SOME SCIENCE OF COOKING

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Each year, you’ll hear that, in order to keep the bowl of guacamole green all during the Super Bowl, just stick an avocado pit in the center of the mash.

As if the big black seed were like the plinth in “2001: A Space Odyssey,” giving off some sort of aura or energy vibe to keep the guac from oxidizing and turning UPS-brown.

You’ll find that it doesn’t work that way. Oh, right underneath the pit, but just there, the indentation will be as green as could be because the pit has kept air away from the guacamole. Any barrier to air (oxygen) foils oxidation (browning).

Or perhaps you’re in luck and your guacamole stays green for a while because you mixed in a good amount of acidic elements such as lime juice and tomato bits. Acidity also inhibits oxidation.

But the plinth didn’t.

Knowing some science—from biology, chemistry, even physics—can help in the kitchen just as much as keeping your knives sharp. Here are a few other laws of nature for things culinary.

• I always thought that three bags of baby spinach wilted into a handful in the skillet because spinach was mostly water. All I did was evaporate that and—poof!—instant side dish. I’ve since learned that spinach is up to 70 percent air. Its leaves may resemble paper but they’re more like sponges. Cooking it pretty much just deflates it.

• The browning enzymes in basil leaves will discolor or blacken both the ingredients in pesto and the pasta served with pesto even more quickly than guacamole browns, in a matter of a couple of minutes. Forestall at least the pasta from looking drab by boiling it in acidulated water (about 1/4 cup lemon juice per quart of water). Neither the pasta nor the pesto will taste lemony because the water doesn’t permeate the noodles that far. Again, acidity prevents browning.

• Oil that might sputter in the sauté pan spots my eyeglasses—but on the back of the lenses, not the front, where I assume the oil would travel. But, no, heat conduction from the stove wafts hot air up and over my head and, along with it, the molecules of oil. They drop onto my eyeglasses from above and by the rear. So, I wear a baseball cap at the stove and they land on it and its lid instead, not on my lenses.

• I always thought it stupid, that advice to wipe or brush mushrooms of their dirt instead of rinsing them, the reason given that they would soak up the rinse water and get soggy. But mushrooms are already 90 percent water and rinsing only splashes water on the outsides of the shrooms. True enough, as long as you’re quick about it (just a minute or so), no rinse water unwelcomingly “permeates” the mushrooms.

• Lidding the pot when bringing to the boil a large volume of water (say, a gallon for pasta) makes sense and saves energy. That’s because you prevent evaporation, a synonym for cooling, and a counterforce to the heat that you want to achieve. But you don’t need to lid the pot from the get-go, only when the water is hot enough for poaching (around 160 degrees). That’s when the water’s surface begins actively to evaporate.

• Many marinades contain liquids high in acidity—wine, pineapple or citrus juice, vinegar, and the like—on the assumption that acidity is what will “break down and tenderize,” not to say flavor, the tough proteins or musculature of meat. What really osmoses into the meat is salt (especially salt water or brine) because it’s salt that restructures and untangles protein strands, not acidity. Acidity works only on the surface of meat and, furthermore, if set too long, makes meat (and especially fowl and fish) mushy.

• Barbecue cooks will say that they use tongs, instead of forks, to turn meat because piercing meat “will leak out the juices.” That’s not true. Almost all the moisture lost in a piece of heated (grilled, pan-fried, broiled) meat is the result of muscle fibers contracting and squeezing out their juices. Poking a wet sponge doesn’t leak out moisture from it any more than a barbecue fork does the same to its steak.

• Finally, here’s a cool trick (and also a nerd alert): Fish spoils faster than land meat because the pH of its flesh is around 7, a ripe environment for bacterial growth. (And, note, those piscine bacteria are already comfortable with cold living, so refrigeration is just a trade-out.) A compound present in nearly all fish called trimethylamine oxide (TMAO) is odorless when a fish is alive. But once the fish is killed, bacteria transform TMAO into simple trimethylamine (TMA), the source of that “fishy” odor. It isn’t bad or dangerous, just smelly.

• But because milk casein binds to TMA, a 20-minute cold soak in milk flushes out the TMA. Or, alternatively, a squeeze of lemon juice, an acid, neutralizes TMA, a weak alkali, by forming an odorless salt called—big word alert—trimethylammonium citrate. So, that’s why all the lemon wedges at seafood restaurants. Well, one reason; plus, they taste great too.

The recipe here includes both a meat marinade (mostly for allowing salt to imbed flavors) and grilling instructions, for which you may use either barbecue tongs or a fork.

One way to serve smoked and grilled pork belly is in large cubes or chunks.

RECIPE: Smoked and Grilled Pork Belly, Porchetta-style
You may order ahead pork belly in one piece from your butcher. Also, many Latino, Korean and some other Asian markets stock it on hand. Serves 6 or more.

Ingredients
1 5-pound square of pork belly, skin on
1/4 cup moderately fruity extra virgin olive oil
1/4 cup medium-coarse sea or kosher salt
2 tablespoons freshly cracked black pepper
1/4 cup fresh rosemary leaves (or 1/4 cup fresh thyme leaves, or mix of the two)
1/4 cup fennel fronds
2 tablespoons fennel seeds
2 teaspoons red pepper flakes
6 cloves garlic
Zest of 1 large or 2 small lemons

Directions
Make a paste of all the ingredients except the pork, either using a food processor or a mortar and pestle (or a molcajete). Set aside to flavor itself for an hour.

Wash the pork belly and dry with paper towels. Trim it of any excess fat on the non-skin side. Lay the pork with the skin side up and gently but thoroughly score the skin into 1-inch wide strips, using a very sharp knife or (the better implement) a single-edged razor, being cautious to cut through the skin and just into the fat only, not getting as far as any meat or muscle. Then make 1 perpendicular cut midway the entire width of the slab.

Slather the flavoring paste all over the pork, on both sides, pushing some of the paste into the slits made with the knife or razor. Either roll it up and place in a thick zippered plastic bag, or cover it with plastic wrap on a non-reactive plate, and place in the refrigerator overnight or for at least 10 hours. If feasible, you might turn and massage it once or twice.

When ready to cook, allow the pork to come to room temperature and remove most of the flavoring paste, either by shaking it free or brushing it off. Prepare a grill that has a cover and that allows for both direct as well as indirect cooking.

The first phase of the cooking will take about 6 hours and should be conducted at a temperature inside the grill between 250-275 degrees. Smoke and slowly cook the pork belly using the indirect method (that is, with the heat under but off to the side of the meat), skin side up the entire time. You might find useful a metal grill basket in which to place the pork. Also, because a fair amount of fat will melt away, something under the pork to catch that. Some grills also may require you to add a few pieces of charcoal every hour or so in order to maintain the heat.

When the thickest part of the belly reaches an internal temperature of 190 degrees (be sure to insert the probe at an angle), remove the pork belly and keep it warm.

The second stage of the cooking requires far less time but much greater heat, upwards of 475 degrees.

Construct a fire using the direct method, that is, with the heat under the grate and the meat. (If using flame or charcoal, you may need to scrape down your grill grate and build another fire.) Crisp both sides of the pork belly by grilling each side for 5 minutes apiece, beginning with the skin side down, then the other side. Because dripping fat will cause flare-ups that will char either side and render it bitter, cover the grill during both sears.

Remove the belly to a cutting board and let it rest, uncovered, for 15 minutes. You may slice the belly as you wish: into long thick slices the length of the slab (slicing along the original scoring, for example), or into cubes or chunks. The skin and edges may have crisped into cracklings or burnt-ends and will be fought over.

Serve with grilled vegetables or any number of other side foods.

With a sticky-sweet glaze: Omit the flavoring paste and instead season liberally and marinate overnight with a high-salt dry rub or adobo of your choosing. Follow all other directions. Just before the two final high-heat sears, slather onto both sides a glaze made from 1/2 cup each soy sauce and honey.

As samgyeopsal (Korean grilled pork belly): Omit the recipe’s flavoring paste. Use instead a paste made of 1/4 cup soy sauce or tamari, 3 tablespoons gochujang (Korean cooking paste made of red chiles, fermented soybeans and rice flour), 6 cloves of garlic, 2 tablespoons black pepper, 2 tablespoons sugar, 1 tablespoon miso paste and 1/4 cups chopped scallions (white and light green parts only). Follow all other directions.

With hoisin, lime, ginger and chile glaze: Omit the flavoring paste and instead season liberally and marinate overnight with a high-salt dry rub or adobo of your choosing. Follow all other directions. Just before the two final high-heat sears, slather onto both sides a glaze made from 1/2 cup hoisin sauce, 2 tablespoons each fresh lime juice and Thai sweet chile paste (or sambal) and 1 teaspoon freshly grated ginger.