What makes a brisket different from a flank steak, like how come one kind of meat is perfectly cooked after a quick sear while the other needs hours of slow roasting to be tender? While it mostly comes down to the connective tissue called collagen, meat comes from muscle which is just strands of specialized proteins bound together by collagen. Cooking breaks collagen down into gelatin, which gives meat that melt-in-the-mouth texture. As collagen ages, those fibers get bigger and more connected, especially in the muscles that get more work. The more cross-links of collagen there are, the longer it will take for meat to get truly tender. So, a rib eye which comes from the rib area can be perfectly tender with just a light sear, but a brisket which comes from the chest area and supports a lot of the cow’s weight takes hours of cooking to tenderize.