The appearance of meat changes in two different ways during cooking. Initially it’s somewhat translucent because its cells are filled with a relatively loose meshwork of proteins suspended in water. When heated to about 120°F/50°C, it develops a white opacity as heat-sensitive myosin denatures and coagulates into clumps large enough to scatter light. This change causes red meat color to lighten from red to pink, long before the red pigments themselves are affected. Then, around 140°F/60°C, red myoglobin begins to denature into a tan-colored version called hemichrome. As this change proceeds, meat color shifts from pink to brown-gray.