section_path: Production/Conditioning
section_name: Conditioning
paragraph_text: Conditioning
  
  Under hygienic conditions and without other treatment, meat can be stored at above its freezing point (−1.5 °C) for about six weeks without spoilage, during which time it undergoes an aging process that increases its tenderness and flavor. During the first day after death, glycolysis continues until the accumulation of lactic acid causes the pH to reach about 5.5. The remaining glycogen, about 18 g per kg, increases the water-holding capacity and tenderness of cooked meat.
  
  Rigor mortis sets in a few hours after death as adenosine triphosphate is used up. This causes the muscle proteins actin and myosin to combine into rigid actomyosin. This in turn lowers the meat's water-holding capacity, so the meat loses water or "weeps". In muscles that enter rigor in a contracted position, actin and myosin filaments overlap and cross-bond, resulting in meat that becomes tough when cooked. Over time, muscle proteins denature in varying degree, with the exception of the collagen and elastin of connective tissue, and rigor mortis resolves. These changes mean that meat is tender and pliable when cooked just after death or after the resolution of rigor, but tough when cooked during rigor.
  
  As the muscle pigment myoglobin denatures, its iron oxidizes, which may cause a brown discoloration near the surface of the meat. Ongoing proteolysis contributes to conditioning: hypoxanthine, a breakdown product of ATP, contributes to meat's flavor and odor, as do other products of the decomposition of muscle fat and protein.