"And although he told her that for the French the preparation and eating of good food was an expression of a national trait, she discovered that for this too he suffered in vocabulary...It was as though he had travelled only the familiar, his experience of taste truncated by the absence of words to describe it...Astringent is the sixth taste. Six tastes? That's right, sweet, salty, sour, pungent, bitter...and astringent. Kashaya is a word to describe a taste for which we have no direct translation in English. The word astringent, which is traditionally used to describe the tannins in wine, or the a constricting medicine, takes on a broader meaning when used in relation to Ayurveda.
Did the fox taste the rabbit, she wondered, having no word for its brawn?"The Grasshopper Shoe, Carolyn Leach-Paholski
It's a hard taste to describe because it rarely exists alone, but it's most easily described as a sensation. It's a dry, puckering unpleasant tightness in your mouth. Bite into an unripe banana for the closest approximation. Strong black tea also gives a close feeling of astringency, but the most astringent food I know of is a little fruit native to Australia called lilly pilly.
Astringent taste consists of earth and air. It is light, dry and cooling. Astringent is less nutritive and more medicinal. Whilst all dosha's require all tastes, astringent is the most beneficial to Pitta, then Kapha, and only in tiny amounts for Vata, as it aggravates this dosha.
Astringent is the sixth taste, rather than the first because it needs to be consumed in the smallest amounts. In excess it will damage the colon. But it is difficult to overdose on astringent taste from food alone, it is usually the result of improper use of medicinal herbs.
Astringency, as you might imagine from the reaction in your mouth, contracts amd tightens the tissues. It is useful in cases of diarrhea and bleeding as it constricts and binds.
It's easy to get all the astringency you need by just adding a pinch of turmeric to your daily meals.