Fruit of their labours

How to make the perfect wild-yeast fruit beer. First, find an old, derelict brewery. Second, spill beer everywhere. Then wait, watch and enjoy

People who think they don't like beer often nonetheless enjoy the cherry, raspberry and apricot versions that have blossomed on supermarket shelves these past few years. But some purists turn up their noses at a meeting of grain, hops and fruit.

The truth is that, while some fruit beers taste like alcopops, others are as complex as pink champagne. The secret is in the building where such a beer is brewed. The atmosphere must contain an invisible life form: old, wild yeasts, which actually live and develop in the breweries over the years. Until recently, such "ghosts" have survived only in a handful of breweries in the Zenne Valley, near Brussels. Now, they have taken up residence in Britain, in the historic town of Stamford, Lincolnshire, at the Melbourn Brothers brewery.

On the whole, these ghosts prefer very old breweries. This one, next to All Saints' Church, stands on a site where beer may have been made in the 1200s, when the town had three friaries and many visiting wool and grain merchants from Flanders. There was certainly an ale house on the site in the 1600s, and some of the buildings clearly pre-date the early 1800s, when the present brewery was built.

The brewery closed in 1974, when its steam boiler was deemed dangerous. Subsequently, the brewery's tied pubs were for a time supplied with beer by Samuel Smith's, of Yorkshire. That arrangement has long expired, but the Yorkshire company has quietly tended and restored the brewery.

Now, with a new boiler, it is sporadically working again. It is an extraordinary experience to see the steam firing life into the 6ft high, 12-horsepower engine that drives the brewery. The iron casings of the engine, immaculately painted in fairground green and red, resound to the thump of its single cylinder until its 3ft flywheel whirs into a blur. The belt- drive to a system of pulley wheels is engaged, and the brewery's grain mill vibrates into action. In a brewery of this vintage, it is possible to see such a process for what it is: a combination of agricultural industry and cooking.

Each activity is on a different floor, so that the grains and water, and the brew, can flow by gravity. The malt is stored in the loft, the mill is on the next floor, the mash-tun, the vessel in which the mash of raw ingredients is mixed, below, then the kettle, the fermentation and maturation cellars and the boilerhouse.

As the three brewers scurry from one level to another, adjusting controls, it is impossible to escape the conclusion that they are enjoying themselves. They sweat and swear, but see and smell the grains, water and hops being transformed into beer. It is rather more sensuous than sitting at a computer watching it all happen on a screen.

The sexiest part is the awakening of the ghost. The idea is to match the style of beer made by the breweries of the Zenne Valley. In countryside much painted by Bruegel, they have persisted with the medieval technique of brewing with the wild yeasts already present in the atmosphere. In these breweries, after the boil, the brew is cooled in an open vessel, into which the wild, airborne yeasts can descend. The breweries themselves are also left relatively uncleaned, so as not to disturb resident yeasts. More wild yeasts live in the fermenters, which are made of wood rather than modern steel.

This type of beer is known as Lambic, probably after the town of Lembeek, in the Valley. Some of the wild yeasts are so distinctive as to have local names such as Brettanomyces Lambicus and Bruxelliensis. Others resemble those used to ferment fino sherry, adding a further allusion of flavour.

Lambic beers are an acquired taste; are costly because they take years to ferment; and require a brewery with plenty of nooks and crannies to accommodate wild yeasts. Nor can any other style of beer be made in such a brewery: the resident wild yeasts would turn it sour. So why take the trouble? Because these beers, a taste of brewing history, have a connoisseur following. And because their tartness is the perfect foil for local fruits in the Valley, such as cherries.

A friendly Lambic brewery supplied a quantity of fermenting beer to Melbourn a few years ago. Some was allowed to reside in Melbourn's swamp-cedar tanks for a period of maturation, but much of it was hosed around the brewery. The idea was to impregnate the Belgian wild yeasts into the fabric of the steamy old premises. Melbourn has since made three brews of its own, fermented with the newly resident yeasts. Every few months, some of this beer has been sprayed around, building up the organisms. This practice is completely unknown in conventional brewing.

The first beer to be brewed at Melbourn, with the further addition of strawberries and apricots, in the form of both whole fruit and juice, is now available in some of the fancier wine merchants. Melbourn Brothers Strawberry Beer seems dry and almost medicinal in the nose, but balances its obvious graininess with a clean, fruity sweetness and a perfumy finish. The Melbourn's apricot version is crisper - and expresses robustly that interplay of sweetness and winey sournes

Melbourn Bros fruit beers are available nationwide from mid-June at Waitrose supermarkets, and from good independent retailers including: Chatsworth Farm Shop, Pilsley, Bakewell, Derbyshire (01246 583392, mail order is also available); County Stores, 52 North Street, Taunton, Somerset (01823 272235); Larners of Holt, 10-12 Market Place, Holt, Norfolk (01263 712323); Peckham & Rye, 21 Clarence Drive, Glasgow (0141 334 4312), 155- 159 Bruntsfield Place, Edinburgh (0131 229 7054), Unit 11, Main Hall, Waverley Station, Edinburgh (0131 557 9050); Winchcombe Wines, Wichcombe, Glos (01242 604313).