Cooking for Geeks: Real Science, Great Hacks, and Good Food
Page 28
3 tablespoons (40g) heavy cream
½ cup (50g) grated mozzarella cheese
4 teaspoons (20g) butter
Create a "well" in the center of the ingredients by pushing the food into a ring around the edges of the bowl. Crack two eggs into the well, add a pinch of salt and some fresh ground pepper, cover with aluminum foil, and bake in a preheated oven set to 350°F / 180°C until the egg is set, about 25 minutes. (You can use a probe thermometer set to beep at 140°F / 60°C.) Try adding some crushed red pepper flakes to the breakfast version or sriracha sauce to the dinner version.
Pasteurized Eggs
While salmonella is quite rare in uncooked eggs, with estimates being somewhere around 1 in 10,000 to 20,000 eggs carrying the bacteria, it does occur in the laying hen populations of North America. If you’re cracking a few dozen eggs into a bowl for an omelet brunch at your local hacker house every week, let’s just say that odds are you’ll eventually crack a bad egg. Luckily, this isn’t a problem if those eggs are properly cooked and cross-contamination is avoided.
The real risk for salmonella in eggs is in dishes that use undercooked eggs that are then served to at-risk populations (e.g., infants, pregnant women, elderly or immunocompromised people). If you’re making a dish that contains raw or undercooked eggs—Caesar salad, homemade eggnog, mayonnaise, raw cookie dough—and want to serve that dish somewhere where there might be at-risk individuals, you can pasteurize the eggs (assuming your local store doesn’t happen to carry pasteurized eggs, but most don’t). Pasteurized eggs do taste a little different, and the whites take longer to whip into a foam, so don’t expect them to be identical to their raw counterparts.
Since salmonella begins to die at a noticeable rate around 136°F / 58°C and the proteins in eggs don’t begin to denature until above 141°F / 61°C, you can pasteurize eggs to reduce the quantity of salmonella, should it be present, to an acceptable level by holding the egg at a temperature between these two points. The FDA requires a 10,000-fold reduction (5 log10 in food safety lingo), which can be achieved by holding the egg at 141°F / 61°C for 3.5 minutes (according to Margaret McWilliams’s Foods: Experimental Perspectives, Fifth Edition, from Pearson Publishing). Most consumers won’t have the necessary hardware to do this at home, but if you do have a sous vide setup, as described in Chapter 7, you’re golden.
The 60-Minute Slow-Cooked Egg
Going back to our earlier discussion of time and temperature, when food is left in an environment long enough, its temperature will come to match that of its environment. Therefore, if we immerse an egg in water held at 145°F / 62.7°C, it follows that the proteins in the white and the yolk that denature at or below that temperature will denature and coagulate, and those that denature above that temperature will remain unaltered.
The added benefit of this method is that the egg cannot overcook. "Cooking" is effectively the occurrence of chemical reactions in the food at different temperature points, and holding the egg at 145°F / 62.7°C will not trigger any reactions that don’t occur until higher temperatures are reached. This is the fundamental concept of sous vide cooking. We’ll cover the details of sous vide in Chapter 7, so you may want to take a peek at that chapter now or make a mental note to come back to this section when you get there. For a sous vide–style cooked egg, immerse an egg in water that is maintained at 145°F / 62.7°C for one hour. As you’ll see, sous vide cooking has some incredible properties that greatly simplify the time and temperature rule.
Note
Your average, run-of-the-mill (or is that run-of-the-yard?) chicken laid only 84 eggs per year a century ago. By the turn of the millennium, improvements in breeding and feed had pushed this number up to 292 eggs per year—almost 3.5 times more. And, no, science has not yet figured out which came first.
154°F / 68°C: Collagen (Type I) Denatures
An animal’s connective tissues provide structure and support for the muscles and organs in its body. You can think of most connective tissues—loose fascia and ligaments between muscles as well as other structures such as tendons and bones—as a bit like steel reinforcement: they don’t actively contract like muscle tissue, but they provide structure against which muscles can pull and contract.
Temperatures related to collagen hydrolysis and the resulting gelatin.
The most common type of protein in connective tissue is collagen, and while there are several types of collagen in animals, from a culinary perspective, the main chemical difference between the different types of collagen is the temperature at which they denature. In cooking, collagen shows up in two different ways: either as discrete chunks (e.g., tendons, silverskin) outside of the muscle, or as a network that runs through the muscle. Regardless of its location, collagen is tough (it provides structure, after all) and becomes palatable only given sufficient time at sufficiently high temperatures.
It’s easy to deal with collagen that shows up as discrete pieces: get rid of it by cutting it off. For cuts of meats that have a thin layer of connective tissue on them (called silverskin, presumably because of its somewhat iridescent appearance), cut off as much as possible and discard it. Beef tenderloin cuts commonly have a side with this layer; trim off as much as possible before cooking.
Chicken breasts also have a small but noticeable tendon connected to the chicken tenderloin. Uncooked, it’s a pearlescent white ribbon. After cooking, it turns into that small white rubber-band-like thing that you can chew on endlessly yet never get any satisfaction from. Generally, this type of collagen is easy to spot, and if you miss it, it’s easy to notice while eating and can be left on the plate.
However, for the other kind of collagen found in some cuts of meat—collagen that forms a 3D network through the muscle tissue—the only way to remove it is to convert it to gelatin via long, slow cooking methods. Unlike muscle proteins—which in cooking are either in a native (i.e., as they are in the animal), denatured, or hydrolyzed state—collagen, once hydrolyzed, can enter a coagulated (gelled) state. This property opens up an entirely new world of possibilities, because gelatin gives meats a lubricious, tender quality and provides a lip-smacking goodness.
In its native form, collagen is like a rope: it’s a linear molecule composed of three different strands that are twisted together. The three strands are held together by weak secondary bonds (but there are a lot of them!) and stabilized by a small number of crosslinks, which are stronger covalent bonds.
Collagen in its native form is a triple helix, held together in its helical structure by secondary bonds (left) and stabilized by crosslinks. Under heat, the secondary bonds break and the protein becomes denatured, but the crosslinks between the strands continue to hold the structure together (second from left). Given sufficient heat and time, the strands in the triple helix themselves break down via hydrolysis (third from left) and, upon cooling, convert to a loose network of molecules (right) that retains water (a gel).
Note
Covalent bonds are bonds where the electrons from an atom in one location are shared with another atom.
In addition to being crosslinked, the strands also form a helical structure because of secondary bonds between different regions of the same molecules. You can think of it something like a braided rope, where each strand wraps around the other two strands. It has a "curl" to it because the internal structure finds its optimal resting place in that shape.
Under the right conditions—usually, exposure to heat or the right kinds of acids—the native form of collagen denatures, losing its linear structure and untwisting into a random mess. With the addition of sufficient heat, the molecules in the structure will vibrate enough to overcome the electromagnetic energy that caused the structure to twist up in the first place, leading it to lose its helical structure and denature.
Acids can also denature the collagen protein: their chemical properties provide the necessary electromagnetic pull to disrupt the secondary bonds of the helical structure. It’s only the twisting that goes away during denaturin
g in collagen; the crosslinks remain in place and the strands remain intact. In this form, collagen is like rubber—it actually is a rubber from a material science point of view—and for this reason, you’ll find its texture, well, rubbery.
Given even more heat or acid, though, the collagen structure undergoes another transformation: the strands themselves get chopped up and lose their backbone, and at this point the collagen has no real large-scale structure left. This reaction is called hydrolysis: thermal hydrolysis in the case of heat, acid hydrolysis in the case of, you guessed it, acid. (Think ceviche. See the section on acids in Chapter 6 for more.)
It’s possible to break up the collagen chemically, too: lysosomal enzymes will attack the structure and "break the covalent bonds" in chem-speak, but this isn’t so useful to know in the kitchen.
Note
For fun, try marinating a chunk of meat in papaya, which contains an enzyme, papain, that acts as a meat tenderizer by hydrolyzing collagen.
One piece of information that is critical to understand in the kitchen, however, is that hydrolysis takes time. The structure has to literally untwist and break up, and due to the amount of energy needed to break the bonds and the stochastic processes involved, this reaction takes longer than simply denaturing the protein.
Hydrolyzing collagen not only breaks down the rubbery texture of the denatured structure, but also converts a portion of it to gelatin. When the collagen hydrolyzes, it breaks into variously sized pieces, the smaller of which are able to dissolve into the surrounding liquid, creating gelatin. It’s this gelatin that gives dishes such as braised ox tail, slow-cooked short ribs, and duck confit their distinctive mouthfeel.
Since these dishes rely on gelatin for providing that wonderful texture, they need to be made with high-collagen cuts of meat. Trying to make a beef stew with lean cuts will result in tough, dry meat. The actin proteins will denature (recall that this occurs at temperatures of 150–163°F / 66–73°C), but the gelatin won’t be present in the muscle tissue to mask the dryness and toughness brought about by the denatured actin. Don’t try to "upgrade" your beef stew with a more expensive cut of meat; it won’t work!
"Great," you might be thinking, "but how does any of this tell me whether I need to slow-cook a piece of meat?" Think about the piece of meat (or fish or poultry) that you’re working with and consider what part of the animal it comes from. For a land-based animal, those regions of the animal that bear weight generally have higher levels of collagen. This should make sense: because the weight-bearing portions have a higher load, they need more structure, so they’ll have more connective tissue. This isn’t a perfect rule of thumb, though, and cuts of meat generally have more than one muscle group in them.
For animals like fish, which don’t have to support their weight on land, the collagen levels are much lower. Squid and octopus are notable exceptions to this weight-bearing rule, because their collagen provides the equivalent support that bone structures do for fish.
When cooking a piece of meat, if it’s from a part that is responsible for supporting the animal’s weight (primarily muscles in the chuck, rib, brisket, and round), it’ll probably be higher in collagen and thus need a longer cooking time.
Note
Older animals have higher levels of collagen. As animals age, the collagen structure has more time to form additional crosslinks between the strands in the collagen helix, resulting in increased toughness. This is why older chickens, for example, are traditionally cooked in long, slow roasts. (The French go so far as to use different words for old versus young chickens: poule instead of poulet.) Most commercial meat, however, is young at time of slaughter, so the age of the animal is no longer an important factor.
The other easy rule of thumb for collagen levels is to look at the relative price of the meat: because high-collagen cuts require more work to cook and come out with a generally drier texture, people tend to favor other cuts, so the high-collagen cuts are cheaper.
Squid Bruschetta
Squid was a culinary mystery to me for a long time. You either cook it for a few minutes or an hour; anywhere in between, and it becomes tough, like chewing on rubber bands. (Not that I chew on rubber bands often enough to say what that’s like.) Why is this?
The collagen in squid and octopus is enjoyable in either its native state or hydrolyzed state, but not in its denatured state. It takes a few minutes to denature, so with just a quick pan sear it remains in its native state (tossed with some fresh tomatoes and dropped on top of bruschetta, it’s delicious). And hydrolysis takes hours to occur, so a slowly simmered braised octopus turns out fine. Braising it in tomatoes further helps by dropping the pH levels, which accelerates the hydrolysis process.
To make a simple squid bruschetta, start by preparing a loaf of French or Italian bread by slicing it into ½″ (1 cm) slices. You can create larger slices by cutting on a bias. (Save the triangular end piece for munching on when no one is looking.) Lightly coat both sides of the bread with olive oil (this is normally done with a pastry brush, but if you don’t have one, you can either fold up a paper towel and "brush" with it or pour olive oil onto a plate and briefly dip the bread into the oil). Toast the bread. A broiler works best (the slices of bread should be 4–6″ / 10–15 cm from the heat). Flip as soon as they begin to turn golden brown. If you don’t have a broiler, you can use an oven set to 400°F / 200°C. For small batches, a toaster also works.
Once your bread is toasted, place it on a plate and store it in the oven (with the heat off) so that it remains warm.
Prepare the squid:
1 lb (500g) squid (either a mix of bodies and tentacles or just bodies)
Slice the squid with a knife or, better yet, cut it into bite-sized pieces using kitchen shears.
Bring a sauté pan up to medium heat. You want the pan hot enough so that the squid will quickly come to temperature. Add a small amount of olive oil—enough to coat the pan thinly when swirled—and drop the squid into the pan.
Use a wooden spoon or silicone spatula to stir the squid. Take note when it starts to turn white—it should become subtly less translucent—and cook for another 30 seconds or so. Add to the pan and toss to combine:
1 cup (250g) diced tomato (about 2 medium tomatoes, seeds removed)
1 tablespoon (2g) fresh herbs such as oregano or parsley
¼ teaspoon sea salt
Ground pepper to taste
Transfer squid and tomato topping to a bowl and serve with toasted bread.
Try using a pair of kitchen shears to snip the squid into small pieces directly into a hot pan. Add tomatoes and herbs, toss, and serve.
Slow-Cooked Short Ribs
Short ribs and other high-collagen cuts of meat aren’t difficult to work with, they just require time at temperature (collagen takes many hours to hydrolyze). The trick is to cook this type of meat "low and slow"—for a long time at low temperature. Too cold, and the collagen won’t break down; too hot, and the water in the meat will evaporate, drying it out. Using a slow cooker cooks the meat in the ideal temperature range. After all, this is what they’re designed for!
This is an intentionally easy recipe, but don’t let this fool you: slow-cooked meats can be amazingly good, and if you’re cooking for a dinner party, they make for easy work when you go to assemble the dinner. If you have a rice cooker, check to see if it has a "slow-cook" setting. In this mode, the rice cooker will heat foods to a temperature typically between 170–190°F / 77–88°C, which is warm enough to be safe from bacterial contamination and cool enough to not steam-dry the meat.
Pour a bottle of barbeque sauce into the bowl of the rice cooker or slow cooker. Add the short ribs, arranging them in a layer so that the barbeque sauce covers the meat.
Slow-cook for at least four hours (longer is fine). Try starting this in the morning before going to work—the slow cooker will keep the food safe, and the extra time will help ensure that the collagen is fully dissolved.
Notes
Ideally,
you should pan sear the short ribs (in a cast iron pan) for a minute or two before cooking. As discussed at the beginning of this chapter, this will cause browning reactions, bringing a richness to the final product.
Keep in mind the danger zone rule covered earlier. Don’t load up a slow cooker with so much cold meat that the cooker will be unable to raise the temperature above 140°F / 60°C within a two-hour period.
Try adding other ingredients to the sauce, or making your own sauce if you like. I’ll often pour a tablespoon or so of wine or port into the empty BBQ sauce jar to "rinse out" the thick sauce, then pour the port-sauce slurry into the slow cooker.
Duck Confit
Duck confit—duck legs cooked in fat—tastes entirely different from duck cooked almost any other way. It’s like bacon and pork—to quote Homer Simpson, they’re from "some wonderful, magical animal." Good duck confit is succulent, flavorful, tender, mouth-watering, and perhaps a bit salty. Even if you’re not otherwise a fan of duck, give duck confit a chance.
As you can probably tell, I’m a pragmatic cook. Traditional recipes for duck confit prescribe a long, drawn-out affair, which is fine for a leisurely Sunday afternoon spent in the company of friends and a bottle of good wine, but doesn’t line up well with my idea of keeping things simple.
Cooking duck "confit-style" is all about converting tough collagen proteins into gelatin. While this isn’t a fast chemical reaction, it’s a simple one to trigger: hold the meat at a low temperature for long enough, and the collagen proteins denature and eventually hydrolyze.
The secret to duck confit is in the time and temperature, not the actual cooking technique. The upshot? You can make duck confit in a slow cooker or in an oven set at an ultra-low temperature. The fat that the duck is cooked in doesn’t matter either; some experiments have shown that duck confit cooked in water and then coated in oil is indistinguishable from traditionally cooked duck confit. Regardless, definitely skip the exotic block of duck fat; duck legs are expensive enough as it is.