The indigenous brew of Britain received its first recorded slur in Roman times, when the Emperor Julian composed a poem attacking an alcoholic beverage called "curmi." The exact nature of the drink is lost to history, but what is known is that the invading legions spurned it in favor of the wine they brought. Eventually they withdrew, leaving the natives to become among the finest beermakers in the world.

To say that English beer is an acquired taste is only half of it, the other half being the merry experience of imbibing the drink. Real ale, as beer brewed the old-fashioned way is now called, has had a renaissance in the past decade, and there are now a seemingly infinite variety of delicious brews to practice on, including the rich and fruity Samuel Smith's from Yorkshire, the exceptionally smooth Burton bitter from the Midlands and the clean and tangy Young's bitter brewed in south London.

The diversity is astounding: There are now 250 breweries in Britain, of which about 100 are tiny operations that have begun in the past few years. The Burton Bridge brewery, for example, opened recently on the site of an 18th-century brewery house in Burton-upon-Trent, a town renowned for its mineral-rich waters that are reputed to produce the best beers in the country. The brewery last year won top honors for its Bridge Bitter in a national beer-tasting competition, yet it is so small that the beer is distributed within an area of only 30 miles in radius.

With so many beers to choose from, it is no wonder the beer drinker's yardstick of taste develops into a kind of personal mythology. A friend from the North of England talks of discovering a beer called Gales HSB one summer on the South Coast as if dreamily recalling a first love. Another friend from London who spent a year in Wales will earnestly argue that the head-thumping Brain SA of Cardiff is a sort of happy revenge of that land's Celtic gods, turning those who drink it into poets and pub brawlers before inducing a long and dreamless sleep.

Fortunately for travelers whose time may be limited, London is a mecca for regional beers and they can taste a wide selection without ever leaving the West End (even if a pint in London is about 10 pence more expensive than in the country). Most pubs are tied houses, which means that they are owned by one brewery and therefore sell only their own real ale. Free houses are independently operated and typically offer real ales from two, three or more breweries.

Pontefract Castle, on Wigmore Street two blocks north of Bond Street station, is a free house that has half a dozen traditional beers on tap. The Sun, a bright and friendly pub on Lamb's Conduit Street on the eastern edge of Bloomsbury, has 15 handpumps and a frequent rotation of guest beers -- one of the widest selections of real ales in London if not England.

Not surprisingly, The Sun is often crowded by mid-evening. I used to enjoy a pint of Timothy Taylor's Landlord, a bracing full-flavored brew, and then walk around the corner to North Street to bask in the funkier atmosphere of a pub called The Moon. My beer at The Moon was King & Barnes Festival, whose mellow taste seemed to complement the mood of a place where the jukebox was programmed with obscure 1950s tunes.

Although England is now a beer fancier's heaven, this is a dramatic reversal of a trend in which traditional beer nearly became extinct. By the late 1960s, the six largest brewers in Britain -- Watney, Bass, Courage, Allied, Whitbread and Scottish & Newcastle -- had consolidated their hold of the market with processed, artificially carbonated beers.

Then in 1971 the Campaign for Real Ale (CAMRA) was formed, and this most remarkable consumer movement fought and won the battle of British taste buds. Through a publicity campaign involving picketing and protests, British drinkers persuaded the Big Six that there was a market for real ale, and they began producing traditional beer in addition to the fizzy kind; smaller breweries followed suit. CAMRA members are active throughout Britain today, checking that the beer at their local pubs is up to standard. (The watch-dog group even has its own watch dog, a Great Dane named Ben who in blind tastings will unerringly drink from a doggy dish of real ale and accept no substitutes.)

What is real ale? All beermaking follows a basic recipe using malted barley, water and hops. Yeast feeds on the sugar of the malt, and the fermentation produces beer. Beers may differ in the quality and quantity of ingredients, and there are variations in the process of combining them, but what mainly distinguishes real ale is that the fermentation is carried through unmolested to the cask that arrives in the pub. The beer has a natural and soft sparkle given to it as carbon dioxide is released during fermentation, and when the beer arrives at the pub it is still "alive" and must be cared for properly and consumed within a few weeks, before it goes off.

Processed beer, on the other hand, is Dead On Arrival. It has been filtered and pasteurized, chemicals have been added and sometimes so have other ingredients such as rice or even potato starch. The beer is artificially carbonated like soda pop, and generally the resulting drink is bland and can taste slightly metallic or cardboardy. American beer has long been processed; for brewers, the method makes great sense since the beer is far easier to transport and market.

Though ale and beer are now interchangeable names, the story of English beer owes much to their historical difference. From Anglo-Saxon times until the 15th century, English monasteries brewed ale that used malt but not hops. Thereafter hops were imported from Holland, and grown in the county of Kent south of London, where they are still harvested for British brewers today.

Hops is a plant that takes no active part in fermentation, but rather adds a bitter flavor and aroma. For several centuries after its introduction a schism divided English brewing -- between the sweeter, stronger ale and the hoppy, bitter beer, which tended to be lighter but tangier. Despite the best efforts of such famed ale champions as Henry VIII, who insisted that his personal brewer make only unhopped ale, the separate styles eventually flowed together.

Even so, the variety of tastes of real ale is traceable to these once-distinct tributaries: Samuel Smith's Old Brewery Bitter, Wadsworth 6X, Everards Old Original and Abbot are noticeably maltier than such hoppy beers as Badger, Adams bitter, and Brakspear mild. Burton bitter is an example of a beer in which both properties are well-balanced.

Another legacy from the Middle Ages is the varying potency of beer. The custom of the monasteries was to brand x's on the casks to denote strength, strong ale being best for long storage. In the pubs today, real ale from one brewery will usually be available in two strengths, and often three, ranging in alcoholic content from about 3 1/2 to 7 percent.

Beer potency is typically designated ordinary for weakest, best bitter for medium strength and winter warmer for a brew with a wallop. Best bitter is the choice of many beer drinkers for the full-bodied flavor. The most-potent brews tend to be rich but heavy, and not to everyone's taste.

I once drove to the Yorkshire Dales, sampling the delicious regional beers along the route and finally arriving at a quaint country pub where the legendary Theakston's Old Peculiar was dispensed from a wood cask tatooed upon its side with admonitory x's. The syrupy concoction was as advertised: I quickly felt old and peculiar and also as if my sense of taste had been delivered a knockout punch.

Such hazards are part of the quest for the perfect pint, but tourists embarking on the road to good cheer can be assured that there are only a few caveats with which they should concern themselves. The vast majority of pubs, from elegant Edwardian saloons to the humblest working-class pub, now serve real ale, and it is simplicity itself to know which you are ordering -- traditional beer is drawn from large old-fashioned handpumps, as opposed to the small pressurized taps, which are for foreign and domestic fizzy beer.

A classic misapprehension is that the beer is "warm." Traditional beer is served at the temperature of the cellar, typically 55 to 60 degrees. The flavor of a good pint is unlocked at room temperature or slightly cooler, and further chilling would only stun the taste buds.

The Imperial pint is one-sixth larger by volume than an American pint, all the better for hoisting a few, unless you are more interested in sampling several beers, in which case you can order by the half-pint. You may want to look at your pint of beer in the light, not only because sight adds to enjoyment -- the colors vary from light caramel to golden brown to mahogany -- but also because on infrequent occasion the beer can be cloudy instead of clear. Beer can go off or be flat for any number of reasons -- because the pump lines are not clean or the cask has been improperly tapped or simply because the beer in the cask has reached the dregs and should be changed. A fresh, healthy pint will have an inviting aroma and a lively head, although the head on real ale will subside in a minute or so, unlike some artificially fizzed beers.

The color of English beer differs from the yellow of American and continental lagers because of the higher temperature at which the barley is malted. The rich black of Guinness stout derives from roasted barley. Guinness on draft is not, incidentally, a real ale, but a lovely brew nevertheless. A real-ale version of Guinness is bottled in Britain under the label "Extra Stout." (It is not exported, and neither is any other British real ale.) If you ask for the real-ale Guinness in a pub, take care that the bottle is poured gently to avoid the sediment at the bottom.

The latest trend in brewing is a return to the tradition of beer-making in pubs. The number of pubs in England offering their own house beer has increased from half a dozen in the late 1970s to nearly 70 today. In London, a string of five brewery pubs under the same management includes the Pheasant and Firkin on Goswell Road, near the Barbican Centre, where the visitor can peer through a glass section of the floor to see the small brewery and casks in the cellar below. The Orange Brewery pub on Pimlico Road, near Victoria Station, serves a pleasant beer with the unpretentious name of SW1, after the postal district.

For further help, CAMRA annually publishes a "Good Beer Guide" (available in most British bookstores) that even provides a road atlas of Britain, resembling a treasure map in the way it pinpoints favorite real ale pubs with symbols in the form of pint glasses.

Keep firmly in mind that the beer of your dreams is only the next foaming pint away, and you should easily avoid repeating the mistake the Emperor Julian made so long ago.