Basic Meat Science For Cooks
"My foe, my enemy, is an animal. In order to conquer him I have to think like an animal and, whenever possible, to look like one. I've got to get inside this dude's pelt." Carl Spakler (Bill Murray) in Caddyshack, 1980
As meat is heated, it undergoes physical and chemical changes called denaturing, and as scientific as this process is, it is also magic. It is a complex process, but a basic understanding is the first step in making an omnivore's delight.
What is meat?
Meat is cut from the muscles of mammals and birds. For some reason, fish muscle is not considered meat by some people, but it should be.
Lean muscle tissue typically breaks down like this: Water (about 75%), protein (20%), fats (5%), carbohydrates (1%), and vitamins, sugars, and minerals (1%).
Different cuts can differ significantly. Shoulder meat tends to have a lot more fat and connective tissue. Pork rib meat, for example, is more like 65% water, 18% protein, 15% fat, and 2% vitamins, sugars, and minerals.
With that much water in the meat, any loss you might have from stabbing it with a thermometer or an occasional stab with a fork is minor, so don't let the snobs tell you that you are going to ruin the meat if you use a thermometer.
Muscle cells. Muscle cells are more frequently called muscle fibers because they are shaped like tubes. Fibers bundled together are called sheaths, and sheaths bundled together are called muscle or meat.
The fibers, about the thickness of a human hair, are filled with water and several types of protein, among them myosin and actin which bind water and act like motors by contracting and relaxing on command. Myoglobin is another important protein in muscle fibers. Myoglobin receives oxygen and iron from hemoglobin in blood, fuel necessary for muscles to function. Myosin and actin are not water soluble, but myoglobin is and myoglobin dissolved in water is the pink liquid we see seeping out from a package of raw meat or spilling onto the plate when we cut into cooked meat. It also contains other proteins, enzymes. It is not blood.
As an animal ages, grows, and exercises, muscle fibers get thicker and tougher. So do the connective tissues.
Connective tissue. Connective tissue is most obvious in the form of tendons that connect muscles to bones. It is also visible as the thin shiny sheathing that wraps around muscles called silverskin and in ligaments that connect muscles to other muscles. These tougher, chewier, rebber band-like connective tissues are mostly protein appropriately named elastin. We call them gristle and they shrink when heated and become unchewable. As with muscle fibers, connective tissues thicken and get tougher as the animal ages.
A softer connective tissue called collagen is scattered throughout the muscle, often surrounding fibers and sheaths holding them together. When you cook, collagen melts and turns to a rich liquid called gelatin, the same stuff Jell-O is made from. Muscle fibers, no longer bound together by collagen, are now uniformly coated with a soft, gelatinous lubricant. This gives meat a wonderful silky texture and adds moisture. And yes, this is pretty much the same thing the Hollywood wives have injected in their faces to get rid of wrinkles.
Lean meats like beef or pork loin and tenderloin, as well as most chicken and turkey, don't have much collagen. When cooking tough cuts of meat with lots of connective tissue, like ribs, brisket, and shoulder, it is important to liquefy connective tissue into gelatin. This takes time. That's why these cuts are often cooked low and slow. Muscle fibers start seizing up around 125°F to 140°F if heated quickly. But when heated slowly, the rubber band-like connective tissues have time to relax and do not squeeze tightly. The AmazingRibs.com science advisor Prof. Greg Blonder says "Think of silly putty. Pressed hard and quickly, it acts like a rigid solid. Pressed slowly, it flows." When heated slowly, the muscle fibers, instead of wringing out moisture, relax and simply let water linger inside until evaporation drives it out.
After it melts, as it chills, gelatin can solidify into that jiggly stuff which, with a little processing, can then be called aspic and served at bridge clubs. Here's a pot of the stuff made simply by boiling a couple of chicken carcasses after I ate the meat meat and then chilled. The white is fat, most of which I have removed, and the tan is gelatin.
Fat. Fats (lipids) and oxygen are the main fuels that powers muscles. It is packed with calories, or potential energy released when the chemical bonds are broken. From a culinary standpoint, fat comes in three types:
1) Subcutaneous fats are the thick hard layers beneath the skin.
2) Intermuscular fats are layers between muscle groups.
3) Intramuscular fats woven amongst the muscle fibers and sheaths add moisture, texture, and flavor to cooked meat. These threads of intramuscular fat are called marbling because they have a striated look similar to marble.
Large fat deposits can also be found around organs, especially kidneys. On hogs, the best fat from a culinary standpoint, especially if you make pie crusts, is called leaf lard, and it comes from around the kidneys.
Fat is crucial to meat texture. Waxy when it is cold, at about 130°F to 140°F fat starts to melt and lubricate the muscle fibers just as they are getting tougher and drier under the heat. Fat does not evaporate as does water when you are cooking.
Fat is also the source of much of the flavor in meat. It absorbs and stores many of the aromatic compounds in the animal's food. As the animal ages the flavor compounds build up and get stronger. After the animal is slaughtered, the fat can turn rancid if stored too warm, too long, or in contact with oxygen. So we have a tradeoff. The muscle fibers and connective tissues get tougher as the animal ages and exercises, while the fat accumulates and builds flavor.
Fats, especially animal fats are the subject of a great deal of debate among scientists, doctors, dietitians, and health faddists. For many years they were thought to be dangerous and to be avoided. It is now thought that fats, even animal fats, contain many beneficial properties, and some argue that, in moderation, they are essential for health. A great deal of interesting research on the subject is going on as I type this. A great deal of research is contradictory. I am not a doctor, but I read a lot about food and diet, even technical research. My conclusion: No food is dangerous in moderation. No food is magically healthy. Read more about what I have learned about food and health in this article.
Fluids. Most of the liquid in meat is water. The reddish color in meat and its juices is not caused by blood. It is the protein myoglobin dissolved in water. Myoglobin is found only in muscle, not in the blood stream. The blood was pretty much all drained out in the slaughter house. If the stuff on your plate when you sliced a steak was blood, it would be much darker, like human blood, and it would coagulate, like human blood. If the fluids were blood, then pork and chicken would be dark red. It's mostly just water, so let's stop grossing out our kids, and just call it juice. OK?
When animals are alive, the pH of the muscle fibers is about 6.8 on a scale of 14. The lower the number, the higher the acidity, the higher the number the more alkalinity. At 6.8 living muscle is just about neutral. When the animal dies, the pH declines to about 5.5, making it acidic. At this pH muscle fibers form bunches squeezing out juice, called purge.
Slow twitch vs. fast twitch muscles
Muscle fibers need fat and oxygen for fuel. Fat comes from fatty acids in the animal's blood that were created by digestion of its food. Oxygen is carried by the protein hemoglobin in the blood stream and it hands the oxygen to myoglobin, within the muscles.
In general, the more exercise a muscle gets, the tougher it is, and the more oxygen laden myoglobin it needs. Myoglobin turns meat darker and makes it more flavorful. Dark meats, like chicken thighs are made of "slow twitch" muscles designed for slow steady movement and endurance, and are loaded with juicy myoglobin. White meats, like chicken breasts, are mostly "fast twitch" muscles, designed for brief bursts of energy, and have less myoglobin. Dark meats also have more fat for energy.
When cooked, slow twitch muscles have more moisture and fat and are more flavorful than white meat. White meats contains less moisture and fat, and so it dries out more easily when cooking. The legs and thighs of chickens and turkeys get more exercise standing and walking, so they have lots of slow-twitch muscles, more pigment, more juice, more fat, and more flavor. They are also slightly more forgiving when being cooked. Modern chickens and turkeys have been bred for large breasts because white meat is more popular in this country (and I for one, can't understand why).
Ducks and geese are designed for flying and swimming and they get more exercise than chickens and turkeys, so they have more dark meat. Duck breasts are deep purple, almost the same color as lamb or beef.
Modern domestic pigs have been bred to have less intra-muscular fat for a health fad conscious society, and they don't get much exercise, so they have become "the other white meat".
Beef is all pretty much the same color, but slow twitch muscles like flank steak have bigger richer flavor.
Fish live in a practically weightless environment, so their muscles are very different, with very little connective tissue. That's one of the reasons why fish never gets tough. But it can dry out because there is not much collagen to moisturize the fibers. The color and texture of fish varies depending on the life it leads. Small fish swim with quick darting motions have mostly fast-twitch muscles and white meat, and flounder, which lives on the bottom, has delicate flaky flesh. Torpedos like tuna and swordfish swim long distances with slow steady tail movements so they have have firmer, darker, sometimes even red flesh. For these reasons, and others, fish can spoil within days of being caught while red meats keep much longer.
Proper cooking and serving temp
Because different cuts of meat vary significantly in tenderness, fat content, and collagen content, some must be cooked hot and fast to be at their best, some must be cooked low and slow, and some must be cooked with a combination on both to reach their optimum. Click here to read an article on the subject of cooking temps.
You cannot tell if meat is safe or cooked to the proper temp by looking at it. Sometimes vegetables in the grill can produce gases that alter meat color. When you cut into meat to look at it, it can change in a few minutes after it has been exposed to oxygen. Compounds in marinades and brines can impact color. There is only one way to tell if meat is at its optimum quality and safty: With a thermometer, preferably a digital.
The higher the internal temp the meat achieves, the more water it squeezes out and the drier it gets. In general, most meats are juiciest and most tender when cooked to medium rare, 130 to 135°F internal temperature.
But that's not hot enough for safety in some meats. Ground meats and poultry are health risks at those temps. Ground meats need to be cooked to 160°F, and poultry needs to go to 165°F to kill the pathogenic bacteria. But there's more to the story than that. You can actually serve these at lower temps if you know the rules. Read my article on meat temperatures.
Meats with a lot of connective tissue such as beef and pork ribs, pork shoulder, or beef brisket, are too tough at these lower temps. They need to go up to 190 to 205°F in order to gelatinize collagens and melt fats. That's well past well done, and yes, water is lost, but the melted gelatin and fats lube the meat and make it tender and juicy.
Be aware that if you let meat sit around after you remove it from the heat, the heat built up in the outer layers will push down to the center and overcook the meat, a process called carryover. The good news is that resting meat is an old husband's tale and it does little to improve juiciness. For more about ideal serving temps, read my detailed Food Temperature Guide with handy printout for your fridge.
Brown is beautiful, black is bad
As meat cooks, the most magical transformation is the Maillard reaction. It is named for a French scientist who discovered the phenomenon in the early 1900s. The surface turns brown and crunchy and gets ambrosial. Who doesn't love the crusty exterior of a slice of roast beef or the crust on a roasted marshmallow? We don't think twice about it, but that brown on the surface of a steak is hundreds of compounds that are created when heat, especially heat above 300°F, starts changing the shape and chemical structure of the amino acids and sugars on the surface of the meat. Click here to learn more about the Maillard reaction.
What you don't want is black meat. Let it go too far and it turns to carbon. Carbonized meat may be unhealthy.
Pretty in pink
Many smoked meats develop a smoke ring, a bright pink color just under the surface. Some people think the pink color means the meat is raw, but nothing could be further from the truth. It is a common phenomenon called the smoke ring. Some people think the smoke ring improves taste. That's a myth too. Click here to read more about the smoke ring and what causes it.
What causes properly cooked pork and poultry to be pink, even if it is not smoked?
Several factors: Gases in the atmosphere of an oven, particularly carbon monoxide, can react with myooglobin in meat and turn it pink, especially on the outer edges. They occur in all ovens, especially those that heat by combustion such as gas, charcoal, or wood. They even are present in electric ovens, but to a much lesser degree. When grilling or smoking, there are more of these gases. They more easily penetrate the thinner skin and fat layers of younger animals, so age of the animal is also a factor.
Also, meats with high levels of naturally occurring compounds such as myoglobin are more likely to turn pink. Nitrites in meat can also cause pinking. Nitrites are converted from nitrates in feed and water by microorganisms that are in the animal. Nitrates naturally occur in many leafy vegetables, and can transfer to the meat during cooking, from a rub or braise.
In fact, grocery store meat trays are occasionally packed with carbon monoxide or nitrogen to keep the meat in the pink.
The best way to test for doneness of any meat is to use a food thermometer. Color is not a reliable guide. A classic example is chicken. It has long been thought that when chicken juices run clear the meat is safe, but modern chicken farming has changed that. Click here to read how we bust the myth of clear chicken juices. Click here for a buying guide to food thermometers.
Why is red meat sometimes bright red on the outside and dull gray on the inside?
Fresh cut or ground beef is purplish-red in color. Oxygen reacts with the pigments in red meat to form the bright red color in the grocery store. The interior of the meat may be gray or brown because oxygen has not penetrated into the muscle. This is normal. If, however, all the meat in the package has turned gray or brown, it may be spoiling.
Meat in my fridge is turning brown
At first oxygen reacts with pigments to turn it red. After a while the meat starts to oxidize, and it turns brown, the same way an apple or potato turn brown.
Why does my meat shine like a rainbow?
It is simply a fluke of the right lighting striking the surface if the surface has been cut a certain way. Strictly refraction, not bacteria or an oil slick.
Why is my meat green?
Bad bacteria. Throw it out.
There are dry white spots on my meat from the freezer
That's freezer burn. It's like frostbite. The meat has probably been in the freezer too long and/or it was not wrapped tight. It is still safe, but the burned parts will probably be dry and bland. Trim it off and cook it, but don't serve it to Mom or the boss.
My meat smells funny, what should I do?
Sometimes meat will smell a bit odd when you take it out of a vacuum sealed plastic bag, but the smell should dissdipate quickly, within five minutes. If it still smells funny, then chances are it is funny. Throw it out.