Heat is indeed a tactile sensation, which is why capsaicum (sp) is used in topical creams. It tricks the nerves into thinking heat is applied to the skin, tounge, lips, etc.
Bitter comes from base, or in other words, from alkaline foods, while sour cames from any of the acids. Sweet of course comes from those compounds that have a chemical make-up very similar to sugar. Salty comes from some sodium base compounds such as sodium chloride, while other sodium based compounds give a bitter, or soapy flavor (sodium bicarbonate).
Most flavors are a combination of the 5 basic flavors, and are heavily influenced by the sense of smell. It has been determined (and the guy won last year's Nobel Prize for his efforts) that smell is a recoginition by the brain of the "firing order" if you will of the many nerve types in the olfactory system. That is, the order that the nerves fire in determines the odor recognized. This info is then combined with information from the taste buds to give you the total "taste" experience.
Ever wonder why food tastes so much better when you're camping? It's because the odors present in the forest, or on the riverbanks, or wherever you are, are associated with pleasure, and enhance and compliment the flavors of the food you are eating.
It's pretty complicated stuff.
Here's something else to throw at you. Vanillan, the artificial vanilla, has a molecular structure identical to vanilla. But it is a sythesized molecule, and is therefore required by law to be labled as an artificial flavoring.
Acids and alkalies both work by either taking from, or adding to the electrons in the outer valence rings of molecules, thereby changing that molecule. If you put copper into sulfuric acid, there is no loss of material. It's just that the copper becomes copper sulfate (really stinky stuff). The metallic copper is no longer a coherent metal, but has become part of an ionic compound. The same thing happens when strong acids or alkalies touch your flesh, or toungue. There is a reaction where your skin, or whatever is affected, either gives up electrons, or is given electrons, which of cours destroys the skin by changing the molecular structure.
That's in fact why baking soda and vinegar produce carbon dioxide bubbles when mixed together. The sodium bicarbonate compound is destroyed, with the sodium held in the acidic suspension, while the stable carbon and oxegen molecules are released within the liquid.
I know, I get a bit tehnical sometimes. But that is essentially what's going on. The explanation may not be exact, but it's close enough to provide a bit of understanding.
If you've ever eaten a piece of extremely sharp cheese, it can leave blisters on your tounge, from the strong acid content. This happened to me after eating some very sharp Swiss Cheese one time. It tasted great to me, but left me with a sore mouth before I knew what was going on. Meat tenderizers such as papain and bromelain do basically the same thing, but specifically with protiens. The protiens are denatured, or altered by the powerful enzymes.
Ok, enough of chemistry 101. Hope I haven't confused anyone.
Seeeeeeya; Goodweed of the North
