“Kölsch is sparkling, ale isn't. Apart from that, they're pretty much the same,” says Benedikt Ott, a German brewer of classic English ales and a wanderer between worlds. He is talking about the bubbles that divide us: Kölsch, a famous speciality from Ott's home town, Cologne, is the sparkling beer he grew up with. Ale is the peaceful liquid to which Ben has devoted his professional life. “Ale is still and not very refreshing but it can be rich and fruity in taste, something Kölsch is not,” he says.

Ott is wearing rubber boots. He slithers over the damp floor of Truman's Brewery in Hackney Wick. His dark hair is elegantly set in a quiff, while his grey cardigan sports the red-and-white coat of arms of his home town. Ott's English is flawless but his German isn't – every dialect-filled sentence proves him a son of Cologne. The town is one of Germany's proudest beer cities, but although Ott has learnt his craft there, he prefers working in London.

“The brewing scene here is vibrant – London is currently the beer capital of Europe. The things I can do here, I could never do in Germany,” Ott, 34, says. He has been the head brewer at Truman's for a year now. Before the engagement in Hackney Wick, he held the same position at London Fields brewery.

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Ott is not the only immigrant worker from overseas who enjoys the chances that London's booming micro-brewing industry offers. Many expatriates work in various positions at the capital's 50-plus breweries. They benefit from the freedom English beer regulations provide. It is a lot easier to open a brewery here than it is, for instance, in Germany. “When we meet with all the London brewers, I'm one of the very few at the table who has had real training. I learnt brewing in Cologne for three years and studied it later at Berlin's Technical University for two-and-a-half years,” Ott says. “Literally anybody can open a brewery here in Britain or work as a brewer.”

On the one hand, the professionalism of the German approach secures quality, he says, but it also surpresses innovation. What Ott likes most about Britain's liberal beer laws is that there is no Reinheitsgebot, as the purity law from the 1600s is called in Germany. The law only allows four ingredients to be used when brewing beer: water, malt, yeast and hops. It also dictates the order in which those ingredients are to be mixed. “Brewers in Britain are allowed to add hops to the beer at any point of the brewing process, so to change and intensify the taste of the beer. German brewers don't do that. They add hops at the beginning of the brewing and cook it with the rest of the mixture. Unfortunately, little of the hoppy taste survives the boiling.”

Some beer artisans reside next door to the Truman's brewery. Beavertown Brewery is also in Hackney Wick, an area that nowadays smells of freshly spilled beer. Beavertown is known for its wild mixtures and blends. The brewery is co-owned by Logan Plant, an Englishman, and Byron Knight, a tanned American from Los Angeles. They sit in the mezzanine of the old storehouse that is now home to Beavertown beer and tweet about their latest creations.

Downstairs, workers pile sacks of malt and hops. The bottling of the last brew has just been finished. The beer is ready to depart, the brewers relax.

Knight was attracted by the possibilities that the London beer market gives him. But in contrast to Ott, Knight grew up with independent microbreweries and lots of crafted beers around him. He never received any real brewing training. Instead, he made his own beer at home – as many Americans do in the thriving home-brewing movement.

“There was a desire for locally brewed beer in London but not many breweries were meeting the demand. We, among others, are trying to, and are doing very well so far,” Knight says. He saw a market niche in England that had long been filled in the US.

Some come for economic reasons, others for the sake of brewing freedom. But all of London's well-travelled beer immigrants contribute to the cultural exchange between British and foreign brewing styles. London's new beers are truly international. The new Fourpure Brewery, for instance, claims its beers have been inspired by the travels of its brewers: Fourpure does American-style craft beers, but combines English and American brewing techniques.

The same goes for the cosmopolitan beers of the Camden Town Brewery: the brewers there make German-style wheat beers and lagers, even a German Alt beer from a recipe their head brewer brought to England from Düsseldorf, home of the Alt beer. Camden Town Brewery also sells classic American ales.

British brewers should learn their lessons from foreign colleagues, the godfather of London craft brewing, Alastair Hook, says. Fourteen years ago, he founded Meantime, now the second-largest beer-maker in the capital, after Fuller's. Hook's impressive company is situated in Greenwich.

About 100 people work for Meantime; when I visit, many of them flit around the large stainless-steel kettles and tanks of the brewery, concerned with the precious liquids inside.

Hook's beers combine brewing traditions from all over the world: Meantime does an Indian Pale Ale, a lager, a porter, a stout, a Pilsener and even a wheat beer. The brewmaster's beers reflect his biography, as he tells me, while we are having sips of the still-fermenting lager – poured directly from the tank.

Hook studied brewing in Weihenstephan, Bavaria, where he discovered his passion for wheat beer and a love for German cleanliness and industrial perfection.

“I want all machinery, computers and programmes in this place to be technically up to date,” he says. “The standards in here are no different from those in big German breweries. Keeping this up is expensive but it all pays out in the end – the quality of our beer is just so good.”

He regularly travels to find the best ingredients for his beer but he also likes to learn from other countries. His years in Germany have not only been a professional success but also a personal one: Hook's wife is German and he peppers his sentences with technical German brewing terms.

“When I see those young brewers from all over the world coming to London in order to seek their fortunes here, I think that our English brewers should do the same thing: go abroad for a while, leave the island, study the different traditions, pick up new ideas and come back with enough experience to start a business,” he says.

The future of London's beers, it seems, might be bubbling and cold, as the influence from overseas grows. Many microbreweries are already using ingredients from all over the world to brew their beers.

“Why should London brewers not produce Czech-style Pilseners and German lagers?” asks Hook, whose company already does a variant of both.

He is right: why bring in poor imported lager when we can produce our own good ones? No doubt the capital's brewers will drink to that.