Final Juiciness: Collagen Shrinks

As the meat’s temperature rises to 140°F/60°C, more of the proteins inside its cells coagulate and the cells become more segregated into a solid core of coagulated protein and a surrounding tube of liquid: so the meat gets progressively firmer and moister. Then between 140 and 150°F/60–65°C, the meat suddenly releases lots of juice, shrinks noticeably, and becomes chewier. These changes are caused by the denaturing of collagen in the cells’ connective-tissue sheaths, which shrink and exert new pressure on the fluid-filled cells inside them. The fluid flows copiously, the piece of meat loses a sixth or more of its volume, and its protein fibers become more densely packed and so harder to cut through. Meat served in this temperature range, the equivalent of medium-rare, is changing from juicy to dry.