Why do chicken bones turn red after frozen chicken is cooked?

Cause analysis of redness of frozen chicken legs after cooking

Frozen chicken legs have more blood stasis and red and black bones (pipa legs) after being cooked. Frozen recycled raw materials will obviously show more congestion and red bone color. Because bones have the functions of hematopoiesis and blood storage, although chickens have a bleeding time of 4-5 minutes after slaughter, most of the blood in bones is still preserved. The blood vessels and muscles of the chicken leg bones are thicker, and there will be more blood left in the bones. Blood is gelatinous to some extent and can be denatured like egg white and soybean milk (coagulation and dispersion are denatured). Fresh chicken blood can be coagulated, and the coagulation effect will be more obvious after heating, but the coagulation effect will be much worse after blood freezing, especially after slow freezing.

Therefore, it can be judged that the frozen raw materials with bones, after thawing and rewarming, can't keep the gelatinous (colloidal) nature of fresh blood because the blood in bone marrow is destroyed by low temperature, which leads to infiltration into the bone and blackening the bone, while the blood flowing out of the blood vessel channel can only spread along the bone and muscle along the blood vessel, thus polluting the meat near the bone and blood vessel. If it is a fresh chicken leg, most of the blood in the bone will condense in the bone after heating. Even if some blood comes out, the coagulation effect will be better and it will not pollute the meat in a large area.