Myth: The liquid in a meat package is blood.
Fact: The liquid in a meat package is not blood, it is what meat scientists call “Purge” and it is actually a combination of water and meat proteins that drain from the meat. Myoglobin is one of those proteins, and it is the main reason the meat has a red color. Myoglobin is also what gives the “purge” liquid the red or dark pink color. Although it’s similar to the protein(hemoglobin) that gives blood it's color, it is not blood.
Liquid in a meat package should be handled carefully with proper food safety practices like the raw meat itself, because the purge can carry the same bacteria as a raw piece of meat. Wash your hands after touching meat or purge, don’t consume it unless it has been cooked to a proper temperature, and prevent cross contamination of utensils and other food.
Water is a large percentage of what makes up meat. Water is the base of the juiciness of meat which produces the texture and flavor we expect. Without the water juices the meat is dry and tough, like jerky. The proteins in meat are like a sponge. As meat ages and is handled or cut, proteins lose their ability to hold onto water. Over time, some water is released and myoglobin emanates with it, resulting in the red or pink colored liquid.
Cooking changes the purge as water evaporates from meat when it’s cooked. That’s why cooked meat is smaller than when it is raw. The myoglobin denatures and changes color during cooking. For example, rare steak may have red juices but a well done steak may have juices that are more clear. It is still important to test the internal temperature with a thermometer to assess if the meat is done cooking.