• Tuesday, November 25, 2014

    Packaging questions: Purge

    It’s one of my most commonly-asked questions.

    What is the deal with that blood or water in my package of meat?
    Beef steaks and purge
    Photo courtesy Macc Rigdon

    When you take your tasty cut of meat out of the package, there is a pinkish liquid that is left behind. Most of the time, there is even a little soaker pad in the package to soak it up.

    What is that stuff?

    Short answer:

    It’s a combination of water, lactic acid, and meat pigments that seeped out of the meat.

    Longer answer:

    Soaker pad in a chicken tray
    In science class, we all learned that our bodies are largely made up of water. The same is true for animals, and a high percentage of that water is held in the muscles and stays in the muscle when it’s converted to meat.

    Water in the meat is what creates the juiciness we experience when we eat a juicy steak, a tender ham, or a succulent turkey (#tokenthanksgivingreference). Water helps give meat the texture and flavor we expect. Meat without water is jerky, dry and tough.

    Think of the proteins in meat as a sponge. As the meat ages and the more it is handled (cut, shipped, packaged, etc.), the protein sponge loses its ability to hold onto water. So, the water seeps out of the meat over time.

    When the water seeps out, the protein that gives meat its color (myoglobin) flows out with the water. That protein gives the purge its color. Although it’s similar to the protein that gives blood its color (hemoglobin), it is not blood.

    Pork chops in a purge loss study
    Meat scientists have lots of
    creative ways to measure purge
    Photo courtesy Macc Rigdon
    The ability of the meat to hang on the water is dependent on several different things, including the species and age of the animal, the fatness and grade of the meat, the length of time since the animal was harvested, which muscle the cut of meat was from, and how the meat has been handled and processed. Meat scientists spend hours and hours trying to figure out purge and what causes it.

    Sometimes meat processors will add a solution to meat cuts to make them more tender, flavorful and juicy. That solution can change the amount of purge in a package, but the presence of purge does not automatically mean that water or anything has been added to the meat. Most of the time, purge is just a natural result of water leaving the muscle.

    Some of the water in meat will evaporate out when it’s cooked. That’s why cooked meat is lighter in weight than raw. As the meat is cooked, the myoglobin will denature and lose its red color. So the juice that runs out of a rare steak may still be pink or red, but the juice from a cooked steak is colorless.

    So, the water in meat packages is just purge, water and a little myoglobin. Maybe we should give it a better name.
    Vacuum packaged pork with purge
    Photo courtesy Macc Rigdon 


    Something I learned from writing this blog: When you ask your meat-scientist friends to send you pictures of purge, be prepared to get a whole lot of them! I wasn’t pleased with my own photos, and a whole community of meat scientists responded when I sent out a request for pictures on facebook. Thanks, friends!