REASONS TO BUY a copy of Patricia Unterman's San Francisco Food Lover's Guide (Ten Speed, $18.95), updated after six years, should probably not include the expectation that the new edition leaves the earlier one (actually ones, since the 1997 version was an update of the original 1995 guide) irrelevant. Because it doesn't: There is plenty of overlap, and despite the rise-and-fall tumult of recent years, most of the places Unterman found worthy of mention in 1997 are still around – and are mentioned again in 2003, often in the same language. The entry for Postrio, for instance, is identical, and not quite flattering, in both volumes, leading one to suspect that Unterman's intelligence on that restaurant, at least, isn't as fresh as it might be.

But then the book lays no claim to omniscience, which in any case is not possible in a food culture as vast and varied and variable as northern California's. Unterman is after all a first-rate food critic (a surprisingly underrepresented species here) who understands that criticism is always personal and impressionistic and fragile; too much plodding method and the magic collapses, too little and one is left with narcissistic gibberish. Balance, then. We have long trusted her because she understands that balance, and because she trusts her own passion for food and is willing to be led by her curiosity into new restaurants and realms of ingredients and recipes.

The recipes, incidentally, appear to be the part of the book that's been subject to the most revision. About half of them are new. Meanwhile there is commentary on a host of restaurants that have opened since the last edition of the book appeared, although it is an odd experience to leaf through the pages on the Mission (the book is organized by neighborhood) and find oneself reading about Butterfly or Foreign Cinema, a pair of dot-com stars that survived, or perhaps I should say are surviving, the crash. They are old news, but on the other hand it is important to be reminded from time to time that some dot-com era restaurants were actually good.

It should come as no surprise that Unterman – owner of the seafood restaurant Hayes Street Grill – is tuned in to the sustainable-fishing question. The earlier edition of the book contained a big chart on the seasonal availability of local seafood; the new edition reproduces the chart while emphasizing the need to choose seafood that isn't subject to overfishing or produced through ecologically damaging methods.

The emphasizing is done clearly but with grace – one of Unterman's gifts to us, just as her revised book will no doubt be a gift from many of us.