Not long ago, quinoa was just an obscure Peruvian grain you could only buy in wholefood shops. We struggled to pronounce it (it's keen-wa, not qui-no-a), yet it was feted by food lovers as a novel addition to the familiar ranks of couscous and rice. Dieticians clucked over quinoa approvingly because it ticked the low-fat box and fitted in with government healthy eating advice to "base your meals on starchy foods". Adventurous eaters liked its slightly bitter taste and the little white curls that formed around the grains. Vegans embraced quinoa as a credibly nutritious substitute for meat. Unusual among...