Cooking for Geeks: Real Science, Great Hacks, and Good Food (35 page)

Most discussions of cooking are structured around the different heat transfer methods listed at the beginning of this chapter. Instead of looking at sources of heat, the rest of this chapter is going to take a different approach and talk about what reactions happen when each of the critical temperatures in the following table is reached, briefly touching on cooking techniques that relate to each temperature as they come up.

Chances are, you haven’t given much thought to the chemical reactions that happen to a piece of meat when the animal supplying it is slaughtered. The primary change is, to put it bluntly, that the animal is dead, meaning the circulatory system is no longer supplying the muscle tissue with glycogen from the liver or oxygen-carrying blood. Without oxygen, the cells in the muscle die, and preexisting glycogen in the muscle tissue dissipates, causing the thick and thin myofilaments in the muscle to fire off and bind together (resulting in the state called
rigor mortis
).

Denaturation temperatures of various types of proteins (top portion) and standard doneness levels (bottom portion).

Somewhere around 8 to 24 hours later, the glycogen supply is exhausted and enzymes naturally present in the meat begin to break down the bonds created during rigor mortis (
postmortem proteolysis
). Butchering before this process has run its course will affect the texture of the meat. Sensory panels have found that chicken breasts cut off the carcass before rigor mortis was over have a tougher texture than meat left on the bone longer. And since time is money, much mass-produced meat is slaughtered and then butchered straightaway. (I
knew
there was a reason why roasted whole birds taste better!)

Proteins in meat can be divided into three general categories: myofibrillar proteins (found in muscle tissue, these enable muscles to contract), stromal proteins (connective tissue, including tendons, that provide structure), and sarcoplasmic proteins (e.g., blood). We’ll talk about myofibrillar proteins here and save the stromal proteins for the section on collagen later in the chapter. (We’re going to ignore sarcoplasmic proteins altogether, because understanding them doesn’t help in cooking many dishes, blood-thickened soups aside.)

Muscle tissue is primarily composed of only a few types of proteins, with myosin and actin being the two most important types in cooking. About two-thirds of the proteins in mammals are myofibrillar proteins. The amount of actin and myosin differs by animal type and region. Fish, for example, are made up of roughly twice as much of these proteins as mammals.

Lean meat is mostly water (65–80%), protein (16–22%), and fat (1.5–13%), with sugars such as glycogen (0.5–1.3%) and minerals (1%) contributing only a minor amount of the mass. When it comes to cooking a piece of fish or meat, the key to success is to understand how to manipulate the proteins and fats. Although fats can be a significant portion of the mass, they are relatively easy to manage, because they don’t provide toughness. This leaves proteins as the key variable in cooking meats.

Of the proteins present in meat, myosin and actin are the most important from a culinary texture perspective. If you take only one thing away from this section, let it be this: denatured myosin = yummy; denatured actin = yucky. Dry, overcooked meats aren’t tough because of lack of water inside the meat; they’re tough because on a microscopic level, the actin proteins have denatured and squeezed out liquid in the muscle fibers. Myosin in fish begins to noticeably denature at temperatures as low as 104°F / 40°C; actin denatures at around 140°F / 60°C. In land animals, which have to survive warmer environments and heat waves, myosin denatures in the range of 122–140°F / 50–60°C (depending on exposure time, pH, etc.) while actin denatures at around 150–163°F / 66–73°C.

Food scientists have determined through empirical research (“total chewing work” and “total texture preference” being my favorite terms) that the optimal texture of cooked meats occurs when they are cooked to 140–153°F / 60–67°C, the range in which myosin and collagen will have denatured but actin will remain in its native form. In this temperature range, red meat has a pinkish color and the juices run dark red.

The texture of some cuts of meat can be improved by tenderizing. Marinades and brines chemically tenderize the flesh, either enzymatically (examples include bromelain, an enzyme found in pineapple, and zingibain, found in fresh ginger) or as a solvent (some proteins are soluble in salt solutions). Dry aging steaks works by giving enzymes naturally present in the meat time to break down the structure of collagen and muscle fibers. Dry aging will affect texture for at least the first seven days. Dry aging also changes the flavor of the meat: less aged beef tastes more metallic, more aged tastes gamier. Which is “better” is a matter of personal taste preference. (Perhaps some of us are physiologically more sensitive to metallic tastes.) Retail cuts are typically 5 to 7 days old, but some restaurants use meat aged 14 to 21 days.

Then there are the mechanical methods for “tenderizing,” which aren’t actually so much tenderizing as they are masking toughness: for example, slicing muscle fibers against the grain thinly, as is done with beef carpaccio and London broil, or literally grinding the meat, as is done for hamburger meat. (Some industrial meat processors “tenderize” meat by microscopically slicing it using very thin needles, a method called jacquarding.) Applying heat to meats “tenderizes” them by physically altering the proteins on the microscopic scale: as the proteins denature, they loosen up and uncurl. In addition to denaturing, upon uncurling, newly exposed regions of one protein can come into contact with regions of another protein and form a bond, allowing them to link to each other. This process is called
coagulation
, and while it typically occurs in cooking that involves protein denaturation, it is a separate phenomenon.

Temperatures required for various levels of doneness. Note that seafood cooked very rare or medium rare and chicken cooked medium must be held for a sufficiently long period of time at the stated temperature in order to be properly pasteurized. See the section on
Sous Vide Cooking
in
Chapter 7
for time and temperature charts.

Salmon Poached in Olive Oil

Fish, such as salmon and Atlantic char, becomes dry and loses its delicate flavor when cooked too hot. The trick with poaching fish is to not overcook it. Poaching fish is an easy way to control the rate of heat being applied, and it is amazingly easy and tasty.

Place a fillet of fish, skin side down, in an oven-safe bowl just large enough for the fish to fit. Sprinkle a small amount of salt on top of fish. Cover with olive oil until the fillet is submerged. Using a bowl that “just fits” the fish will cut down on the amount of olive oil needed.

Place into a preheated oven, set to medium heat (325–375°F / 160–190°C).

Use a probe thermometer set to beep at 115°F / 46°C and remove the fish when the thermometer goes off, letting carryover bring the temperature up a few more degrees.

Note

Consider this fish as raw/undercooked. See
Chapter 7
’s section on sous vide cooking for a discussion on pasteurization and time-at-temperature rules.

Notes

• Try serving on top of a portion of brown or wild rice and spooning sautéed leeks, onions, and mushrooms on top. (A squirt of orange juice in the leeks is really good.) Or serve with string beans sautéed with red pepper flakes and white rice, with a splash of soy sauce drizzled on top.
  
• Salmon contains a protein, albumin, that generates a white congealed mess on the outside of the flesh, as shown on the bottom piece in the following photo. This is the same protein that leeches out of hamburgers and other meats, typically forming slightly gray “blobs” on the surface. You can avoid this by brining the fish in a 5–10% salt solution (by weight) for 20 minutes, which will set the proteins. The top piece in the first photo below was brined; you can see the difference.
  

Salmon contains a protein, albumin, that is expressed out of the flesh and leads to an unsightly, curd-like layer forming on the surface of the fish when poached, as shown in the bottom piece in this photo.

If your fish doesn’t fit in your pan, you can fold the tail bit over in a pinch, or cut it and poach it face down. This won’t win you any Foodie Points, but as long as you don’t take a photo and publish it in a book, who’s going to know?