All hands to the pump: Cockermouth's historic Jennings brewery is back in business

There's white smoke coming out of the chimney," Jeremy Pettman says with a relieved smile. Cumbria hasn't chosen a pope: the smoke signals that Jennings Brewery is back in business and that head brewer Pettman has started the first brew of Jennings Bitter since the disaster.

Back in November, Jennings' home town of Cockermouth was hit by devastating floods. Homes and shops were ruined and vital bridges over the rivers Cocker and Derwent were swept away. The brewery, on its site at the foot of Cockermouth Castle since 1878, was especially badly hit as it stands at the confluence of the two rivers.

Brewery manager Gaynor Green points to a line on a newly whitewashed ground-floor wall that marks the height the water reached on 19 November: six feet, or two metres. She recalls arriving at the brewery to find the ground floor, including the visitor centre, knee-deep in water. By the time she had evacuated the entire staff a few hours later, the water was waist-high and vehicles in the car park alongside the rivers were bobbing around like corks.

As well as the visitor centre, the cooperage, the yeast store and the power system were destroyed. The mash tun and coppers are located one floor up and were saved, but 50 tonnes of malted barley had turned to concrete in the malt store. Casks of beer floated out of the brewery and ended up in Workington (which may have brought some relief to that stricken town). Without power, malt and yeast, the brewery was at a standstill.

Once the waters had receded, Gaynor Green called the workforce together and told them there was no question of Jennings closing for good. She had received a phone call from Stephen Oliver, boss of Marston's Brewing Company, which owns Jennings, assuring her the brewery would re-open and asking her just one vital question: "Do you want to brew beer off-site, or wait until the brewery opens again?" Green says she was nervous about brewing Jennings beers elsewhere. But if the closure was going to last for a month or more she would need supplies for pubs in Cumbria as well as for bottling. Richard Westwood, Marston's director of brewing, arrived two days after the flood, surveyed the damage and told Green he could arrange to have the Jennings beers – Bitter, Cumberland Ale, Cocker Hoop and Sneck Lifter – produced by Banks's in Wolverhampton and Marston's in Burton-on-Trent.

There was no attempt to pass the beers off as genuine Jennings brews. Special attachments, known as "wobblers", were clipped to hand pumps in pubs to explain why the beers were being brewed elsewhere and that 10 pence from every pint sold would go to the flood relief fund. Sales of beer have so far raised £178,000 and make up the biggest single contribution to the fund.

"We've had no negative reaction to the beers," Gaynor Green says. "Customers said they didn't taste the same as when they were brewed in Cockermouth – and that was music to my ears, proving that cask beers have a unique taste due to their location." Sneck Lifter, a dark Porter-style beer named after the catch, or "sneck", on a Cumbrian pub door, was brewed at Marston's and had the famous sulphury aroma from the Burton water, which is never encountered in the Cockermouth version.

Green has nothing but praise for her workforce. "They came in their wellies and old clothes and cleaned the brewery up," she recalls. "BT fixed the phone lines within a week so the telephone sales girls could start moving beer again." There was sufficient stock in the system to enable Jennings to supply its customers until new beer was ready. A container-load of beer destined for bottling was retrieved and racked into casks for pubs. The mash tun and coppers were not damaged and the fermenters were cleaned of ruined beer, but production couldn't start again until the buildings were dry and passed as safe.

Environmental health officials insisted that brewing water from the on-site bore hole had to be cleaned out three times before they would allow it be used. The power panels have been moved from the ground floor to the first and should be safe even if the Cocker and the Derwent flood again.

Beer can't be made without yeast. A batch of every British brewery's yeast culture is securely stored at the National Yeast Bank in Norwich. A sample was taken to Marston's laboratory in Burton and a sufficiently large batch was made to start the first few brews at Cockermouth.

Jennings is a sizeable brewery, able to produce 50,000 barrels a year. It supplies 50 of its own pubs in Cumbria as well as other pubs in the Marston's chain in the North-east, Lancashire and Yorkshire, plus a large free trade and a growing bottling business. Marston's could have closed the site but instead has spent a large sum getting it going again. The company won't give a precise figure as insurance is still being negotiated but we're talking of a six-figure sum.

Jeremy Pettman and his deputy head brewer Rebecca Adams believe in using the finest raw materials for their beers. Maris Otter is their choice of malting barley, a variety favoured by many craft breweries because of its rich biscuity flavour and its harmony with yeast. Maris Otter was de-listed by seed merchants and agribusiness more than a decade ago and replaced with "higher yielding" varieties that produce more grain per acre. But a few specialist malting companies, such as Warminster Maltings in Wiltshire, buy Maris Otter from selected farmers and supply craft brewers.

The blend of grain for the first batch of Jennings Bitter was pale, amber, crystal and chocolate malts: it's an unusually dark version of bitter, one that has been satisfying Cumbrian drinkers since Victorian times. The colour of the malt depends on the roasting temperature in the maltings: highly roasted grain such as chocolate malt looks like coffee beans and adds a delicious dry, chocolatey note to the beer.

In the brewhouse, Jeremy Pettman mixes the malts with pure hot "liquor" – brewing water – in the mash tun. A superb aroma reminiscent of freshly baked bread and Ovaltine fills the air as starch in the grain begins its magical transformation into fermentable sugar. Two hours later, Pettman and his assistant brewer Eldred Burns taste the "first runnings" from the mash tun. The liquid is hot, biscuity, delicious and surprisingly dry rather than sweet. They are satisfied with the result and open the slotted base of the tun to allow the extract, known as "wort", to run into a receiving vessel, and then on to the copper for the boil with hops.

Jennings uses whole flower hops rather than compressed pellets or extract. Pettman believes the herbs in their natural state deliver the finest aroma and bitterness to his beers. For Jennings Bitter, he uses three English varieties, Challenger, Fuggles and Goldings, chosen for their different levels of bitterness and piney, citrus and spicy flavours. Hops are added three times during the copper boil as some of the aroma – known as the "angels' share" – is distilled into the atmosphere.

An hour-and-a-half later, the "hopped wort" will be cooled then pumped to fermenting vessels, where it's vigorously mixed with yeast. Fermentation creates so much excess yeast that Jennings will soon have enough to brew its full range of beers. One week after the first mash, Jenning's Bitter will be on its way to local pubs, helping to bring pleasure back to a community still struggling in the aftermath of the torrential floods.

Roger Protz writes beer-pages.com

Perfect partners: The best beers for food

Real ale, a living beer that continues to improve and mature in the cask, is a good companion at the dining table. Jenning's beers, malty, fruity and hoppy, match a variety of foods.

Jennings Bitter (3.5%) goes well with hearty meat or vegetable soups. It's the perfect companion for the classic Cumberland sausage, the spicy hops melding with the meat. For non- carnivores, cross the Scottish border for a vegetarian haggis.

Cumberland Ale (4%) is a bronze-coloured beer with a powerful citrus note from the hops, along with juicy malt. Drink with pasta dishes, white meat or fish. It can be used in the classic beer dish, carbonnade of beef. It is excellent with cheese, especially tangy mature Cheddar or Stilton.

Cocker Hoop (4.6%) is a golden ale brewed with Styrian Goldings hops from Slovenia. They bring a floral, resinous and piney note to the beer. This is the beer for pizza, a tangy salad, light fish or chicken.

Sneck Lifter (5.1%) is a porter, the junior version of stout. The Irish drink stout with oysters and have annual stout and oyster festivals. Sneck is therefore ideal for shellfish, but its roasted grain and chocolatey notes also makes it a good dessert beer with rich puddings or chocolate dishes.