The Mayan Indians had the right idea about chilli: eat it with great caution, but inflict it on those you don't like without mercy. Unfortunate enemies of the tribe would retreat from battle under a hail of the spicy peppers, though it is not recorded whether the Mayans then ran after them to pick up their fruity weapons, which they also used, presumably rather bruised, as currency.

But when it came to their cuisine the Mayans really knew how to treat chilli with respect. They even had a word for it: huuyub. That is, to pucker one's mouth and take a sharp intake of breath after taking too large a bite of a chilli.

Chillies have always occupied the more hardcore end of the cookery scale. Few other seed fruits, after all, hold the dubious distinction of having been used as instruments of torture. Powdered chilli has traditionally been used as a weapon in India, to particular effect when thrown in the eye of an attacker. It also forms the basis of pepper sprays, used increasingly in place of other chemicals by police forces to restrain offenders.

But it seems the chillies we have known until now have been feeble things, mere kormas compared to a killer vindaloo waiting to be sampled. Scientists recently unveiled a variety of pepper that makes all that has gone before seem about as spicy as a cucumber-and what's more, it does not even come from the new world where the fruit originated.

This new pepper, the naga jolokia or Tezpur chilli, is so hot it is reputed practically to induce heart failure in anyone who hasn't grown up with its intestine-stripping qualities. And it is not from New Mexico or the Caribbean, but from India. The Mayans may have liked their food spicy, but put them up against a bunch of kids from the banks of the Brahmaputra river in Assam, north-east India, and they would be ordering another pint and making a dash for the bathroom like the rest of us.

The reason behind the Tezpur chilli's almost inedible hotness is its extraordinary high concentration of capsaicin, the chemical in chillies that produces their characteristic burn. Chilli heat is measured on a sliding scale developed by Wilbur Scoville, a chemist working for the Parke Davis pharmaceutical company, in 1912. His "organoleptic test" involved five volunteers sampling a sugar solution containing ground chilli paste in increasingly dilute concentrations, until they could no longer detect the chilli burn. His method was replaced in the 80s with a rather more scientific test based on liquid chromatography, but chillies are still measured in Scoville units. To give some measure of the Tezpur chilli's eye- watering pungency, jalapeno peppers merit about 5,000 points on the Scoville scale. The Tezpur scores 855,000.

One might, in fact, be well placed to prosecute a chef serving up Tezpur con carne for grievous bodily harm. This is because the way we "taste" chilli in dishes is not entirely to do with our sense of taste. As Dr Len Fisher, a biophysicist and food writer from Bristol University, England, notes, the suspicion that eating a raw chilli is all about pain has a strong basis in chemical fact. "The tongue is the thing that picks up taste: sweet, sour, salt, bitter and umami," he says. "Your mouth is also full of pain receptors that will send nerve signals to the brain. The chemical capsaicin can bind to these pain receptors and set them off like a switch so your brain is interpreting them as pain and damage to the tongue."

The chemical does not get less potent during cooking, and is also extremely resistant to being broken down in the intestinal tract, which is why one can enjoy a very hot dish more than once in its journey through the body. The capsaicin burn will be detected on any mucus membranes, such as the inner nose, eyes and sex organs, hence the advice to wash very thoroughly after preparing chillies and before using the bathroom. As Fisher notes delicately, "once capsaicin binds to a receptor it binds very strongly and is rather hard to move." But, he adds reassuringly, capsaicin does not actually cause any damage to the body, despite sometimes emphatically giving that impression.

This knowledge is little comfort when your insides are being burned to a crisp, however. Neither does it explain why we continue to eat curries and chillies in ever-increasing strengths when the sensation is often so very unpleasant.

This has to do with the fact that capsaicin also prompts the release of endorphins, the body's natural painkillers and "feelgood" hormones. In fact, capsaicin and chillies in general are full of health-giving properties. Chillies contain twice as much vitamin C as citrus fruits, and the dried fruit is an extremely rich source of vitamin A. Even its "pain" inducing qualities can be beneficial, since repeated exposure to capsaicin dulls the pain receptors. This allows curry fans to eat increasingly hot dishes, but also explains the efficacy of capsaicin cream in treating conditions like arthritis.

Kalim Mir, proprietor of the award-winning Darmar restaurant in Manchester (England's famous "curry mile") explains the preference for chillies in hot countries like Mexico and India by their sweat-inducing property. Chilli makes you perspire, he says, which cools down the body, allowing you to eat more chilli.

To illustrate his point, he prepares a vindaloo, a dish loaded with chillies that he admits is entirely inauthentic ("I don't think the word vindaloo exists in the Indian dictionary") but nonetheless serves up with enthusiasm to drunk Manchester revellers. The original dish, an appetising vegetable vindaloo, he decides is not spicy enough for testing purposes; it comes back from the kitchen with a liberal sprinkling of alarmingly scarlet ground chillies on top. "Have that bit there, then you'll be sweating," he says. "If you don't you're not normal." Sure enough, within minutes the photographer and I are huuyubbing heartily. (Fisher's advice for dealing with chilli burn, incidentally, is to eat dessicated coconut. "It's a solid that is oily enough to take up and hold the capsaicin and keep it away from your mucus membranes, and has
a large surface area to absorb
the capsaicin.")

Despite my request for the hottest dish on the menu, however, Mir is anxious to stress that the flavour and enjoyment of spicy dishes is not due only to their chilli content. "Hot curry has chilli but also cloves, cardamom, cumin and nutmeg. It is these spices that really bring out the aroma and taste. If you use chilli in too great a quantity it just burns and it spoils its taste. Chilli's hotness is different to the spicy hotness. If you put a clove in your mouth it burns, but it's a different type of burning."

Rocky Durham, executive chef at the Santa Fe restaurant chain in London and an expert in Mexican and New Mexican cuisine, is in emphatic agreement. "To talk about chillies only in terms of heat is the same as talking about wine and only mentioning the alcohol. "His favourite chilli, "this week", is the comparatively mild chipotle, "a hard wood smoked, dried jalapeno". "It's great in soups and sauces," he says. "It gives this wonderful smoky heat. There are so many ways to use chilli to explore with: some that have been smoked, some are dried, some are toasted, blackened, burned before they are used. The important thing is to get a depth of flavour into the food rather than just concentrating on the heat."

And so what future beckons for the Tezpur chilli, now officially the hottest in the world, twice as strong as its nearest rival in Mexico, the red savina Habanero (which scores 577,000 on the Scoville scale)? It seems its culinary uses are to be eclipsed by its pain-inducing properties: scientists from the local defence research laboratory in Tezpur hope to use it as the main ingredient in a new tear gas.