When it comes to red grapes, any winemaker wants to extract grape tannins. Not only do they contribute towards colour and texture, but also aroma. The challenge with heterogeneity is that green tannins will also be extracted during fermentation. Another challenge is that there will be less useful tannins available for extraction. What to do?
One should avoid cold maceration and rather opt for a hot, short fermentation. For instance, instead of fermenting at 23°C, rather 26°C or even higher. This will give more extraction, but lessen the time that good (and bad) tannins can be extracted. This might sound paradoxical, but we’ll soon get to a possible remedy. The higher temperature should also speed up the ferment. The number of pump-overs should decrease towards the end of the ferment, otherwise too much green tannins will be extracted. In other words, the grapes should be treated quite gently towards the end, because the higher alcohol concentration will increase tannin (good and bad) extraction. For smaller tanks, less punch downs towards the end are recommended. If possible, a closed system will be beneficial (for bigger tanks) and topping with C02 gas at the end of a day and after each maceration event will also prove useful for smaller open top fermenters. Why? Because oxygen needs to be excluded, more about this later. You can also press a bit earlier, possibly at 7°B already and then continue with the ferments sans skins. What about yeast and enzymes? Choice of yeast should be Anchor NT 202®, Anchor NT 50® or Fermicru VR5®. Enzyme choice would be Rapidase Extra Color® (the artist formerly know as Rapidase Ex-Color®). The timing of this enzyme is important, but we’ll get to this later.
Now for the very interesting part… additions! Grape proteins are indiscriminate and will bind to any tannin (good or bad) and the tannin is thus lost. We don’t want this. In this case there are already insufficient ripe tannins (read good tannins), so the remedy would be to add sacrificial tannins, in order to save good tannins from binding with proteins and forever losing them.
These added tannins thus “scavenge” grape proteins and saves the good/ripe tannins. Another function of these tannins is that they can contribute towards structure and taste. So yes, the grape might be lacking in ripe tannins and have too much green tannins, but the added tannins contribute towards more “pleasant” tannins again (albeit artificial) and thus the end quality of the wine.
The winemaker probably needs to do some research and trials and make a decision about their possible addition. There are many tannin products (oak and grape derived, for instance) on the market, the best would be to discuss the application of these products with your distributor.
Rot might be a factor, so the laccase enzyme has to be considered too. The winemaker has to judge the level of rot and make a call on treatment. Laccase is a protein, which will, like grape proteins, also be bounded by tannins. The addition of tannins will bind laccase and thus remove it from the “equation”. And this is where we come to sulphur. Oxygen, in combination with laccase (should it be present) cause enzymatic browning of juice. You definitely don’t want this, so this is why oxygen needs to be excluded (as earlier mentioned), particularly at the beginning of fermentation. Sulphur dioxide will lessen the oxidative effect of oxygen. Total sulphur could probably be increased to 60ppm (if there is indeed rot).
The timing of enzyme addition for colour extraction is important. Rapidase Extra Color® should not be added at the beginning, but rather towards the middle or end of the ferment. The reason is that the tannins added will bind to it and decrease activity.
Untoasted oak chips are used for :
Intensification of fruit expression (remove green aroma)
Intensification and stabilization of color
Augmentation of volume and structure (natural polysaccharides lend sweetness to the wine, even as extraction reinforces tannic structure in the mouth)
Increased sweetness (both red & with wines)
Addition should be done while filling the tank, at the destemmer (preferably a small chip size). La Littorale recommends 50 to 150 g/hL on white must and 100 to 300 g/hL on red must.
For Boisé France, 0,25 g/L to 10g/L. The dose will vary from supplier to supplier.
Bernard Mocke is a Technical Consultant for Oenobrands