Have you ever tasted a young wine that left you with a rough, dry mouthfeel? Have you ever experienced this sensation on a persimmon, an underripe fruit, or tasting an edible wild plant? This phenomenon is called astringency. Well, astringency was the moment when you came into contact with tannins.
Tannins are plant compounds also called phenols or polyphenols. They protect plants because they interact with the proteins of their aggressors, such as animals. The everyday feeling of a smooth mouth is an illusion, due to the proteins in saliva that lubricate the tongue when in contact with the palate or teeth! Tannins from wine or underripe fruit bind to these lubricating proteins, altering their functionality. Astringency is therefore associated with a feeling of dryness in the mouth.
Tannins exert a protective effect mainly because they bind to enzymes, the protein substances that provide digestion in the stomach and intestine: an excessive consumption would inhibit digestion. This is how plants defend themselves from those who eat them! You may have had digestive problems from eating too much fruit as because you could not digest them properly.
We often love the impressions that astringency causes in the mouth: the slight astringency of cocoa, for example, makes chocolate velvety; the tea one is the main sensory note of its taste.
Mankind has exploited the reactions of tannins with proteins since the dawn of time by soaking hides in plant decoctions, the so called leather tanning. Tanning combines the tannins and proteins (collagen) in the hides into chemical complexes that are mechanically stronger and less susceptible to microbial decomposition. Incidentally, the term tannin comes from the Celtic name for oak, ‘‘tan’’, whose bark was used for tanning.
The interaction between tannins and proteins, explaining some food intake sensations and leather tanning, is one of the key aspects of the amazing chemistry of tannins: we will discover these daily companions, step by step, in the next Tannin Chronicles.
Written for Tannins.org by Marc-André Selosse