Rohit Dugar is standing in front of a fermentation tank at his Ap Lei Chau brewery, Young Master Ales, when he opens a valve and fills a small glass with amber liquid. He takes a sip. "I think it needs more salt." That's not something you expect to hear about a beer, but Dugar is not making an ordinary brew. His Cha Chaan Teng Gose is based on a centuries-old German style of beer whose tart and slightly salty flavours bear some resemblance to lemonade. Young Master's version includes salted lime, a nod to the classic haam ling chut (salted lime with 7 Up), a staple of Hong Kong-style cafes. Dugar and his master brewer, Ulrich Altbauer, first made the the gose as a one-off experiment earlier this year. But it proved so popular over the summer that they recently brewed a second batch for autumn. It will be one of the 551 beers available at this year's Beertopia craft beer festival, on October 9 and 10 at the Central harbourfront. Done well, it's one of the most intriguing flavours out there; done poorly, it will make you want to throw out the entire beer Jeff Boda, Hop Leaf The gose won't be alone in the festival's sour beer category. Although they represent just a fraction of the overall craft beer market, sours are a growing niche, beloved by beer geeks for their complex and surprising range of flavours that are not usually associated with the brew. "There are hundreds of different of flavours in beers, but sour is one people normally don't get to until later on," says Jeff Boda, founder of craft beer importer Hop Leaf. "Done well, it's one of the most intriguing flavours out there; done poorly, it will make you want to throw out the entire beer." Sour beers encompass a huge range of styles that have roots in Belgium and Germany, from the dry, farmyard profile of lambics to the light-bodied tartness of a Berliner Weisse. Their origins go back hundreds of years to the days when most beers were sour - more by accident than anything else. In recent years, though, avant-garde craft brewers have experimented with old styles and invented new ones, such as Young Master's limited release Tai Sui, which is a dark rye ale fermented with locally cultured sourdough yeast and aged in rye whiskey barrels. There are a number of different ways to make beer sour. One of the most popular is by adding Lactobacillus bacteria - the same thing that turns milk into yogurt - during an early stage of brewing. Another is to introduce strains of wild yeast from the Brettanomyces family, which imparts an earthy flavour often described as "farmyard", "horse blanket" or "funk". Belgian lambics are fermented in open vats that are exposed to whatever ambient yeast is floating around, a process that flies in the face of most brewing traditions, which insist on rigorously sanitised equipment. The result is certainly an acquired taste, but one that many beer drinkers have picked up rather quickly, if the surging popularity of sour beers in North America is any indication. "It seems like every brewery is doing a sour these days," says Rick Green, a former Hong Kong resident who is now involved in the Vancouver craft beer scene. "People are rediscovering the full spectrum of their tastebuds." Here in Hong Kong, Young Master is so far the only brewery to have dabbled in sour beers, but international sours are readily available thanks to the city's craft importers. "Sour beers are definitely gaining momentum and popularity in Hong Kong," says Laurie Goldberg, founder of AmeriCraft Imports, which imports a number of sour and wild-fermented beers from Jolly Pumpkin Artisan Ales in Michigan, three of which won prizes at this year's Hong Kong International Beer Awards. Goldberg didn't like sour beers at first because she thought they didn't taste like regular beer. She now counts them among her favourites. "Once I opened my mind and focused on the taste alone, and stopped thinking about what I thought beer should taste like, I really enjoyed the flavours," she says. Hong Kong drinkers seem to agree. Dugar says the response to the Cha Chaan Teng Gose was more enthusiastic than expected, especially among local Chinese drinkers at TAP, a Young Master-affiliated bar in Mong Kok. Boda says Anderson Valley's Blood Orange Gose, imported by Hop Leaf from California, was another surprise hit. "When we've had a sour on tap it's always gone down quite well," says Toby Cooper, owner of The Globe pub in Central. "Sour beers are quite an easy sell in Asia as everyone is familiar with the flavour profile from Asian cooking." Another factor that may help win Hong Kong drinkers over to sours is the enduring popularity of wine. "For people who don't like beer, but they like wine, that range of sour styles are more vinous in character," says Green. Beertopia founder Jonathan So agrees. "Drinkers who enjoy white wine might find similarities between the two." There are as many types of sours as there are ingredients that you can add, and different barrels you can put them into - so the possibilities are endless Danny Wong, The Bottle Shop Beer geeks don't need much convincing. Boda is partial to goses, which he thinks are more refreshing than light lagers. "To me it's the perfect beer for a day when it's 33 degrees Celsius and humid outside," he says. The Bottle Shop's founder Danny Wong recommends Luksus One, a hard-to-categorise sour beer made with beetroot by Evil Twin Brewing in New York. "The flavour is just light, refreshing, slightly sour, with lots of beetroot flavours. It's just an awesome beer that goes with many types of food." Wong is looking forward to more sour beers in Hong Kong - if only for the benefit of his own tastebuds. "To imagine there's something even more refreshing than the traditional light beers, but with lots of complexity and character, that's what makes sours so amazing," he says. "There are as many types of sours as there are ingredients that you can add, and different barrels you can put them into - so the possibilities are endless." 10 sour beers to try at Beertopia Cha Chaan Teng Gose (Young Master Ales) Light, citrusy and moderately tart with just a hint of saltiness. Tai Sui (Young Master Ales) Rich and complex, with a faint sourness that balances rye spiciness and buttery oak. Evil Twin's Luksus One (The Bottle Shop) Quaffable yet surprising, with notes of cinnamon and beetroot. 8Wired Wild Feijoa Sour Ale 2013 (The Bottle Shop) Barrel-aged with New Zealand's beguiling feijoa fruit. Anderson Valley Blood Orange Gose (Hop Leaf) Thirst-quenching with a juicy blood orange flavour. Mikkeller Blå Spøgelse (Hop Leaf) Sour blueberry lambic with a crisp, dry tartness and earthy berry notes. Mikkeller Mastodon Mother Puncher Farmhouse IPA (Hop Leaf) Hoppy, fruity and funky, with a pronounced sourness from the addition of passionfruit. Jolly Pumpkin Oro de Calabaza (Americraft) Dry, spicy and citrusy with a slight tart note at the end of each taste. Rodenbach (Faith International) A robust vinous sourness, like an aged Chinese vinegar. Petrus Aged Pale (Belicious) Lemony and assertively tart with hints of oak.