When you pop a sweet pan (betel leaf) into your mouth, there is an explosion of sensation. The bitterness of the leaf itself, the sweetness of the gulkhand, the pungency from the clove, the sourness from the lime, amongst others, combine to give all the taste buds a little something. Popularly, there are five taste sensations that our tongue registers – sweet, salty, bitter, sour and “umami”, Japanese for “deliciousness”.
These tastes are registered by taste receptor cells. Residing inside little pot-like structures called taste buds, are bunches of taste receptor cells. Current evidence suggests that each taste receptor cell expresses receptors for a particular type of taste, such that all five tastes are sensed by each bud. However, the ratio of receptors can change between taste buds, such that some tastes are experienced more intensely in specific parts of the tongue. For e.g., sweetness is most acutely felt on the tip and front of the tongue. Once “activated” by a particular taste, taste receptor cells release neurotransmitters which conveys the message to a sensory neuron that relays it to the brain. This one-step messaging service means we register a taste almost instantly, which is why it is hard to mask your dislike of a food served by a much-loved aunty.
In Ayurveda, each food item is ascribed a taste (rasa) and these are differently recognised. There are six taste (rasas) : Sweet (madhura), salty (lavana), bitter (tikta), sour (amla), pungency (katu) and astringent (kashaya). Food items are accepted to contain all the rasas, but may exhibit dominant rasas, for e.g., while the dominant rasa for Grapes is sweet, it also contains astringency. Of all the tastes, astringency is uniquely mentioned only in Ayurveda. It is experienced as a dryness or puckering oral sensation. A commonly used ingredient in Indian food with astringency dominant is coriander (dhaniya) seeds powder.
Examples of modern foods with dominant astringent taste are: tea, wine, unripe bananas and cocoa. What’s common among these foods are a high polyphenol content. There are two properties of the astringent taste which makes it interesting. First, astringency may not be sensed by the taste receptor cells, but instead by the trigeminal nerve directly . Second has to do with how astringency is perceived. Typically, intensity of tastes decreases with repetitive sampling i.e., after eating a jalebi, milk doesn’t taste sweet anymore. But with astringency, its perception increases with repetitive sampling, which is perhaps why it is easy to reach again and again for that sip of red wine!