Steven Kaplan, an American no less, is weaning the French off the travesty of a baguette they have eaten since 1945. John Lichfield reports

You have to be a brave man to mess with a national symbol, especially someone else's national symbol. Steven Kaplan is not just brave, he is heroic. This week, Kaplan - a non-Frenchman and, even more heroically, an American - will publish the first gourmet guide to the baguettes of Paris.

In Britain, the cliché Frenchman is a grumpy man wearing a beret, gripping a baguette under his arm. In France, the cliché Englishman is a mild man in a bowler with an umbrella over his arm. Like the bowler, the beret has become virtually extinct. The baguette, however, thrives. Or does it? Anywhere in France - and in any pseudo-French baker in the world - you can buy long tubes of fluffy, ultra-white dough, which will set into blocks of teak within half a day. The world - including France - calls this a baguette or typical "French loaf".

Kaplan, the Goldwin Smith professor of European history at Cornell, and one of the foremost authorities on the history of bread, calls it something else: "an impostor, an interloper, a tasteless, aroma-less monstrosity, which has existed for only half a century".

The real French baguette, whose history Kaplan has traced back to the 17th century, began to disappear after the Second World War. Bakers, even small, artisanal bakers, started to adopt modern methods and short-cuts which spawned feather-light, lily-white loaves. The French were delighted. After the dark, lumpy, indigestible, war-time bread made under German occupation - which came to be known as pain caca or "poo-poo bread" - the whiter-than-white loaf was a symbol of liberation, peace and modernity.

By the 1980s, the pre-war baguette - made from double-fermented dough, with no artificial yeast and no chemical additives - had almost gone the way of berets, yellow cigarettes and other French exceptions. It took a campaign by Real Bread enthusiasts, including Kaplan, to prod the French government into promoting a retro-baguette revival. In six out of 10 Paris bakeries, far fewer in the provinces, the light, white "baguette courante" or "standard baguette" is now sold alongside the succulent, longer-lasting, creamy-coloured, crunchy, taste-filled baguettes which existed in France before the Second World War. It is this baguette - the "baguette de tradition" or "pain de tradition", as defined rigorously by law in France since 1993 - which is the principal subject of Kaplan's book Cherchez le Pain.

Kaplan, 60, who spends half the year in the French capital and half at Cornell University in the US, has eaten his way in the past eight months through 637 of Paris's 1,240 small bakeries. That averages more than four bakeries * a day - against all expectations, he remains a very trim man. After careful consideration of appearance, smell and taste of crumb and crust, he has chosen the 100 best baguette bakeries of the French capital. He has awarded, Michelin-like, three wheat-sheaves to the best dozen; two wheat-sheaves to another 18; and one wheatsheaf to the rest. Parisian bakers await his book with barely suppressed excitement and foreboding. Kaplan is not just a mere American, and not just an academic expert: he is an enthusiast, a connoisseur, a cheerleader for bread, a man who trained as a baker and worked in bakeries, a man whose researches and opinions are respected, even feared, throughout the French bread-making world.

His conclusions? "The bad news is that half of small bakeries in Paris are producing baguettes de tradition which are, quite frankly, awful. The good news is that even these bad, traditional baguettes are a hundred times better than standard, white baguettes."

Kaplan, who has published four previous books on bread-making and the history of bread, judges baguettes in three ways: aspect, aroma and taste. A good, traditional baguette should look lumpy and individual, not uniform, he says. Inside, there should be a jumble of uneven apertures in the bread, not a standard pattern of holes. "Smelling the bread, I want my nose to be assaulted by a wide variety of aromas. If I don't get a rich array of aromas - aroma is an important component in taste; and our memory of smells creates a large part of our pleasure in food - I know that this is a mediocre baguette."

The taste of a good baguette should be a balance of sweet and sour, he says. It should "both linger and alter in the mouth"; the crust should "crunch under the tooth"; the crumb should be moelleux. Kaplan, who is married to a French woman and speaks fluent French, often resorts to French words to describe bread. The wonderfully evocative word moelleux has no easy English translation; it means, roughly speaking, moist, soft and velvety.

Trying to invent a language in which to describe bread is part of Kaplan's motivation for writing the book. "We have a vocabulary for wine but not for bread, which is just as, if not a more important, part of our civilisation. I wanted to try to create a vocabulary for bread which would be supple, flexible and not too pompous." His other motivation is to celebrate, and encourage, the revival of the old-style baguette, which is still a rarety in some parts of France. In the general run of Parisian bakeries, the "baguette de tradition", which costs around €1 (66p), now represents 18 per cent of the turnover in baguettes. In other words, the fluffy, tasteless, white baguette, which costs around 70 euro cents (46p), and its bigger sister, the "pain", still rule the French table.

With all modesty - "you have to be careful as an American telling the French what they should eat" - Kaplan hopes his book will lay a trail of crumbs to lead Parisians back on to the path of the true taste of French bread.

Nowhere is his book awaited with more anxiety than on the rue Monge in the fifth arrondissement, on the Left Bank of the city, where two of the capital's best, small bakers - Eric Kayser and Dominique Saibron - do business at opposite ends of the street. One calls his version of the "baguette de tradition", "Le Monge"; the other calls his loaf the "Baguette de la boulangerie de Monge". "They are bitter rivals," Kaplan says. "They absolutely hate each other but both make superb baguettes."

He prefers not to divulge, pre-publication, the names all of the inaugural "three wheatsheaves" winners, which may eventually become as prized as three Michelin stars. However, The Independent on Sunday can reveal that - luckily for civil peace in the fifth arrondissement - the deadly rivals of the Rue Monge are both named among the baguette elite.

The toast of Paris

Le Boulanger de Monge (pictured) 123 rue Monge, 75005, tel: 00 331 43 37 54 20 The toasty caramelised flavour of the crust complements the fruity crumb

Jean-Noel Julien 75 rue Saint-Honoré, 75001, tel: 00 331 42 36 24 83 The crust dominates the crumb, giving a rich and almost sweet taste and a buttery aroma

Fabrice Cléret 10 Place des Petits Pères, 75002, tel: 00 331 42 60 90 23 This baguette emits a floral aroma and offers a voluptuously rich taste

Eric Kayser 8 rue Monge, 75005, tel: 00 331 44 07 01 42 The 'baguette Monge' boasts a handsome architecture and a spiced-buttery and nutty flavour

Jean-Luc Poujauran 20 rue Jean-Nicot, 75007, tel: 00 331 47 05 80 88 Try his 'country flute' - a delicious thick crust, a flavour of dried fruit and a spicy aroma

Thierry Meunier 29 rue Tristan Tzara, 75018, tel: 00 331 40 38 18 98 The Meunier baguette boasts a muscular crust and a taste of crushed cereal infused with creamy butter

'Cherchez le Pain: The Guide to the Best Bakers of Paris' by Steven Kaplan is published by Plon-Perrin, priced €15 (around £10)