Every time my dad cooks steaks, he has to shoo away our outstretched forks and knives, insisting that we must let the steaks “rest” just as long as it took to cook it. It’s tough having a mouth-watering but untouchable steak staring right back at you.
Why should steaks rest after they’ve been cooked?
Surprisingly, muscle is not mostly protein. 75% of our muscles is, in fact, water! 20% is protein, and the remaining 5% are fats and carbohydrates. Muscle fibers are long and skinny cells, and each cell has many filaments made up of proteins. The “grain” of a meat refers to the direction in which the muscle fibers lie, and it is recommended that you cut your meat “against the grain.”
Heating up meat causes these proteins to denature and water to move out of the cell. That explains why burger patties always shrink on the grill; much of the water evaporates. While some water loss is inevitable, not all of it evaporates. The juices will also move towards the center of the patty or steak, where it is less hot. Therefore, after cooking, we must let our steaks rest and cool down for the juices to evenly redistribute and be reabsorbed into the cells. If we don’t let the steak sit before slicing, all the juices would flow out before they could enter the muscle cells. This rule applies not only to steaks, but many other meats like chicken, pork, and lamb.
So what is the deal with the two classifications of meat: dark and white meat? These two categories directly correspond to the type of muscle fiber.
Dark meats have slow twitch muscles.
Chicken thighs, chicken drumsticks, steak, and pork are all types of dark meats because they are made up of “slow twitch” muscle fibers. These muscles are constantly engaged by animals in order to walk or stand, so they consume a lot of energy. To support this energy need, the cells require lots of oxygen. A reddish-pink protein called myoglobin carries this oxygen for the muscles. Therefore, slow twitch muscles consume a lot of energy, require a lot of oxygen, and contain a lot of red myoglobin.
Fun fact: Myoglobin is similar to hemoglobin in that they both carry oxygen. When we exert our muscles (like when we sprint in a race), our muscles demand more oxygen. Our body responds by breathing faster and pumping oxygen-laden blood to our muscles via the hemoglobin in our blood. In oxygen-low conditions, our muscles can produce energy using an alternative method, fermentation. Unfortunately, a byproduct of this method is lactic acid, which makes our muscles feel sore.
White meats have fast twitch muscles.
White meat does not have much myoglobin because they are muscles that do not exert as much energy. For example, chickens don’t use their wings to fly, so chicken breast has less myoglobin and therefore is a white meat. Most fish are also considered white meat because they float in water and don’t have to support their bodies like land animals do (although, there may be some dark meat along the fin and tail, which are used for swimming). These less exerted muscles are called “fast twitch muscles,” or white meat.
Regardless of the type of meat, dark or white, be sure to let it rest for a few minutes before you dive in. Your patience will be rewarded with a satisfying, juicy dinner!
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