The Science of Tannins
The term ‘tannin’ derives from the Latin tannum, meaning ‘oak bark’. Dating back to around 6000BCE, the bark of oak trees was used for tanning animal hides into leather. Known as ‘vegetable-tanning’, this process produced leather goods by using tannins sourced from the bark of oak trees. By applying these to the skin before stretching it out on a frame, the hide would lose moisture and absorb the tanning agent.
Tannins work by binding to the collagen proteins present in skin, causing them to become less water-soluble and thus more resistant to bacterial attack. This process introduces antioxidants into the skin, which affords the hide greater flexibility and prevents natural decomposition by preserving collagen. Put simply, tanning replaces the natural water molecules present in skin, and the less water present, the less likely it is to rot.
Nowadays, animal tanning can be done more efficiently using modern technology and minerals such as chromium sulfate, invented in the mid-nineteenth century. However, when it comes to wine, we’re old-fashioned, and oak remains our number one companion.
In addition to the bark of oak trees, tannins can actually be found in abundance throughout nature. What do rhubarb, tea, cranberries, walnuts, and grapes all have in common? They each have a high presence of naturally-occurring tannins.
Biologically, the purpose of tannins is to deter animals from eating a plant’s seeds or fruit before it has ripened. You may have noticed that all the aforementioned items provide (with varying degrees of severity), a sort of mouth-coating astringency. That is, they give your mouth a dry feeling that makes you feel as though you need to ‘chew’ it out. Often, wines with high tannins will also be described as ‘chewy’. When well managed, tannins can add a pleasant kind of bitterness.
Tannins in Wine?
When it comes to wine, there exists four primary sources of tannins; the grape seeds, skins, and stems, and the wood barrels that are used for ageing a wine. As well as adding to the weight and structure of a wine, tannins provide greater texture by changing its mouthfeel. In the barrel, tannins are released from the skins and seeds of the red grapes as they soak up the juice. The strength of a wine’s tannins depends on the length of time the skins and seeds have spent soaking in the juice within an oak barrel. As white wine ferments without any skin or seeds present, it is always less tannic, as its only source of tannin comes from the oak barrel.
By macerating skins, pips, and juice altogether, both colour and tannin are diffused into red wine.
As such, heavy tannins or ‘chewy’, ‘grippy’ qualities are much more commonly associated with red wines.
When producing red wine, you want the skins to impart lots of colour, which adds more tannins to the juice and deepens the complexity of the wine. The anti-oxidizing qualities of tannins are not only handy for producing leather, they also protect wine. By acting as a natural antioxidant in big wines such as Cabernet Sauvignon, tannins protect from spoiling, meaning the wine can be aged for many years.