Take sparkling water, some cheap alcohol usually distilled from sugar, add some fruit flavouring, stick it in a brightly coloured can — and you have a new US drinks craze, “spiked seltzer”. The undisputed leader in this market is White Claw, a brand owned by private Canadian company Mark Anthony Brands, which had an unexpected boost at the start of the summer when a mocking YouTube video by comedian Trevor Wallace went viral. Mr Wallace’s rant about the drink, which turns him into an obnoxious Hawaiian shirt-wearing frat boy as soon as he cracks open the can, spawned a meme that became so popular — “Ain’t no laws when you’re drinking Claws” — that police in several states jumped in to clarify that no such legal free pass existed.  Industry executives say spiked or “hard” seltzer taps into 20 and 30-somethings’ desires for healthier drinking options with fewer calories and carbohydrates, and little in the way of artificial ingredients and colourings. It is also further evidence of the shrinking appeal to this age group of mass-market beer, which has been losing share in the US for years.  Analysts at UBS expect spiked seltzer as a category to grow rapidly from $550m this year to...