What is meat?

Every time you step up to your grill or into your kitchen, you begin a science experiment. As meat is heated, it undergoes physical and chemical changes, and as scientific as these processes are, they are also magical. A basic understanding can help you cook juicier chicken breasts and more tender steaks. This article is an overview and the links within take you to articles that explain the concepts in greater detail.

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.

On average, lean muscle tissue typically breaks down like this: Water (about 75%), protein (18%), fats (5%), carbohydrates, salt, vitamins, sugars, and minerals (2%). Here are some specifics.

Different cuts from within an animal can differ significantly. As shown above, the average water content of pork is 69%. Pork rib meat, however, is more like 65% water, 18% protein, 15% fat, and 2% carbohydrates, salt, vitamins, sugars, and minerals. Even so, 65% is a pretty high percentage of water. 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 to check its temp or a fork to turn it. To illustrate: if you have an 8-ounce filet mignon, 6 ounces is water. Stab it and a few drops leak out from the puncture site, an insignificant part of the 6 ounces. Meat is not a balloon that goes phffffft and deflates when you poke it with a thermometer or fork

Muscle cells

Muscle cells are more frequently called muscle fibers because they are shaped like tubes. Muscle fibers bundled together are called sheaths, and sheaths bundled together are called muscle or meat.

The fibers, about the thickness of a human hair, contain several types of protein, among them myosin and actin which bind up water and act like living motors by contracting and relaxing on command. As animal ages, grows, and exercises, its muscle fibers get thicker and tougher. And muscles like shoulders and legs get thicker and tougher than the smaller, more tender muscles call "tenderloins" that run along the animal's spine.

Myoglobin is another important protein in muscle fibers. Myoglobin receives oxygen and iron from hemoglobin in the blood, the fuel necessary for muscles to function. Myosin and actin are not water-soluble, but myoglobin is water-soluble, 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. When warmed, those meat juices lose their red color, become pink, and eventually tan or gray. Fibers also contain other proteins: enzymes. Enzymes play an important role in aging meat.

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, rubber band-like connective tissues are mostly protein and appropriately named elastin. We call them gristle and they shrink when heated and become unchewable. As with muscle fibers, connective tissues thicken and toughen as an animal exercises and 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, similar to the stuff Jell-O is made from. Cooked muscle fibers, no longer bound together by collagen, are now uniformly coated with a soft, gelatinous lubricant. This smooth and sensual substance enrobes meat in a wonderfully silken texture and adds moisture. And yes, this is pretty much the same stuff the Hollywood wives have injected into 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 the meat's connective tissue into gelatin: that's what makes these tough meats taste tender. 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. In general, it is best to cook all meats at about 225°F. Slow roasting does wonders for meat. 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 filtering, 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 in water after I ate the meat, discarded the bones, and chilled the liquid. The white is fat, most of which I have removed, and the tan is jiggly gelatin.

Fats

Fats (lipids) and oxygen are the main fuels that power muscles. Fats are packed with calories, which are potential energy released when the chemical bonds are broken. From a culinary standpoint, fat comes in three types (see the photo at the top of the page):

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 improve meat's moisture, texture, and flavor when cooked. 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 of this type, at least from a culinary standpoint, especially if you make pie crusts, is called leaf lard, and it comes from around the kidneys.

Fats are crucial to meat texture. Waxy when cold, fats start to melt around 130°F to 140°F, lubricating muscle fibers just as they are getting tougher and drier from the heat. Fat does not evaporate like water when you are cooking.

Fat also provides much of the flavor in the meat. It absorbs and stores many of the aromatic compounds in the animal's food. As the animal ages, those flavor compounds build up and get more noticeable. 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 great debate among scientists, doctors, dietitians, and health faddists. For many years, animal fats were thought to be dangerous and avoided. It is now thought that fats, even animal fats, contain many beneficial components, and current science argues 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. 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 bloodstream. The blood is pretty much all drained out in the slaughterhouse. If the stuff on your plate when you sliced 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? Every time you call meat juices blood, a bell rings and a teenager becomes a vegan. Click here to Tweet this bit of wisdom

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 and less acidic. 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 and squeeze out the juice, called a purge, and that is the juice you see in packages of meat that is absorbed by the diapers they put under the meat.

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 the digestion of its food. Oxygen is carried by the protein hemoglobin in the bloodstream, 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 that have evolved to endure slow, steady movement, and they are loaded with juicy myoglobin. White meats, like chicken breasts, are mostly "fast-twitch" muscles, which are better suited to brief bursts of energy, and they have less myoglobin. Dark meats also have more fat for energy.

When cooked, the slow-twitch muscles in dark meat have more moisture and fat and are more flavorful than white meat. White meats contain less moisture and fat, and they dry out more easily when cooked. The legs and thighs of chickens and turkeys are good examples. These animals get more exercise standing and walking than flying, so the legs and thighs have lots of slow-twitch muscles, more pigment, more juice, more fat, and more flavor. They are also slightly more forgiving when 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). I'll take tough and flavorful over tender and mild any day.

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Ducks and geese excel at flying and swimming, and they get more exercise than chickens and turkeys, so these birds have more dark meat. Duck breasts are deep purple, almost the same color as lamb or beef.

When the conventional wisdom was that dietary fat could cause heart and arterial problems, domestic pigs were bred to have less intramuscular fat. The modern pig does not get much exercise due to its transmogrification into "the other white meat." In recent years, research has questioned the relationship between dietary fat and health, and many experts extol fat's benefits.

Beef is all pretty much the same color, but slow-twitch muscles like flank steak have bigger, richer flavor than some of the lesser-used muscles like tenderloin.

Fish live in a practically weightless environment, so their muscles are very different. Fish muscles have very little connective tissue, and that's one reason why fish never gets as tough as pork when cooked. But fish can dry out because there is not much collagen to moisturize the muscle fibers. The color and texture of fish vary depending on the life it leads. Small fish that swim with quick darting motions have mostly fast-twitch muscles and white meat, while flounder, which lives on the seafloor, has delicate flaky flesh. Torpedos like tuna and swordfish swim long distances with slow steady tail movements, so they have had 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.

Brown is beautiful, black is bad

As meat cooks, the most magical transformation that occurs 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 in the aroma. Who doesn't love the crispy exterior of a slice of roast beef, the browned crust on freshly baked bread, or the crackling surface of a roasted marshmallow? We don't think twice about it, but that brown color on the surface is the mark of hundreds of compounds created when heat, especially heat above 300°F, starts changing the shape and chemical structure of the amino acids, carbohydrates, and sugars on the surface of the meat. Click here to learn more about the Maillard reaction and caramelization.

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

There's another color you may notice in cooked meat: pink. Many smoked types of meat turn bright pink just under the surface. Some people think that the pink color means that meat is raw, but not in this case. If the meat were undercooked, the pink would be in the center, not just below the surface. Pink meat near the surface is a common phenomenon called the smoke ring and it is caused by gases in smoke preserving the color of myoglobin. 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 myoglobin in meat and turn it pink, especially on the outer edges. These gases occur in all ovens, especially those that heat by combustion such as gas, charcoal, or wood. They are also 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 the 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 within the animal. Nitrates naturally occur in many leafy vegetables and can transfer to the meat during cooking, say, 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.

Why is raw 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.

What is spoilage?

There are two types. Oxidation is caused by compounds in meat combining with oxygen and changing the meat's smell, flavor, and color. Badly oxidized meat is called rancid. But oxidized meat is usually not dangerous. The other type of spoilage is bacterial or viral spoilage, and it is very dangerous. There are several commonly occurring bacteria in food that can spoil it, such as are Bacillus cereus, Campylobacter jejuni, Clostridium botulinum, Listeria monocytogenes, Salmonella, Shigella, Staphylococcus aureus, and STECs (Shiga toxin-producing E-coli). Some of these bacteria will merely have you kneeling before the porcelain god, but others can maim or kill you. You can begin killing bacteria by cooking food to a safe temperature of 131°F or higher. At 165°F, bacteria are killed instantly. At 131°F, it can take hours. For more on bacterial kill temps, click here and scroll down.

Why is meat in my fridge is turning brown?

At first, oxygen reacts with pigments to turn meat red. After a while, the meat starts to oxidize, which turns it brown, the same way an apple or potato turns brown.

Why does my meat shine like a rainbow?

It is simply a fluke of lighting that strikes the surface just the right way when the surface has been cut on a certain angle. Strictly refraction, not bacteria or an oil slick.

Why is my meat green?

Bad bacteria. Throw it out.

Why are 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 dissipate within a few minutes. If it still smells funny, then chances are it is funny. Throw it out. Remember: when in doubt, throw it out!

What are those boogers coming out of my burgers and my salmon?