Imagine being given a bowl of stew made from a two-week old turkey carcass, half a can of mushroom soup, droopy vegetables scraped from the back of the fridge and half a leftover apple pie. Known as 'Everything Stew', the dish was regularly served at Ruth Reichl's New York, Jewish family home by her manic depressive mother who had unusual taste buds and couldn't resist a food bargain - even if it was buried under a crust of mould. Reichl's mother's food was dangerous (she once catered for a party after which 26 guests had to have their stomachs pumped) so, early in childhood, Ruth felt obliged 'to keep Mom from killing anybody who came to dinner'. That mission stuck and widened in scope. Realising that 'discovering food could be a way of making sense of the world' she started to investigate the psychology and politics of food. Reichl soon became a compulsive and terrific cook and later decided to protect the public from unsound meals by writing candid restaurant reviews.

At 53 she has written two food-fixated memoirs and is now editor of Gourmet magazine. Americans celebrate her as the goddess of good food, but in her days as a restaurant reviewer for the New York Times Reichl was forced to keep a low profile. Most British food critics make little effort to go undercover at restaurants and many openly mix with chefs and restaurateurs. Their American counterparts are a tough breed, operating as anonymous food sleuths and Reichl, who has a reputation for writing the fairest reviews possible, went to absurd lengths to protect her identity. Her wardrobe was home to 12 different wigs and outfits to furnish the 12 different personalities she adopted. Each evening she spent hours disguising her frizzy hair, climbing out of her floppy ethnic clothes and perfecting a mask of make-up. 'Chloe' was her favourite and must have required a lot of effort to pull off: a blond bombshell in black satin, spiked heels and an inch of make-up. Chloe was said to stop traffic.

Reichl became a national enigma, epitomised in a Richard Avedon photograph where she posed with two cellophane-wrapped chefs and a napkin over her head. Waiters were offered cash if they spotted her, Reichl's photo was stuck to restaurant kitchen walls, and her credit card number - which she changed every six weeks - was faxed from restaurant to restaurant.

But she was rarely caught, and it is no wonder that as I walk up to her office in the Condé Nast building in New York's Times Square, I expect to be meeting a schizophrenic or, at the very least, a shady figure. I make my way along corridors of blank, important looking doors toÊthe the echo of clicking heels and wafts of DKNY perfume and into Reichl's surprisingly human office, where a friendly looking woman stands, smiling under an unruly bundle of hair, and says 'Shall we go to lunch then?'

This woman was a professional eater. In her years as a restaurant critic at the LA Times and New York Times she packed in 10-12 restaurants a week. She knows where to find the best food in New York, so I follow her across Times Square to her to one of her favourites, Esca. My rumbling tummy competing with the roaring traffic.

Once we reach the restaurant I expect a spotlight to pick her out and the waiters to launch into a full-blown rendition of 'Hello Ruthy'. Luckily Esca is a modest restaurant and our reception is less dramatic. Just as we sit down, the head chef arrives to receive Reichl and tell us with his thick and low Bronx accent what great Alaskan crab he has on today. 'I'll make something special up for you two'. We both concur. 'Isn't he great?' Reichl enthuses, and with a hint of adolescent awe adds, 'He's so unpretentious.' The food, when it appears, is simple and uncluttered.

'I like food that tastes of itself. My food tastes came out of the whole Californian cuisine movement in the Seventies, which questioned where food came from and how it is produced. The movement was about making relationships with farmers, getting these really great products and pretty much leaving them alone. Left to my own devices my ideal meal would be a perfect peach just by itself.'

Through the Seventies and into the early Eighties Reichl lived in a self-sufficient commune in Berkeley with her first husband, the artist Douglas Hollis. She cooked food packed with nutrients but low on glamour, and for a brief period she found herself concocting edible dishes out of food retrieved from the local dumpster. Her days were spent working as a chef in a collectively run restaurant and doing bits of journalism. When she was asked to write and eat -Êdoing restaurant reviews for a local publication, New West magazine - the offer was impossible to resist. 'I'd get up in the morning and eat millet, take out the garbage and then go off to some fancy hotel and be wined and dined.'

Reichl had to put up with a lot of finger wagging from her anti-establishment flat-mates: 'There was a lot of guilt and if I didn't feel it, everybody made sure that I did. It had been our choice to live poor but I was out there in my studio working while everybody else was sort of sitting around drinking wine and having political discussions.'

Food arrives at our table - not food we have asked for, but a small appetiser with the compliments of the house. Now that Reichl can eat openly in restaurants this sort of treatment is commonplace. We dig in and discuss the importance of food. She deliberates over whether food is an art and concludes, without certainty, that because it is sensual and not intellectual food is never art, she thinks. However, she is certain that food is about more than flavour and indulgence.

Reading her memoirs, Tender at the Bone, and her second volume, Comfort Me with Apples (out next month), it is clear that Reichl's thoughts and experiences are processed through her interaction with food. Memories of meals, smells and flavours describe significant places, people and emotions, and the books are punctuated with personal recipes.

One section of her new book is dedicated to the break-up of her marriage and the beginning of her relationship with her present husband, Michael Singer. She had been having an affair with him for some time and Doug had been seeing other women. 'In the context of the time the affairs really weren't such a big deal. It was pre-Aids,' Reichl says, but then retreats slightly adding, 'Well, it wasn't such a big deal to him, it was to me because I'm such a good little girl.' Reichl had piles of journals from the time: 'There was all this emotional feeling and I kept rewriting it and none of it was working. One morning I just threw it all out and moved through the events very quickly, using recipes at the end of each chapter.'

Food holds a particular emotional charge for Reichl (she is obviously thrilled by today's fresh Alaskan crab, served plain). Although she says she is 'not big on privacy' and both her books are open about her affairs - most notably with Colman Andrews, former editor of New West magazine (he is now a friend and rival editor at Saveur) - her writing gives little away and her recipes are consciously used in place of emotive description.

'You're going to write this momentous thing about splitting up from your first real love,' she says tearing bits of crab meat from the shell, 'and you could be squirming over it the rest of your life. My editor really wanted to know what I was thinking but I wanted to erase the marks of writing. When you are very emotional, you have all this flowery language. After September 11 every writer wanted to talk about their feelings and I did it too in an editor's letter, but really it's easy to sound profound.'

Reichl separated from Doug and married Michael, an investigative journalist who was unofficially assigned by Reichl the unenviable task of accompanying her to restaurants all over California, all expenses paid. Michael was the Joe Blow of eating out, with a palate that craved for basic dishes and didn't see the value of food tweaked into art. Reichl morphed him into a much loved character in her columns called The Reluctant Gourmet; 'That worked really well for me because he was invented at the time in the early Eighties, when the American food movement was beginning and became very pretentious. Michael got to say all the things that, as a critic, I couldn't say. He got to point out how ridiculous it all was.'

Reichl was the precursor of a new breed of American restaurant writers who sided with the customer and didn't focus solely on the food, trying to capture the whole dining experience. 'It is my firm belief that nobody goes out to eat. People go out for all kinds of reasons - food is just one of them,' says Reichl as the chef comes back to check if we like the crab. I nod but Reichl goes into critic mode and comments that there wasn't enough meat on it. The chef doesn't flinch, but leaves us to eat.

Many conservative foodies were shocked by her approach. The established New York restaurant Le Cirque was famously embarrassed when Reichl exposed the disparity between the treatment she was given once they had recognised her. Her second review for the New York Times in 1993 was criticised by many Francophile traditionalists like her predecessor Bryan Miller because she gave three stars out of four to a SoHo Japanese restaurant - unheard of up until that point in New York. Miller objected: 'How do you think she comes off giving a SoHo noodle shop three stars? She has destroyed the system that ... I upheld.' Reichl laughs remembering this, 'This place is hardly a little noodle joint'. It didn't take long for her style and diligence (she often visited restaurants nine times before reviewing it) to win New Yorkers' trust.

While Reichl was busy revolutionising food writing, Gourmet - the 60-year-old glossy magazine once known for it's innovative writing - was sitting on shelf racks gathering dust. It had a reputation for being staid and exclusive and, in 1999, Reichl was brought in to make changes. Despite her reservations about fine dining she accepted the job. One strong appeal was that it allowed her to eat dinner with her and Michael's only child Nick - 'I think family meal times are very important' she reflects. She is relieved to get back to cooking, though tonight's meal is simple: Bolognese left over from the weekend.

She was given free rein over Gourmet. Reichl brought in strong, varied writers and made food more accessible to the public by adding manageable recipes and useful information. She also made Gourmet a forum to discuss the political issues of food. Sales have rocketed.

Another complimentary offering arrives - this time a dessert. Reichl looks anxious and confides, 'I'm not a desserty'. A bite of her panacotta is enough and she begs 'taste some, I don't want it, I really can't'. She doesn't want to offend the chef, so I eat my chocolate pudding and try to squeeze hers in. We leave and walk back through Times Square. A pro at picking her way around food, Reichl is ready for work. I feel like a Cherokee jeep has parked in my stomach and am ready for bed.

To order a copy of Tender at the Bone for £6.99 with free UK p&p or Comfort Me With Apples for £10.99 plus p&p (rrp £12.99, out 6 June)call the Observer book service on 0870 066 7989

Ruth Reichl's favourite restaurants

Chez Panisse, Berkeley

If there were only one place I could eat for the rest of my life, this would be it. The food is local, organic and utterly inventive. The menu changes every day, there is just one meal.

Ginza Sushiko, Los Angeles

A sushi bar run by a true artist who makes his own plates and flies to Tokyo once a week in fugu (blowfish) season to bring back his fish.

Duomo, Taormina, Sicily

The food is very simple and very good. Endless sea urchins, blue fish with blood oranges, great greens.

Pierre Gangniere, Paris

The ultimate three-star restaurant, run by an intellectually daring chef who walks a tightrope every night, inventing new dishes that might not work but somehow always do.

CDMC Seafood Centre, Singapore

A bunch of little shacks serving seafood on the beach outside of Singapore on East Coast Parkway.