Grilling
Part II - Understanding Meat

Meat is the muscle of a dead animal; fish flesh is the muscle of fish. So understanding meat and fish flesh involves understanding muscle.

Muscle is of three basic types: striated, cardiac, and smooth. Cardiac is the muscle of the heart, and smooth muscle is the muscle of involuntary organs, such as the intestines. Our concern is striated muscle, the muscle animal and fish control voluntarily that moves their skeletal system.

Striated muscle consists of three basic parts: muscle fibers, connective tissue, and fat. I will explain each. However, it is very important to note that within the muscle fiber and connective tissue of animals and fish is a tremendous amount of water. Generally the muscle is 75% to 80% water. Dry heat cooking drives that water from the meat in the form of steam and expelled juice. Since grilling is a form of dry heat cooking, as a piece of meat or fish is grilled, its moisture content and juiciness is reduced, and along with it, its size. Over grilling meat and fish toughens it and dries it out, diminishing its gustatory appeal.

Muscle Fibers
Striated muscles consist of a myriad of very fine bands of muscle fibers. Each muscle fiber is wrapped in a thin connective tissue sheath. Individual fibers are then bound together into bundles, which again are wrapped in a thicker connective tissue. Within the bundles, in among the individual muscle fibers, are capillaries, nerve branches, and fat cells; these fat cells are known as "marbling." Several muscle bundles are themselves grouped together into a larger bundle which again is covered by connective tissue. This is the whole muscle. Large fat deposits often cover a whole muscle. The fat covering is called "adipose tissue."

We need to now go back to the individual muscle fibers and discuss them briefly. Each muscle fiber consists of 1,000 to 2,000 tiny fibrils, called "myofibrils." The myofibrils are made up of proteins, specifically two fibrous proteins: actin and myosin. The muscle proteins need water to operate; for that reason they are surrounded by water. The actual muscle fibers are about 20% protein and 75% water.

Muscle fibers: primarily the proteins actin and myosin, and water.

The size and length of muscle fibers is one determinant of tenderness and toughness of meat. Meat with thin fibers united into small bundles has a fine grain and tends to be tender. An example is the tenderloin or fillet cut of beef. Meat with thick fibers united into large bundles has a coarse grain and tends to be tough. An example is flank steak, also known as London broil. You can see and feel the difference between the fine-grained and coarse-grained meats. One reason fish flesh is tender is because it has very short bundles of muscle fibers.

Connective Tissue
Connective tissue in meat is a cause of toughness. It supports the muscle so it has a rigid structure. In short, the more connective tissue, the tougher the meat. Also the older the muscle, the more rigid the connective tissue.

Connective tissue is made up of two kinds of protein: collagen and elastin. Collagen is white; elastin is yellow. Elastin has tremendous tensile strength; that means it can be stretched with great force and not tear. Elastin is not soluble, and cannot be broken down by the heat used in cooking. It is made tender by pounding, grinding (ground beef), or slicing it into tiny lengths, as when London broil is sliced against the grain.

Fortunately, collagen is broken down by aging, acid, and cooking. With regard to aging, enzymes break collagen down slowly when the meat is refrigerated, more quickly at room temperature. Acids such as vinegar, tomato, and wine also break down collagen. With regard to cooking, when heated in the presence of water, the collagen protein loses its structure and becomes a gelatin-like substance. Since muscle is 75% water, there is usually water present to help convert collagen to soft, gelatinous material. (Collagen, by the way, is the source of gelatin, the main ingredient in aspic and Jell-O.) Meats with a lot of connective tissue, such as pot roast, are best cooked using added moisture at a low temperature for a good length of time: this will enable the collagen to break down and the meat to become tender. Braising is such a cooking method.

Connective tissue: the proteins collagen and elastin

The connective tissue in fish flesh is unique: it is very thin. It binds the muscle fibers of fish in stacks of short bundles called "myomeres." The stacks and the thin connective tissue give fish flesh its soft and flaky texture.

Fat
Fat both surrounds the muscle, called "adipose tissue," and is present within the muscle, known as "marbling." Fat has no water. The higher the percentage of fat in meat, the less water. However, fat contributes to the tenderness in meat. As fat heats, it becomes liquid or oil and lubricates the meat. The liquid fat is a major part of the perceived juiciness of cooked meat. Marbling also contributes to tenderness because it separates the muscle bundles. In addition, fat is very tasty; it is one of the main sources of flavor in meat.

Fish flesh is tender in part because the fat in fish is mostly liquid to begin with. It is what we know of as "fish oil." Fish oil is a very healthy kind of fat: omega-3 polyunsaturated fatty acid. It consists of two acids: iecosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Cooking Muscle
When muscle is exposed to heat between 104 and 122 degrees Fahrenheit, the proteins in the muscle fiber - actin and myosin - begin to break down, technically "denature." What does that mean? Proteins have a three-dimensional structure in which they curve back upon themselves, like a pretzel. This is called their "tertiary structure." Interactions between the amino acids of the protein hold the different parts of the protein in place. Heat causes those interactions to cease and the protein loses its normal shape. As a result, the protein begins to loose its ability to be dissolved in liquid. Between 150 degrees and 170 degrees, the proteins lose more of their shape; they shorten and toughen. Also, water is driven out of the muscle tissue compacting the proteins one against the other. The muscle tissue becomes firm and dry. At 160 degrees, meats are fully cooked.

When you cook a steak, you can feel the process of the proteins denaturing and compacting. At first when you push on the steak with your finger, it feels soft and pliable. As it cooks, you will feel more and more firmness. With experience, you can tell the doneness of a steak by feel. You can also see the water being pushed out of the steak. As it cooks, the water is driven away from the heat, so it will appear as bubbles of juice on the surface of the steak away from the radiant heat source; i.e., when grilling, the upper surface of the steak.

The collagen protein of connective tissue reacts very differently to heat. Between 122 and 160 degrees Fahrenheit, the collagen proteins shorten and the connective tissue shrinks. But over 160 degrees, the collagen breaks down into a gelatin-like substance; it becomes a gel.

There is trade off, then, between muscle firmness and complete collagen breakdown. The heat (160 degrees) that converts collagen to a soft substance also toughens and dries out the muscle fiber. For that reason, meat, such as tenderloin, which has a low amount of connective tissue, should be cooked rare (130 degrees) to medium (140 degrees). That way the cuts will be most tender. Meat high in connective tissue, such as pot roast, should be cooked slowly to well done (160 degrees) in added moisture to achieve complete collagen gelatinization. That way those cuts will be most tender. Fish flesh does not need to be cooked well done, because there is no tough connective tissue to break down.

Interior Temperatures: Rare 130º,  Medium 140º - 145º,  Well Done 160º

Note: the trichinosis parasite in pork is killed at 137 degrees Fahrenheit; pork is fully done at 160 degrees. Because of trichinosis, pork should be cooked to at least 150 degrees.  Poultry is usually cooked until well done.

As fat heats, it becomes a liquid lubricating the meat. However, overcooking will cause too much of the fat to leak out of the meat. Also, fat is volatile and burns easily. Controlled burning of bits of fat enhances flavor, but uncontrolled burning ruins it.

In short, heat kills harmful bacteria, turns solid fat to liquid, and at 160 degrees turns collagen into a gel, all good results. However, it also drives moisture out of meat, toughens the muscle fibers, and causes liquid fat to leak out of meat. Overcooking, thus, results in dry, tough meat. It is important, then, to cook each cut of meat the right amount for it to get maximum flavor and tenderness. Moreover, moisture resists heat. As moisture is driven out, the cooking of muscle fibers accelerates. Since grilled meats are usually fine grained, it is important not to overcook, even pork. To that end, it is crucial to watch carefully the final minutes of cooking.