Image caption The Molson Coors brewing complex, formerly the home of the famous Bass brewery, still dominates the centre of the town

From Beijing to San Francisco, brewers are trying to recreate the unique chemical conditions produced naturally beneath a small Midlands town. But what is the secret of the Burton snatch?

In downtown Beijing, parched commuters have traditionally slaked their thirsts with fruit juice or tea but many are following the global craft beer boom and turning to refreshing pale ales.

Beer is booming, and after President Xi Jinping's visit to the UK last year China is gaining a taste for British beer.

What they probably do not realise is they have a small town in the English Midlands to thank for it.

For many people, British beer means Burton-upon-Trent. And the reason for this is found in the rocks beneath the Staffordshire town.

Image copyright PA Image caption Chinese President Xi Jinping visited a pub with Prime Minister David Cameron on a state visit to the UK last year, leading to a boom in imports of British beer in his home country

Burton beer is known for its earthy, eggy smell - known in brewing circles as "Burton snatch" - a sure sign of the ale's quality and provenance.

This is created by the water trickling through unusually thick bands of gypsum before resting in underground aquifers.

This quality has long been imitated by rival brewers elsewhere in the UK and the technique is now being employed around the world.

Will Yorke, who runs Beijing-based Arrow Factory Brewing, has been in China's capital since 1997, when he remembers major international beers such as Guinness were seen as "a special treat" due to their limited availability.

"Having grown up in the UK, I was influenced by British beers, and while many craft brewers enjoy making USA-style craft beer, I was keen to also try to represent the long history and rich culture of British brewing and beers," he said.

"Burton beers are some of the more outstanding, and its source of water famous for its effect on the beer."

Brewing in Burton

Image caption This example of the Burton Union System, a fermentation system once used by many of the town's brewers, stands in the grounds of the National Brewery Centre. It is one of many distinctive buildings in the town centre harking back to its brewing heyday

The industry took off in the early stages of the Industrial Revolution, with brewers such as William Bass and Samuel Allsopp laying the foundations for success.

Once the railway reached Burton the town's beers made it to London and on to India, where the clarity, quality and reliability of Burton beers was highly regarded.

At one point Burton produced about a quarter of the UK's beer and more than 30 breweries once operated there.

Influential brewers served as aldermen, councillors and MPs. A group of ennobled brewers became known as "the Beerage".

Brewing in Burton declined as major breweries merged or were taken over from the mid-20th Century.

But what is so good about the beer? The Honourable Order of Bass Drinkers makes annual trips to the birthplace of the famous tipple, whose famous red triangle is the oldest registered trademark in the UK.

Its secretary, Stanley Goldsmith, says the Burton snatch is still a unique treat.

Image caption Though the town is still held in high regard by brewers across the world, signs of decline around Burton town centre are noticeable

"Part of the enjoyment is is smelling the beer without drinking it," he says.

"If it's in a really good condition and has a good, small head on it I like to have a good smell for a couple of minutes first - it increases the anticipation of what's to come."

Perfect brewing in Beijing, a city with huge problems with water shortages and pollution, is not straightforward but Mr Yorke is now successfully adding gypsum and salts such as magnesium sulphate to the local water to replicate the famous eggy smell.

A similar process is also happening in the United States, where Burton's reputation is strong.

The town even inspired an unusual pilgrimage from sunny southern California.

Beer-lover Mitch Steele, brewmaster with Stone Brewing Company, was visiting England to take part in a beer festival, and when asked where he wanted to go during a few days of downtime, he had no doubts about heading from London to the Midlands.

"I said I wanted to go to Burton, because it means so much to brewers," he said.

"The guys we were with were really surprised, they did not expect us to say that."

Mitch is such a fan of the town's legacy he once named a beer in honour of the Burton snatch.

Image copyright Stone Brewing Image caption Mitch Steele doing his day job as brewmaster for Stone Brewing, near San Diego in California. He first learned about Burton-upon-Trent's brewing history from home-brewers in the US before making what he called a "pilgrimage" to the town

He thinks Burton's illustrious history and impact on worldwide brewing should see it ranked among the powerhouses of the industry.

"It's as important to the beer world as Munich, the Czech Republic or Belgium. It's a brewery centre, and I find it very inspiring."

American enthusiasm came as a surprise for Richard Catlin, who founded Burton Town Brewery in an industrial unit in his hometown in February.

"I didn't realise the reputation it had until I was in a bar in America and I told this guy I was from Burton," he said.

"Everyone went quiet, and they treated me like I was some sort of beer god. They kept buying me beers and asking me to try things - they thought I knew everything about it.

"I suppose it gave me a bit of an awakening about what Burton means to the beer world."