The role of tannins in wine: Masters of Wine explain (2024)

Tannins are easy to detect in young red wines – their presence creates a drying sensation on the tongue and the inside of the cheeks – but how this complex group of chemical compounds behave in wine as it ages is a conundrum that’s still baffling scientists. Found in grape skins, seeds and stems, the polyphenols act as the skeleton within a wine, holding everything together.

While further research is required in order to fully get to grips with how these compounds evolve in wine over time, vintners are acutely aware of the impact of tannin quality on the final product, and the steps that need to be taken both in the vineyard and the winery to ensure their tannins are adequately developed and properly managed, so as to not throw a wine’s balance off kilter.

Nature’s defence

Tannins are polyphenolic compounds that bind to and precipitate proteins. In plants tannins are primarily used as a defence against pests. When released from the plant, they react with proteins in saliva to create a drying sensation in the mouth and an unpleasant astringent taste to deter animals from eating them.

There are two types of tannins – flavonoid tannins and non-flavonoid tannins. The former are composed of single tannin molecules that bind together to form bigger macromolecules called polymers in a process called polymerization. These tannins define a wine’s mouthfeel and astringency level. Non-flavonoid tannins, meanwhile, are a type of phenolic acid found in grape flesh that contributes to the texture of wine. These tannins can also be found in coffee, black tea and beer.

All red wines contain tannins due to extended contact with the must containing these polyphenol molecules during the production process. White wines and rosés, conversely, have little to no tannins as they have minimal contact with the grape skins. The term ‘tannin’ takes its name from the tanning process – the practice of using plant extracts to cure leather. When applied to animal hides, tannins bind to and cross-link the proteins, turning soft skins into tough leather.

While the basics may be understood, scientists are still trying to figure out exactly how tannins behave in wine. “The bonds between tannin polymers are repeatedly breaking and reforming in wine in a temporal sequence, making them a hard subject to study,” says wine scientist, Dr. Jamie Goode. “Only now, with highly sophisticated analytical devices, are scientists beginning to get a handle on tannins in wine.”

The long and short of it

Traditional thinking on how tannins behave and evolve in wine as it ages is currently being challenged. “The old myth was that tannin chains get longer and longer until they are too big and heavy to stay in the liquid, so they fall out as sediment, making the wine taste softer by removing a portion of the tannins,” says Master of Wine, Caroline Gilby. “Research has found this to be wrong and it’s short-chain tannins that taste softer, while longer ones taste more astringent. If the myth were true, wine would get more astringent as it aged, as tannins polymerised into longer chains, but that's not what we see happening.”

While it’s largely agreed upon that tannins seem to soften as wine ages, scientists haven’t worked out why yet. “The concept of tannins getting bigger and falling out of wine as a deposit over time isn’t based on good scientific data, and what actually takes place in wine ageing is uncertain,” admits Goode, adding, “It could well be that tannins are breaking up in the acidic environment of the wine and are getting smaller.” Master of Wine and Italian wine specialist, Sarah Heller, admits that the chemistry behind these phenolic compounds is “incredibly complex”, and more research is needed to fully understand how tannins behave.“It’s common to talk about tannins forming longer chains and becoming smoother with time, but at a molecular level, highly polymerised tannins have a higher level of interaction with salivary proteins than shorter chains. It’s really only once they become so large that they precipitate out of the wine that we get this smoothing effect,” says Heller, who believes tannins play a vital role in the fine wine ageing process. “Tannins (which are antioxidants) and pH are the two most important factors that determine a wine’s ageing potential. Research suggests that the impact of tannins on wine longevity depends on both their quantity and quality, though exactly what type of tannins improve ageability and whether they can be detected through tasting is still being worked out.”

How tannins behave in wine as it ages is a conundrum that’s still baffling scientists

Quality over quantity

Speak to any winemaker around the world and they’ll tell you that ‘great wine is made in the vineyard’. The same can be said for tannins, as it all comes down to the quality of the raw material. Wine growers are becoming increasingly aware of the need to nurture high quality tannins in their grapes in order to produce quality wines. Everything from climate and grape variety to sun exposure can impact tannin levels in grapes, with higher altitude vineyards that are exposed to higher levels of ultraviolet light creating grapes with a greater tannin content.For Peter Sisseck, the Danish-born winemaker and owner of revered Spanish wine label Pingus from Ribera del Duero, grape health is the number one factor in determining tannin quality. “You can never go beyond the quality of the vineyard, only detract from it through poor vineyard management and vinification,” says Sisseck, who extracts tannins from grape skins, stalks and seeds, depending on the vintage. He’s increased the finesse in his tannins over the years by fermenting at lower temperatures, performing less pump-overs and working with older and larger oak barrels.

In California, Trester Goetting, chief winemaker at Ridge, believes there’s a “direct correlation” between grape quality and tannin quality. For his top drop, Monte Bello, he only works with grape skin tannins. “Seed and stem tannins tend to be very aggressive with different phenolic compounds than skin tannins,” he says. “So I like to de-stem the grapes and crush the fruit so the berries remain as whole as possible, which allows for more control of the tannin extraction.” Having learnt what works after many years of experimenting, Goetting now tweaks his winemaking regime depending on where his grapes are grown. “The extraction techniques I used to use for valley floor fruit in Napa are completely different to the techniques I now use for higher elevation mountain fruit. The same holds true for extraction techniques of different varieties,” he reveals.

Thick-skinned grapes like Northern Italy’s Nebbiolo have high levels of tannins, while thin-skinned varieties like Pinot Noir contain a much smaller amount. Picking dates are paramount in determining the quality of tannins, as grapes picked too early are at risk of displaying more aggressive and astringent tannins, while those picked in warmer climates with an abundance of sunshine tend to yield wines with softer, riper tannins. For winemakers in warmer climates keen to keep their tannin levels in check, canopy management has become an important way to dial levels down through decreased sun exposure, as has irrigation in the middle of the growing season while tannins are still accumulating in the grapes, which creates bigger berries with less tannins.

Making magic in the winery

While careful tannin management in the vineyard is key, how you extract them in the winery is equally impactful on the character of the wine, and winemakers have a number of tools at their disposal to achieve their desired fruit to tannin ratio. If they’re keen to amp up their tannin levels they can opt for whole bunch fermentation to extract tannins from the stems; prolong the maceration period, so more tannins leach out from the grapes into the wine; ferment at a higher temperature; and perform punch-downs and pump-overs during fermentation to push the grape skins to achieve higher levels of extraction.Tannins can also be managed and softened through micro-oxygenation during the fermentation process. Tannins exposed to higher levels of oxygen during fermentation will polymerise faster, leading to fruit-forward wines that are ready to drink earlier, though this process has to be undertaken carefully, as exposing a wine to too much oxygen can negatively impact its ageing potential.

Goetting of Ridge takes a lot-by-lot approach to tannin management at the Cupertino winery. “The secret to successful tannin management is being attentive to each lot throughout the fermentation process, which requires monitoring the must temperature and sugar level of each lot in each vessel multiple times a day,” he says, adding, “decisions about the type of extraction required are made based on these numbers.” Rather than micro-oxygenation, Goetting opts for “macro-oxygenation” during pump-overs – a more aggressive way of imparting oxygen into a fermenting wine, which, according to Goetting, “helps to keep the fermentation healthy while extracting tannins into the wine”.

Everything from climate and grape variety to sun exposure can impact tannin levels in grapes

Age shall not weary them

An encouraging trend happening the world over is a shared goal among winemakers to create wines with softer, more approachable tannins in their youth, inspired by a growing consumer desire to enjoy fine wines sooner. This fresh approach to winemaking is leading both vintners and critics to ponder whether fine wines with more approachable tannins have the same ageing potential as their more tannic counterparts. The jury seems to be out.“Tannins are finer and silkier universally in wines now, and because there is less bitterness on the finish, the fruits seem purer on young wines. This makes the wines more approachable, not because of greater fruit concentration, but because the fruits are better balanced against the tannins,” says Benjamin Lewin MW, who wonders whether softer tannins may speed up a wine’s evolution, and therefore lessen its ageing potential. “In terms of the long-term development of red wines, the balance between tannic structure and fruits is crucial. Once the tannins have all resolved, what is there to hold the wine together?” he questions.

Peter Sisseck of Pingus believes that starting off with high quality, finer tannins lessens the need for oxygen during the fermentation process. “You have to be very careful not to overdo it, or you end up oxidizing the other elements in the wine,” he warns. “A lot of modern wines have a tendency to age faster, which I think is down to them having riper tannins that don’t have the same stamina against oxygen as older wines,” he says, pointing out that tannins play an important role in the fine wine ageing process through being antioxidants. “The more rugged the tannins are the more oxygen it will take to ‘polish’ them,” he says. “Ripe tannins take less oxygen to polish, so you could conclude that the wine would age faster and take less time to reach its plateau of drinkability, but, if stored correctly, it would probably remain at this quality level for a long time.”

A question of balance

While Goode believes micro-oxygenation has its benefits, hard data on the process is in short supply, forcing winemakers to “fly blind” when it comes to judging the correct levels to work with. “It’s likely that oxygen applied at the right time and in the right quantities can have a beneficial effect on the mouthfeel and structure of red wines, but as yet there’s no clear evidence as to the sorts of tannin modifications that are taking place,” he says. For Goetting, wines with a high tannin profile in their youth have a better chance of ageing gracefully. “If there’s not enough structure in the wine to support the acid and alcohol, the wine might not age well and could be perceived as diluted or weak with a short finish,” he says, stressing that “young tannins must be in balance with all of the other components in the wine in order for it to age well”.

Sarah Heller MW remains on the fence regarding tannins levels and a wine’s ability to age. “In my experience of tasting Barolo and Barbaresco for 15 years, I can’t say that I’ve observed an overwhelming trend in the ageing trajectory between those with robust, austere tannins and the smoother, more rounded styles,” she says. “The worst is when a 30-year-old wine still has fist-tight tannins but no fruit left, which I have sadly experienced.” Heller is, however, happy to see winemakers in Italy working towards creating wines that are more approachable in youth due to their more refined tannins. “The most advanced regions in Italy are opting for gentler extractions paired with extended ageing in medium and large format oak barrels, and sometimes even agitating the lees for mannoproteins that help smooth the mouthfeel,” she says.

While tannins remain a complex topic that requires further scientific enquiry in order to fully understand the way they behave in wine, and exactly how they impact the ageing process, the global shift towards creating wines with more refined and approachable tannins can only be a good thing for drinkers keen to enjoy the best that the wine world has to offer without having to wait over a decade to pop the cork on their beloved bottles.