Sour beer is the hottest cold drink of 2017. The funky brew is the latest niche offering to take off in a market obsessed with finding ever more obscure and complex beers. In recent years, craft beers have soared in popularity, with particular varieties, such as extremely hoppy IPAs, gaining a strong following among a cadre of beer drinkers, who increasingly view beer with the discernment, vocabulary and sophistication once reserved for wine. Portland’s Ecliptic Brewing introduced a peach sour beer last year and saw sales of the brew double this year, spurring the brewmaster John Harris to make a new batch every week rather than every other week.