is ß-damascenone, which gives an apple, fruity flavor and will elevate other fruity notes (such as a-ionone) in a wine. Sometimes the esters will clash: a high concentration of methionol will blunt most fruit flavors.

Polyphenols

One of the most important flavor elements in wine, especially red wine, polyphenols, translates to “many phenols” or, more prosaically, “lots of aromatic stuff jammed together”. They are also responsible for the coloring of some plants—for example, the color of leaves in the autumn and the skin color of red wine grapes.