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If the aromas and flavours of a wine are best likened to a painting, then tannins are more akin to sculpture. Unlike the former, more ethereal and distant, tannins have a tactile, physical presence that brings a sense of closeness. This is why they are often described as having a three-dimensional quality.

Depending on the wine, tannins may be described as ‘rounded,’ ‘angular,’ or ‘robust.’ They can also be ‘grippy,’ ‘soft,’ or even ‘velvety.’

Each of these terms points to a sense of volume and texture - much like a sculpture. But what exactly are tannins, and how do they shape the sensory landscape of a wine?

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What Are Tannins?

Tannins are natural compounds found in tea, coffee, cocoa, nuts, and even blueberries. In fact, these polyphenolic compounds are present in virtually all plant species.

The word’s etymology traces back to the Latin term ‘tannum,’ referring to crushed oak bark traditionally used in leather tanning.

In wine, tannins come primarily from the skins, seeds, and stems of grapes. They are also imparted by oak barrels where many wines age.

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What Is the Role of Tannins?

Among their many roles, tannins help protect plants from pests and diseases.

To ensure effective seed dispersal, the astringency of tannins also deters birds from eating fruit before it has fully ripened.

Here, ‘astringency’ is the key word. Also with Latin roots, it refers to something that ‘tightens’ or ‘contracts.’

This ‘tightening’ sensation on the palate is the dry, firm grip that immediately discourages us from eating unripe fruit. Yet, what could be a negative sensation has been artfully shaped over millennia to enhance the pleasure of enjoying a fine wine.

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How Do Tannins Shape the Tasting Experience?

This enhancement of pleasure is conveyed in multiple ways. Much like marble in a classical sculpture, tannins provide the structural foundation upon which the art of wine reveals itself to the senses.

Beyond this foundation, tannins also add cohesion and texture to wine: the ‘marble’ can be sculpted into smoother surfaces, as found in softer wines, or into rougher, more intricate contours, as seen in more tannic wines.

Together with acidity, sweetness, and alcohol, tannins contribute to the style and balance among various elements.

For instance, the firmness of tannins is typically heightened in wines with sharper acidity; conversely, higher sweetness can counterbalance the roughness of firmer tannins, adding smoothness to the wine.

Finally, in synergy with a higher alcohol content, tannins tend to amplify the sense of body and volume in wine. Wines with greater levels of tannins and alcohol thus feel fuller and more opulent.

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What Role Do Tannins Play in Wine Aging?

As wine ages, tannins gradually bond together to form larger molecules. This process, known as ‘polymerisation,’ results in aged wines becoming smoother and less astringent.

The interaction between tannins and oxygen also plays a crucial role in developing the aromas, flavours, and textures as the wine matures.

But tannins serve additional purposes, as they help stabilise the wine's colour during fermentation and aging. Acting as natural preservatives, tannins contribute to a wine’s longevity.

In fact, alongside acidity, tannins are one of the most significant factors in determining a wine’s ageing potential. So much so that, in 18th-century France, winemakers and merchants used the taste of tannins to assess a wine’s quality and aging prospects.

Interestingly, this rudimentary ‘tannin test’ led some less scrupulous merchants to add oak shavings—and even tree bark—to artificially boost tannin levels, underscoring the value placed on tannins as markers of quality.

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How Do Tannins Vary in Wines?

In the vineyard, tannin levels vary according to grape variety, terroir, and growing conditions.

As expected, different grape varieties have different tannin concentrations. Varieties like Baga or Touriga Nacional are known for their high tannin levels, unlike varieties such as Arinto or Fernão Pires.

This is unsurprising, as red wine grapes are particularly rich in tannins due to their prolonged contact with grape skins during fermentation.

However, even within the same variety, grapes from cooler regions tend to produce more intense, angular tannins, whereas those from warmer climates often yield softer, rounder tannins.

Tannin concentration also depends on the ripeness of the grapes at harvest—riper grapes generally have lower tannin levels.

Conversely, tannins are usually more abundant in grapes grown at higher altitudes or lower latitudes. In these cases, the high solar exposure leads the grapes to protect themselves with additional tannins.

And, of course, winemakers sculpt the tannin structure to suit their stylistic goals. This structure can be shaped through various techniques, such as fermenting with stems, extended maceration, aging in oak, micro-oxygenation, or careful temperature management.

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How Can We Appreciate the Tannins in a Wine?

Tannins are fundamental in defining a wine’s character, origin, and sensory aesthetic.

For example, historically, Dão wines have been distinguished by their fine, elegant, and well-structured tannins, as seen in wines like Quinta da Alameda Parcelas.

Douro wines, on the other hand, are prized for their robustness and concentration, while wines from the Alentejo are known for their ripe, rounded tannins.

When appreciating any of these, think of tannins as more connected to a wine’s texture and structure than to its flavours and aromas. And imagine all these different elements as interconnected parts of an artistic experience.

After all, wine is, indeed, a form of art.