The structural and sensory sou
When we speak about wine from a deep perspective —whether as oenologists, sommeliers or simply passionate enthusiasts— we inevitably end up speaking about phenolic compounds. Within this broad group, polyphenols are the most abundant and the most decisive from a sensory and structural point of view. It is these compounds that explain the intense colour of a great red wine, the astringency that dries the mouth in a powerful young wine, the ageing capacity of a reserva, or the aromatic complexity that emerges over the years inside the bottle.

Phenolic compounds are not an abstract laboratory concept; they are living matter, structure, longevity and identity. To understand them is to understand a large part of the essence of wine.
WHAT EXACTLY ARE PHENOLIC COMPOUNDS?
Phenolic compounds are chemical compounds of plant origin characterised by having one or more phenolic groups in their molecular structure. In the case of wine, they mainly come from the grape —from the skin, the seeds and the stems— although they can also be incorporated during ageing in wood, especially in oak barrels.
From a chemical point of view, they are secondary metabolites of the vine (Vitis vinifera) that the plant synthesises as a defence mechanism against external aggressions: ultraviolet radiation, fungi, water stress or insect attacks.
This protective function explains why phenolic concentration is so closely linked to climate, soil and viticultural practices. Warm and dry vintages, with good sunlight exposure, usually favour greater phenolic synthesis, provided that the plant does not suffer excessive stress that would compromise its ripening.
CLASSIFICATION AND TYPOLOGY: MUCH MORE THAN TANNINS
When speaking about phenolic compounds in wine, the concept is often reduced to tannins, but the reality is much richer. Within the phenolic compounds of wine, polyphenols can be divided, broadly speaking, into two main groups: flavonoids and non-flavonoids.
- Flavonoids
Within the flavonoids we find anthocyanins, responsible for the red, purple or violet colour of red wines; flavonols, which contribute to colour stability and act as antioxidants; and condensed tannins or proanthocyanidins, responsible for astringency and for a large part of the wine’s structure.
Anthocyanins are virtually non-existent in white wines, as they are found in the skin of red grapes. Varieties such as Cabernet Sauvignon or Syrah stand out for their high anthocyanin content, whereas others such as Pinot Noir present more modest concentrations, which explains their more delicate and translucent colour.
Tannins, for their part, may come from the skin, the seeds and also from the wood. Seed tannins tend to be more aggressive and bitter, especially if they are extracted before full phenolic ripeness. This is one of the main concerns in extended harvests: achieving technological ripeness (sugar) aligned with optimal phenolic ripeness.
- Non-flavonoids
Among the non-flavonoids, phenolic acids (such as caffeic or ferulic acid) and stilbenes stand out, such as resveratrol, a compound that has generated great scientific interest due to its antioxidant properties and its possible role in cardiovascular health.
PHENOLIC RIPENESS: A DELICATE BALANCE
In modern viticulture, phenolic ripeness is a key concept. It is not enough to measure the potential alcohol; it is necessary to taste the berry, observe the texture of the skins, the colour of the seeds, their astringency. A green seed, with a herbaceous flavour and hard texture, indicates unripe tannins. By contrast, a brownish, crunchy seed with a more nutty flavour suggests more appropriate ripeness.
Many oenologists, especially in regions with a long tradition such as Bordeaux or Rioja, have insisted on the importance of waiting for this phenolic ripeness, even if this implies assuming higher alcohol levels. The aim is to avoid wines with dry, harsh or unbalanced tannins.
This decision is not trivial. Excessive ripeness can lead to heavy wines, with a loss of freshness and tension. Therefore, the true art lies in finding the optimal point at which sugar, acidity and phenols are in harmony.
MACERATION AND EXTRACTION: THE ARCHITECTURE OF RED WINE
During winemaking, especially in red winemaking, the management of maceration is decisive. Polyphenols are not immediately present in the must; they must be extracted through contact between the juice and the solid parts of the grape.
The duration of maceration, temperature, the frequency of pump-overs or pigeage, and even the type of vessel (stainless steel, concrete, wood) directly influence the quantity and quality of extracted polyphenols. A short maceration can result in lighter, fruit-driven wines, with less tannic structure. In contrast, long macerations, such as those applied in some age-worthy wines, allow for greater extraction, provided that the grape has sufficient quality to withstand it.
In Burgundy, for example, some Pinot Noir producers opt for very gentle extractions to preserve varietal finesse, whereas in areas such as Ribera del Duero it is common to seek greater concentration and structure.

POLYPHENOLS AND OAK AGEING: A SYMBIOTIC RELATIONSHIP
Ageing in barrel not only provides toasted, spicy or balsamic aromas; it also modifies the phenolic structure of the wine. Oak, especially French or American oak, contains hydrolysable tannins that progressively integrate into the wine.
Moreover, during the natural micro-oxygenation that occurs through the pores of the wood, the wine’s tannins polymerise, that is, they bind together forming larger and less aggressive molecules. This process is fundamental to soften astringency and stabilise colour, especially in wines intended for long ageing.
The combination of grape tannins and wood tannins requires precise management. A new barrel can contribute a significant tannic load; for this reason, many wineries combine different proportions of new and used oak to avoid imbalances.
COLOUR, STABILITY AND BOTTLE EVOLUTION
The colour of a young red wine is mainly the result of phenolic compounds, especially free anthocyanins. Over time, these react with tannins and other compounds to form more stable pigments. These reactions explain the transition from an intense violet colour in youth to ruby, brick or garnet hues over the years.
The ageing capacity of a wine is closely linked to its phenolic content and quality. Wines with solid tannic structure and good acid balance usually have greater ageing potential. Nevertheless, the quality of the tannins —their ripeness and integration— is more important than their absolute quantity.
In white wines, although the phenolic load is lower, polyphenols also play a role in oxidation and aromatic evolution. In some styles, such as white wines fermented with the skins (the so-called “orange wines”), the phenolic presence is much more noticeable, providing texture and an unusual ageing capacity in a traditional white wine.
HEALTH, SCIENCE AND MYTH: THE CASE OF RESVERATROL
The debate about polyphenols and health has been intense in recent decades. Resveratrol, present in the skin of red grapes, has been the subject of numerous scientific studies attributing to it antioxidant properties and potential cardiovascular benefits. This compound was one of the factors associated with the so-called “French paradox”, which observed a lower incidence of coronary diseases despite a diet rich in fats, possibly linked to moderate red wine consumption.
However, the scientific community insists on caution: positive effects are always associated with moderate consumption and within a healthy lifestyle. Wine is not a medicine, but a cultural beverage with bioactive components.
A FINAL PERSPECTIVE: UNDERSTANDING PHENOLIC COMPOUNDS TO UNDERSTAND WINE
To speak of phenolic compounds —and especially of polyphenols— is to speak of structure, texture, colour and time. It is to understand why a wine seems silky or rigid, why another can age for decades and some fade within a few years. It is also to acknowledge the silent work of the viticulturist in the vineyard and the oenologist in the winery, seeking balance between extraction and elegance.

Ultimately, phenolic compounds are one of the great interpretative keys to wine. Knowing them allows us to taste with greater awareness, to better appreciate the work behind each bottle and to delve deeper into this millenary beverage that combines science, nature and culture in a single glass.
Goodbye for now, and see you soon.














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