We welcomed a new pooch into our homes last week (a Shetland collie, at least this is what the animal welfare said, we still need to see how he turns out, but the early signs looks promising). Looking at the dogs running amok in our back yard, while sipping on some Shiraz, I thought about tannins in red wine and how these can relate to our K9 friends. Red wine has two distinctive characteristics that distinguish it from white wine, the colour and the mouth feel. The colour is due to anthocyanins, which I wrote about a few posts before. The astringency and fuller mouth feel are mostly influenced by tannin compounds. Tannins in grapes are is a complex group of compounds consisting of mainly catechin derived subunits. Most of the tannins in red wine comes from the grapes and are collectively known as condensed tannins. Those originating from wood are not really very stable in an acidic medium such as wine and normally start to degrade in the wine quite quickly, hence the name hydrolysable tannins.
The main source of condensed tannins in red wine is the grape berry itself. Tannins in red berries occurs in the skins and seeds and with advanced analytical methods we can distinguish to a certain extent between seed and skin derived tannins. Tannins in red wine consist of different subunits, which can bind to each other at different places, thus making the tannin chemistry of red wine very complex. We had a Master’s student working on only a small group of tannins and by using the most advanced analytical techniques money can currently buy it still took her almost 18 months to complete her data analysis of the results! In any case, even with our current relative “crude methods” we can start to characterise these tannins to a degree.
Winemaker would often separately taste the seeds and skins of red berries when deciding on a harvest date. The seeds normally taste different than the skins, due to the tannins in the seeds being more reactive with the proteins in our oral cavity, eliciting a more bitter taste and astringent mouthfeel. One reason for this is that the seed tannins are smaller than the skins tannins. Skin tannins are the Border collies of the wine world, a bit larger, softer and more playful; while those from the seeds are the Jack Russels, smaller, but more feisty. Over time these tannins undergo a number of conformational changes in the grapes during ripening and in the wine, becoming larger compounds and thereby tasting less aggressive. The smaller tannins thus gets larger, changing into compounds that first become less bitter and more astringent and eventually softer, which happens also during wine ageing in the barrel and bottle. In the next post I will write about the extraction of these different types of tannins during alcoholic fermentation and what the winemaker can do to affect this, but suffice to say that the grapes’ tannin composition will have a huge effect whether you end up with a Chihuahua or Pitbull in your glass!