Special brew: One of Britain's most wanted beers is produced by novices under a London railway arch

Sometimes an overnight success can be just that. Evin O'Riordain's beers are drunk in some of London's most fashionable restaurants, ale enthusiasts the world over are desperate to get their hands on his latest batch and one of his stouts has recently been named Britain's best bottled beer. But how did he get to be the capital's most talked about brewer? A quick Google search. "I started making beer at home about two-and-a-half years ago," he says. "I taught myself to brew: it's simple. There's lots of information on the internet. Some of the information is good, some not so good."

You couldn't say the same about O'Riordain's beer. Standards are very high at The Kernel brewery in Bermondsey. Since the brewery was founded in 2009, word has gradually spread of the remarkable beers the 36-year-old Irishman and his colleagues Chrigl Luthy and Toby Munn are making in their tiny brewery tucked away under a railway arch just outside London Bridge. Restaurants such as the Michelin-starred Chez Bruce, Hawksmoor and Pied à Terre now stock his products, and beer bars such as Shoreditch's Mason and Taylor have made The Kernel the beer of choice for the capital's younger beer-lovers.

Interest in beer is booming again in London, and The Kernel is riding the crest of this wave. The capital, in the 19th century the world's greatest brewing city, was slow to join Britain's microbrewing revolution but things have changed in the past few years. London now boasts more than a dozen breweries, from an established and respected ale giant such as Fuller's to the Camden Town Brewery, set up in June last year and modelled along American craft brewery lines.

Few, though, have made quite the immediate impact that The Kernel, based close to the historic heart of London brewing in Southwark, has. The award-winning beer – an export stout, named the Society of Independent Brewers' bottled beer of 2011 last month – is one of a dizzying number of brews produced by O'Riordain. His adventurous approach – inspired by the American scene and by London's brewing past – has seen him use around 25 different varieties of hops (the plant that makes beer bitter) and 18 types of malt (the main ingredient of beer) since the brewery began.

Not that O'Riordain can pin down exactly what it is that makes his beers so good. "I don't have any other experience in any other brewery so I don't know what are the key factors in what make our beer what it is," he says. "Is it the recipe, the equipment, the fermentation, the strange ambiance that goes on in the railway arch? If we moved, it would inevitably change."

That the brewery itself is so idiosyncratic is a factor. A visit on a brewing day dispels any romantic notions about how beer is made. This is hard work in difficult conditions: the floor is sopping wet, the roof shakes every 30 seconds as a train rumbles overhead and it's cold. Brewing – as O'Riordain says – is simple, but that doesn't mean it's easy. Malt must be manhandled into the mash tun – where the brewing process begins – while cleaning the tanks requires a pair of wellies, a spade and strong arms. Beer is bottled, capped and packed by hand. O'Riordain spends 10 hours at the brewery six days a week, with emails and paperwork to be dealt with later in the evenings.

Nonetheless, it is clear how much the trio enjoy their jobs. O'Riordain's background is in food – he worked for Neal's Yard Dairy for many years and sold cheese at the nearby Borough Market – and the atmosphere at the brewery reflects this. A coffee break is the opportunity for O'Riordain to get out his Aeropress and lunchtime brings good bread, cheese and beer.

What must be particularly satisfying for O'Riordain is that so many of his most popular beers are stouts and porters, reminders of the capital's brewing past. "I never wanted to work anywhere else but London," he says. "All of the dark beers we make are London-inspired. This is a historic place for beer down here in Southwark – Courage used to be just along the way, Barclay Perkins too. All the hops from Kent arrived in London here, there's a lot of brewing history. I love dark beers. The fact that porters became extinct was a travesty."

Things have changed since then. Led by Meantime, the Greenwich brewery that is going from strength to strength under the leadership of Alastair Hook, London has rediscovered its drinking history. Meantime's Old Brewery at the Royal Naval College in Greenwich is intended to reconnect Londoners with their heritage, a mission O'Riordain sympathises with.

He is optimistic. "We see more and more people who are knowledgeable about beer," he says. "The most surprising thing is the general reaction – a lot of the stronger beers, on the surface you'd think they'd appeal to a certain kind of person, but when we're open on Saturday you get a varied crowd. A lot of non-beer drinkers might try one of our IPAs and they'll say, 'oh, this beer tastes like mango juice'."

It's the hops that produce the mango flavours and on the day I visited a pale ale was being made with hops from the US and New Zealand. Increasingly brewers in the UK are turning to foreign hops for stronger flavours, but very few of them use them in the volume that O'Riordain does. It's a response to the blandness of many British cask ales.

"There does seem to be a more or less prevalent attitude to cask beer in this country," he says. "There's a pub I used to go into, but I can't remember the name of anything I ever drank in there because they all taste pretty much the same. And they're created to be interchangeable, so that when one runs out you stick another one on. There's nothing really to grab your attention.

"It was when I went to the US that I realised beer can be different. If you look at the way good cheese is sold now, you know the cow's name that made the milk, what the weather is like – that's very important to us. It was only after I went to the States that I realised we could do that with beer."

O'Riordain is cagey on the future of The Kernel – as he says, changing where the beer is brewed may change how it tastes, too – but it's not hard to envisage a future in which the brewery has to move. It is at capacity now and has been for quite some time. Wherever The Kernel finds itself in the future, one thing is clear: the beer has to taste good.

"I want to keep improving," O'Riordain says. "You've got to try to improve. The thing is not to assume you've made the best beer you can, you've got to try and keep it alive, to keep it going. That's my aim."