As we enter the fourth heatwave of the year and reach for yet another bottle of sunscreen, it occurs to me that red winemaking might take on particular significance this season. That thought led me to reflect on the role tannins play – not only in protecting the vine, but also in shaping the structure, style, and ageing potential of the wine itself.
Much like our cultural attitudes toward getting a suntan have shifted over the decades, wine profiles and tannin use have also evolved. Twenty or thirty years ago, “big tannin” was often synonymous with prestige in certain red styles; today, the emphasis is on low intervention, balance, and integration. Viticulture and winemaking practices have adapted accordingly, reflecting changing consumer tastes, shifting climates, and a far better scientific understanding of phenolic chemistry.
Recent research has been particularly revealing. Studies have explored tannin extraction during maceration, varietal differences in extractability, and the reported ability of certain tannin additions to bind and reduce sulphurous off-odours. Such findings underline why tannin chemistry remains an active and important area of study – it is fundamental to taste, texture, aroma stability, and wine longevity.
Tannins occur naturally in the berry and vine but can also be introduced exogenously during winemaking, or extracted during a wine’s ageing and maturation in barrel. In this article, I’ll explore both: first, the sources and behaviour of tannins in the berry and vine; then the sources and applications available to winemakers during fermentation, ageing, and maturation.
The technical term for grape tannins is polyphenolic secondary metabolites, primarily proanthocyanidins. Their primary role in the plant is defensive – shielding against sunlight damage and deterring consumption of unripe fruit through bitterness and astringency. This astringent sensation is caused by tannins binding to proteins in the mouth and palate. As grapes ripen, the perception of tannins changes through oxidation, polymerisation, and interactions with other phenolic compounds, as smaller molecules link to form larger ones.
For winemakers and growers, the most relevant tannin sources within the grapevine are the skins, seeds, and stems. Other plant material, such as leaves or woody matter, should be removed prior to processing. The skins are the primary source of tannins in most red wines, with concentration and composition strongly influenced by sunlight exposure – often higher in brighter growing seasons. Extractability and composition also change as ripening progresses, affecting the quality and character of the tannins available at harvest. The grape variety and clonal type also have an effect on the tannin profile and the sizes of the berries themselves should there be little or heavy rain around the harvest period leading to concentration or dilution respectively.
With rain and damp conditions the risk of fungal disease pressures can lead to tannins being affected and losing the structure as well as colour instability. Choosing when and how to leaf strip is therefore of critical importance but difficult to predict what the medium term meteorological conditions will look like. The seeds don’t lie and right maturity and readiness for harvest is often seen when the seeds are lignifying and turning brown.
As tannins sit in the category of phenolics and total phenolics rise during these hotter spells it is also important to be aware of those phenolics extracted during heavy pressing that will readily oxidise down the wine making process and tend to be better dealt with during the must phase than later post fermentation.
As the grapes are passed onto the winery post harvest there are many different options the winemaker can utilise to enhance or correct tannin extraction. At their core tannins as a chemical group are a natural anti-oxidant or rather they bind the incredibly reactive element that is oxygen.
The winemaker can utilise tannins during the fermentation and ageing phases of the winemaking process with a vast array of methods, products and containers such as barrels and foudre’s to enhance, remove or balance the tannin and structure. Cold soak maceration with skin and without seeds or with seeds and skin can reduce or increase the astringency, ethanol production during fermentation will hasten tannin solubility which may be desirable when receiving lighter skinned grapes.
Manipulating the fermentation temperature is also with heat increasing extraction and the management of the cap and how this is punched down or pumped over also changes the extraction with gentler passes favouring skin extraction and heavier aggressive punch downs drawing more seed tannin extraction.
All of these mechanisms and manipulations are part of the excitement and dare I say magic of winemaking as there are so many complex reactions happening with many factors to consider (or not) it is a shame that reds globally have fallen on hard times. Exogenous tannins (from various wood sources but primarily oak) is another area that winemakers can call upon should they need additional help in order to control disease and precipitate laccase from botrytised grapes or stabilise colour during fermentation and there are a wide range of products available targeting specific requirements.
Most interestingly the purpose of tannin management is to achieve something where the initial bitterness from smaller low polymer tannin molecules polymerise over time giving way to large more complex groups where astringency and binding to the salivary glands can lead to a silkier finish.
The ageing related tannins are controlled and changed through different means and something I will expand on in combination to the tertiary aroma article later in the year but they encompass three main areas;
Oxygen management – Controlled oxygen exposure encourages tannin polymerisation but too much oxygen can strip fruit and harden tannins.
Oak maturation – Barrels (and to a lesser extent, staves or chips) contribute hydrolyzable tannins from oak, adding oxidative buffering, mid-palate weight, and complexity.
Ageing tannin additions – Grape-derived or wood-derived tannin preparations can strengthen colour, improve oxidative stability, or add structure.
Tannins – and the art of managing them in both the vineyard and the winery – can feel overwhelming in their range of variables and possible approaches. Yet, as in many aspects of life, timing is everything. With careful observation and well-judged decisions, the coming months can stay on course for a positive vintage.
So, to the harvest class of 2025: wear sunscreen – literally for vineyard managers and crews, and figuratively for winemakers and cellar hands. And at least once during harvest, take a break, breathe, and listen to Baz Luhrmann’s Everybody’s Free (To Wear Sunscreen). Good advice, in winemaking and in life.
