The plant-based beverage industry is a $9.8 billion market projected to grow to over $16 billion in 2018, according to Innova Market Insights, and one of its most promising entrants is oat milk. Baristas are bullish on its creamy-yet-neutral taste, its foamability and its ecological cred. Their brand of choice is Oatly, a 25-year-old food-and-beverage company founded in Malmo, Sweden, the onetime home of the author Karl Ove Knausgaard. Oatly's image has been reworked over the last five years, with graphic packaging and sleek marketing materials, including a video of the company's C.E.O. singing an ode to the oat amid a field of grains and avowals of its authenticity. "We know how it sounds," Oatly's website acknowledges. "Tall, blond, beautiful, hard to get, extremely liberal with no sense of attachment or responsibility whatsoever. Sorry to disappoint you, that's just not us."