Sparkling carbon dioxide, spicy mustard that prickles the nose (allyl isothiocyanate), the heat of chilli * (capsaicin), the scratch of olive oil at the back of the throat (oleocanthal), the cool of mint (menthol), the astringency of tea (tannins), and also the temperature of food – all these sensations derive from the trigeminal nerve, independently of the gustatory and olfactory pathways.
Various molecules activate ion channels present in the receptor cells of the peripheral nervous system, particularly those concerned with the detection of temperature, thus sending back a “false” impression of hot or cool.
Astringency, perceived while tasting certain red wines, tea (especially if it’s been stewing for a long time in the pot), or even raw artichoke leaf, derives from the ability of tannins to impact saliva proteins **, lowering their lubricating power and provoking a “dry” feeling in the mouth.
But that’s not all – temperature also muddles our senses. A warm tart tastes sweeter than a cold one. The same goes for melted ice cream, which often seems too sweet. This is due to the fact that, in the central nervous system, the same cell can respond not only to taste stimuli but also to tactile, thermal or olfactory stimuli.
Mix in physical sensations linked to texture (the stickiness of coconut rice, the crunchiness of cookies, the chewiness of squid), and you begin to understand the extent and diversity of the signals that flood our brains when we eat!
* The heat of peppers is measured on the Scoville scale, which rises from 0 for food without any detectable spiciness (like bell peppers) to 16,000,000 for pure capsaicin (the active component of chilli peppers), via 2,000 for Espelette pepper, 40,000 for Cayenne pepper and up to more than 1,200,000 for the aptly named Trinidad Moruga Scorpion, which holds the record for the world’s strongest pepper!
** It is precisely by using vegetable tannins that humankind developed the process of tanning skins to transform them into leather – which is rot-proof, flexible and water-resistant, thanks to the chemical bonds favoured by the tannins between the collagen fibres (proteins).