Herring and their relatives may be up to 20% fat by weight, and are therefore susceptible to becoming rancid when exposed to the air. Medieval fishermen solved this problem by barreling the fish in brine, where they would keep for as much as a year. Then sometime around 1300, the Dutch and northern Germans developed a quick gutting technique that left in place a portion of the intestine rich in digestive enzymes (the pyloric caecum). During one to four months of curing in a moderate brine (16–20% salt), these enzymes circulate and supplement the activity of both muscle and skin enzymes, breaking down proteins to create a tender, luscious texture and a wonderfully complex flavor, at once fishy, meaty, and cheesy. Such herring are eaten as is, without desalting or cooking.