What we think of as the taste of something is the result of quite complex interactions between several different kinds of stimulus. From the taste buds, we get the five or so basic flavour elements - salt, sweet, sour, bitter and umami. This is the savoury taste of glutamates (including MSG), which was only established as a taste of its own in 2000; previously monosodium glutamate was only known to affect our perception of taste by acting like a neurotransmitter, increasing the overall sensitivity of the taste buds. This is why you will usually see it listed as a flavour enhancer, not as a flavouring. Salt can also amplify the response of the taste buds, probably by acting as an electrical conductor; it turns out that a small amount of salt added to a sugary solution, for example, can increase its perceived sweetness by up to 40%. These five kinds of flavour sensing - to which fat and astringency should perhaps be added - are classed under the heading of gustation. There is more on the chemical basis of gustation here.
Several other sensations arising from the mouth are also important in taste perception: These include the interestingly different hot feelings we get from chilli, black pepper, ginger, horse radish and so on, which are the result of the chemical stimulation of pain and temperature sensors in the tongue and surrounding area; the sensations caused by onion, garlic and their ilk involve some of the same nerves and along with spicy heat they are classed as trigeminal sensations. The astringency of tea, red wine and some fruits and vegetables, as mentioned above, is another important factor in many tastes; so too is the cool feeling we get from mint and spices like cardamom and to a lesser extent cumin, caused by their local anaesthetic action. Texture can also make a big difference to the experience of food, partly by changing the way we think of the taste. Traditionally the effect of fat on taste has been put down to the way it changes a food's texture, which is obviously at least part of the story - but there is now some evidence that it is best considered another fundamental mode of gustation.
Aromas are about as central to the taste of a thing as the signals we get from the taste buds; a bland dish can often be transformed into a 'tasty' one by adding something with a strong smell but no power to stimulate the taste buds (try adding a little toasted sesame oil to something like porridge, for example). This interdependence goes both ways; some smells can be detected at much lower concentrations if someone is simultaneously tasting an associated flavour.
Finally, what someone thinks about what they are eating makes an enormous difference, which is one reason presentation is a vital skill for a chef. Try telling the difference between a raw potato and an apple with your eyes closed; it can be done, but it's a heck of a lot more difficult than you might imagine (note: raw potato is indigestible and can make you ill, so don't eat too much). Another test is to give glasses of green-coloured orange juice to people with and without blindfolds, and see what they think of it.
(site-wide visits since 14/05/2005)