Yoshihiro Murata is holding up a length of kombu, a dried seaweed. The Japanese chef is explaining how he makes dashi, the stock at the heart of Japanese cuisine. His audience, mostly top British chefs, is gripped. Dashi, you see, unlocks the key to umami - the “fifth taste” after sweet, sour, salt and bitter.

We are attending the grandly named umami summit on Piccadilly, London. Its aim is to show off dashi and umami, to explain how they are used to create low-fat dishes, and to mark the launch of a book, Dashi and Umami, which includes a foreword by Heston Blumenthal.

It's not only Japanese chefs who work with umami (a word derived from the Japanese for “delicious”). Blumenthal and others have been employing the principle for years, and now a good number of chefs use it to enhance and balance their dishes.

Today's delegate line-up includes Claude Bosi, of Hibiscus in London (two Michelin stars), Andrew Fairlie, of Gleneagles, Sat Bains, from Nottingham, and Pascal Aussignac, of Club Gascon (all with a Michelin star each).

Similar summits have taken place in San Francisco, New York and Kyoto, where restaurants use dashi the most. Bosi was also at the Kyoto event in December. He made cheese on toast using Worcestershire sauce to demonstrate umami-rich ingredients British-style to Japanese attendees; while Bains produced pork belly with Marmite for a similar umami hit.

The trip influenced Bains so much, he says, that he has adapted the style of his cooking - one of his new dishes is beef cheeks cooked with seaweed, onion, yuzu fruit and soy. “I use less salt now and my flavours are much cleaner - it's like starting from scratch,” he admits.

Bosi was similarly impressed and his menu now features dishes such as tartare of mackerel with ox cheeks, purée of sesame seed and dried bonito. “I was aware of the word umami before the trip but I didn't really understand it,” he says. The simplest explanation? “It makes your mouth water.”

Isolated as a specific taste in 1908 by a Japanese scientist, Kikunae Ikeda, umami is the savoury taste imparted by glutamate and five ribonucleotides, including inosinate and guanylate, which occur naturally in many foods, including meat, fish, vegetables and dairy products. To your man in the (Japanese) street, it is the “yum factor”.

A hush has descended as four of Japan's finest kaiseki (traditional multi-course cuisine) chefs take their places in front of the podium. Frantic bowing is followed by a solemn introduction from the Umami Information Service, the event organisers.

Murata, the keynote speaker, is the owner of Kikunoi in Kyoto, renowned for its mastery of kaiseki. “Did you know that human breast milk contains high levels of umami?” he asks with a grin, as he puts the kombu on to simmer. Everyone laughs.

The boys from The Fat Duck - which reopened yesterday after a mystery food-poisoning scare - are here. They are working on a few umami projects, including cooking spaghetti bolognese (a umami-rich dish) in six different ways with a little help from lab rats at Reading University. But not every dish at Blumenthal's restaurant must be packed with umami. “It's all about balance,” says The Fat Duck's development chef, Kyle Connaughton. “You take the diner on a journey - an all-umami menu would be too overpowering.”

Take their now legendary “sound of the sea” dish, where diners listen to the sound of crashing waves on an iPod as they eat - a course midway through the meal provides the first big umami hit. Shellfish is cooked in a kombu extraction, and powdered kombu is used in the “sand” (the dish resembles a shoreline complete with foamy waves), along with ground-up dried fish and plenty of miso (a traditional thick paste).

Our mouths are beginning to water now. We have just tasted that kombu simmered in soft water for 30 minutes (it has to be soft water, the Japanese chefs tell us - they use Volvic while they are here). It is savoury and slightly salty, even a bit fishy. Not unpleasant. But umami? We are not sure.

Then we try it with honkarebushi (bonito) shavings, which are strained off as soon as they have sunk to the bottom of the pan. This is known as ichiban dashi. There are many recipes for dashi - each restaurant has its own method - but ichiban and niban dashi are the most commonly used. The flavour is much more intense: I let out an involuntary “yum”. “Who recognises umami now?” asks Murata. Almost everybody present raises a hand.

“It stimulates part of the brain that indicates pleasure,” explains Murata. “You want to eat more and more.”

Next it is Kunio Tokuoka's turn on the podium. The pioneering head chef of Kitcho Arashiyama, in Kyoto, is explaining how we taste. “We have 380 different smell receptors in the brain, and 50 that detect bitterness alone on the palate. Our temperature and consistency receptors are innumerable,” he says. “It is possible to increase the umami level in a dish simply by adding bitterness, aroma and texture. Umami is not just about deliciousness. It's a complex thing and you have to find your own way of increasing it.”

Tokuoka is blinding us with science, but we understand why we licked our lips more after trying the bonito-infused dashi - the umami is heightened when inosinates are combined with glutamates. The bonito is packed with the former, while the seaweed is pure glutamate.

“By increasing umami in food you can reduce the amount of cream, butter and oil,” says Tokuoka, adding that a kaiseki meal gives you the same satisfaction as an equivalent European meal but with only half the calories.

But if you don't have much (or any) dried fish or kombu in your pantry, are there other ways in which to boost umami levels? Answer: yes, plenty.

Parmesan cheese is second only to kombu for chalking up the glutamates and high umami levels can be found in dozens of ingredients, from tomatoes and cured ham to mushrooms. At the very least, we should always choose a cheeseburger over a regular hamburger. Getting it yet?

www.umamiinfo.com

Ten umami-rich foods

Tomatoes (particularly sun-dried and ketchup)

Wild mushrooms (dried shiitake)

Rich bouillons

Cured and smoked meats

Cheese (particularly Parmesan and ripe blue cheeses)

Fish and shellfish (particularly anchovies and tuna)

Seaweed

Soy sauce

Oriental fish sauces

Saké

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