I was on a search for a scientific reason as to why grass-fed beef is dark, dark red or in our case almost a dark purple. I found that the science behind why meats are darker/lighter in color is pretty interesting but not easy to understand or explain. I need to get the book The Science of Cooking to get the even more detailed explanation.
So here goes nothing on the simple answer. A muscle needs oxygen. Typically a muscle can get oxygen from the blood flowing through the muscle. However, muscles that are heavily used may not get enough oxygen from the blood inside the muscles so they resort to oxygen stored in myoglobin (a protein molecule). When myoglobin is carrying oxygen, it is red. So because grass fed animals have to walk around the pasture to find their food and walk around to get their water, run with the calves, etc. their muscles need more of the oxygen stored in myoglobin as they won't get enough from the blood in the muscle, and will be darker as a result.
Now I would assume that if you had a grain fed animal that had to walk from one end of the pasture to get their food and another end to get their water, then maybe those animals would have darker meet as well. So the color has nothing to do with food (grain/grass) but all to do with exercise.
This is also why turkey and chicken legs are dark meat while the breasts are white meat. The legs are working so they have more myoglobin. Same goes with different cuts of pork. If the muscle is getting used-- it's darker.
Now darker meat has more flavor but the danger is that it can be tough so must be cooked properly.
We've been plowing steadily through our beef and I can say it's all dark, dark red and so, so, so flavorful.
So there you go--- lesson of the day!!
