The aging of meat is mainly the work of the muscle enzymes. Once the animal is slaughtered and the control systems in its cells stop functioning, the enzymes begin attacking other cell molecules indiscriminately, turning large flavorless molecules into smaller, flavorful fragments. They break proteins into savory amino acids; glycogen into sweet glucose; the energy currency ATP into savory IMP (inosine monophosphate); fats and fat-like membrane molecules into aromatic fatty acids. All of these breakdown products contribute to the intensely meaty, nutty flavor of aged meat. During cooking, the same products also react with each other to form new molecules that enrich the aroma further.