The tannins used in winemaking: are they a useful instrument or just a comfortable shortcut?
I left London to go to Verona on the day before the Vinitaly begun, because BA doesn’t fly on Valerio Catullo’s airport every day of the week. As I was expecting, on my flight there were many known faces, from the famous journalist to the good importer, from the pushy salesman to some ex colleague. I’ve had the luck of travelling with an ex colleague and good friend that was going to be met in Verona by another old acquaintance, a girl dealing in yeasts and additives for winemaking. Once landed in Verona, I stay behind to say hello, and I am promptly invited to join the group in a quick trip to the winemaking school of San Michele all’Adige, to follow a masterclass on the use of tannins in winemaking. The speaker was going to be Gianpaolo Benevento, working for Silva Chimica, a firm leader in the production of tannins.
I didn’t have any appointment in Verona on that day, so I went along. Yes, I initially meant to go straight to the hotel and get some rest (as I got up at 3.30 am to catch my flight), but then I thought:
1. Occasions like this don’t come around very often;
2. It is well known that the Vinitaly is very tiring, so I can well start to spend my energies now.
Once in San Michele all’Adige and found the classroom, we sit down to hear the lesson. I only had one doubt: that my very limited chemistry knowledge would impede me to understand much of what was going to be said. Luckily this revealed to be true only in part, as the speaker was brilliant in his exposition and ventured into pure technicalities only if someone expressly requested it. This masterclass helped me to shed some light onto this obscure subject. Why obscure? Because if we’d try to ask 100 wine experts why do they think that tannins are added during wine production, the vast majority will answer “to add structure and astringency”. But things aren’t quite like that. Finally I’ve also understood why different kinds of tannins are used and in different stages of the wine production too.
But let’s get into the detail. Tannins used in winemaking are divided into two big families: the hydrolysable tannins and the condensed tannins. The hydrolysable tannins are those ones which are easily soluble in water, and they are of two different kinds: gallic tannins and ellagic tannins. The gallic tannins are extracted from the Tara tree (http://en.wikipedia.org/wiki/Tara_tree) or from the oak gall nut. The ellagic tannins are extracted from oak trees or chestnut trees. The condensed tannins, or proanthocyanidinic tannins, are those extracted from  the grapes (skins and pips) and those extracted from the Quebracho tree.
To understand why these tannins are used in different moments of the wine production, let’s see what (further than the solubility in water) makes them so different one from another. The hydrolysable tannins have antiseptic properties. Furthermore, they are excellent antioxidants and excellent complexators of proteins. On the palate they are astringent, and they are quite compatible with sulphites. Their colour ranges from a light shade of yellow to dark brown. Condensed tannins are good antioxidants (all tannins are) but not excellent ones. These tannins can chemically react with the anthocyanins and bond with sulphites. Their astringency on the palate is quite limited and their colour ranges between red and dark brown. To know all the characteristics of the individual tannins is very important to understand their utilization: let’s see them one by one.
The chestnut tannin is always brown in colour and has a typical lightly-charred-wood aroma. It is used at the beginning of the fermentation to inhibit the oxydising enzymes and so to prevent any unwanted oxidation. Being also an excellent antiseptic, it improves the effect of the SO2 allowing the winemaker to use less of the latter. The use of this type of tannins is normally limited to the production of red wines, and it is warmly recommended at the beginning of the alcoholic fermentation, and never after the malolactic fermentation, as it could impart some unwanted herbaceous notes to the wine. Confess, you are starting to understand a bit better now… But let’s move on.
The Quebracho tree tannin is red-brown in colour and has a typical aroma of bread crust. Thanks to its excellent effectiveness in precipitating proteins, it has been used in winemaking since ages. Furthermore, after its colour-stabilising properties were discovered, its utilization is in constant growth year after year. Of course if it is used at the beginning of the fermentation to precipitate the proteins, then it won’t be available later on to stabilize the colour (anthocyanins), so its use is recommended only after the protein precipitation. To precipitate the proteins you should use chestnut tannins, which cost 10 times less than the Quebracho ones. Its dosage varies depending on the grape variety used and also on the type of fermentation that you are carrying on. In a fermentation that foresees a long maceration, you will also extract some of the pips tannins, which will contribute to stabilizing the colour. Now think of all the fermentations with very short macerations that result in wines with an unbelievable depth of colour… Oh, the Quebracho tannins are also use in the pre-bottling phase, because of their fine aromas.
The oak gall nut tannins are extracted by the leaves of a plant called Chinese gall. These leaves, when attacked by an insect, curl up on themselves and enrich with tannins. The tannin in nature is a mechanism of self defence of a plant. If a plant contains tannins in high quantities, this won’t be palatable for the animals, which will then abstain from eating it. The oak gall nut tannins are of the hydrolysable kind. It is light yellow in colour, it hasn’t got any characterizing aromas and it is astringent on the palate. Amongst all the tannins used in winemaking, this is the most reductive one, and it is used to prevent any form of oxidation. This tannin is also used for clarification, together with bentonite. One could argue “isn’t bentonite enough to clarify the wine?” well yes…and no. Bentonite and tannin clarify the wine through different (and complementary) processes. Bentonite acts through the difference between the electric charges. Tannin acts on molecular weight. By using both, you will ensure having wines which are perfectly clear and protected by unwanted oxidations.
Oak tree tannin is of the ellagic kind and it is extracted from the wood of the Quercus Robur tree, grown in the French Massif Centrale or in Slovenia. The wood is dried and then made into chips, which are infused in hot water to extract the tannins. This tannins can be further purified in a solution of water and alcohol. Water-extracted tannins are very similar to the tannins that the wine would extract from the new oak cask in which it matures. This kind of tannin is very much used during the fermentation and not much in the fining phase, because of its astringency and the time (and amount of oxygen) it needs to soften up. Oak tannin which has been purified in alcohol is not astringent, but it retains its antioxidant properties. It is often used during the fining phase, especially on those wines that hadn’t had any oak ageing, to smooth their eventual rough edges.
A few words also on grape tannins, which can be of two different typologies: extracted from the skins and extracted from the pips. Both are condensed tannins and their cost is quite high. Because of their high cost, their use is limited to the cases of absolute need. Both tannins react very effectively with anthocyanins and are very useful for stabilizing the colour. Pip tannins contain some residues of gallic acid, therefore are better antioxidants than skin tannins. They are normally used at the beginning of the fermentation, especially for those musts that are quickly separated from the solid matter (normally this happens because the pips are unripe).
I know that the technical information can get you dizzier than wine itself: I realised that after this 2 hours long masterclass, but to conclude I would like to add a few personal considerations. The speaker told the students that tannins (and indeed any other additive) should never be seen as a way of improving a wine’s aroma or taste. That is because if you’d do so, you’d invalidate all the hard work done (in the vineyard and in the cellar) to highlight the character of grape variety and terroir. I can agree to that. On an hypothetical scale that symbolizes technology, on which 0 corresponds to no technology whatsoever and 100 cm the most daring use of technology itself, my views are represented by the 25 cm. A rough diamond wouldn’t have any chance of shining if it wouldn’t be for the work of a good cutter and his emery wheel. What would be the sense in opposing the use of an emery wheel? The important thing is that the diamond cutter doesn’t take a piece of glass and doesn’t douse it with wax, so that it shines like a diamond…