Polyphenols evolution from grape into wine

Polyphenolic compounds are substances naturally included in grapes which tend to progress during wine maturation and production phases. They are characterized by one or more phenolic rings: thanks to them and other compounds we obtain the color of the final product. They can be present in all the parts of the bunch, grape peels, grape seeds and stalks.

They can be found above all in red wines and they are the result of the musts in contact with grape peels and grape seeds. Wine tannins depend certainly on vinification technique, but above all on the intrinsic characteristics of the vine. Furthermore, being part of antioxidants, polyphenols ensure that wine is maintained over time.

Polyphenols evolution in grape:

From veraison, or when the grape changes color from green to intense red, the tissues of the vine are enriched with phenolic compounds. Anthocyanins appear from veraison and their peak occurs at maturity to then subsequently degrade with over-ripening.

Even the tannins present in the peel have a similar trend, while for the grape seeds the trend is different: the concentration of tannins decreases as the harvest time approaches.

These trends may vary according to the territory of the vineyard.

Polyphenols categories in grape:

• Flavonoids: from flavo = "yellow" compounds, mainly located in the skins of the berries.
• Anthocyanins: dark pigment compounds of grapes also located in the skin.
• Tannins: found in the skins, stalks and grape seeds, they have catechin as a precursor.

Tannins evolution through the time:

Wine tannins, when tasted, are responsible for the sensation of astringency. This sensation is due to the fact that the tannins are able to condense saliva proteins.

Over time, the "hard" and "bitter" sensation of the tannins fades, making the wines “silkier” and "enveloping". The characteristics of the tannins vary over time, the molecules in the wine aggregate, passing from small sized molecules to heavier and more complex compounds.

These phenomena called "polymerization" and "precipitation" are also the cause of the variation in the color of the wine.

Green tannins, on the other hand, are typical of low quality wines that have extracted less valuable tannins during production. In this case, the tannins in the wine can have herbaceous and bitter sensations.

How to decide the harvest time:

At Centro Analisi CAIM in Follonica we offer services that can help the oenologist choose the right time to harvest the grapes. With the analysis of the Phenolic Maturity we can monitor the grape maturity progress in order to be able to harvest them with the right balance between the phenolic component, sugars and total acidity.