Malt vinegar is a dark brown, robustly sour condiment made by fermenting malted barley twice over: the grain's starches are converted to sugars and brewed into an unhopped ale, which acetic-acid bacteria then sour into vinegar. Deeper, maltier and more toasty than wine or distilled vinegars, it is inseparable from British fish and chips, and it is the backbone of pickled onions, ploughman's chutneys and the classic brown table sauces of the British Isles.