Gelatin

The strength of the collagen that forms connective tissue depends on the degree to which its protein molecules are chemically connected, a process known as cross-linking of tropocollagen molecules. When an animal exercises its muscles, the collagen becomes stronger, making the muscles tougher with age. Similarly, those muscles that are required to perform heavy work are also tougher. Newborn animals contain loosely bound collagen, which easily breaks down into gelatin. Meat from younger animals is more tender, not because it has a lower collagen content, but because the collagen has fewer cross-linkages.