Salt, Fat, Acid, Heat

by Samin Nosrat

  Water can also be a medium in which we cook other foods. At low temperatures, water is particularly gentle: water baths are ideal for cooking custards; and simmering, braising and poaching provide tough foods with the sustained low heat they need to develop tenderness.

  Heat water further, to 212°F at sea level, and it boils, giving us one of the most efficient—and quickest—ways to cook food. Boiling water is one of the most invaluable tools in the kitchen. It’s a simple way to gauge temperature without a thermometer. If you see bubbles roiling in a pot of water, you know that it’s reached 212°F. At this temperature, water can kill pathogenic bacteria. To be on the safe side, when reheating soupy leftovers or your freezer stash of chicken stock, make sure to bring them to a boil to kill bacteria that may have grown in the meantime.

  The Power of Steam

  As water is heated beyond 212°F, it transforms into steam, another of the kitchen’s most valuable visible cues. Let the sight of steam help you approximate temperature: as long as food is wet and giving off steam, its surface temperature probably isn’t hot enough to allow browning to begin. Remember, the reactions that cause food to brown—caramelization and the Maillard reaction—don’t begin until food reaches much higher temperatures. So, if water is present on the surface of a food, it can’t brown.

  Learn to make decisions in relationship to steam. Encourage steam to escape if you want temperatures to rise and food to brown. Contain and recycle steam with a lid to allow food to cook in a moist environment if you want to prevent or delay browning.

  Food piled up in a pan can affect steam levels in a pan by acting like a makeshift lid: both entrap steam. Trapped steam condenses and drips back down, keeping food moist and maintaining the temperature right around 212°F. At first, entrapped steam gently wilts food, and then it leads to sweating, which is a way to cook food through without allowing it to develop any color.

  Steam replaces some of the air contained in vegetables with water, which is why plants initially transform from opaque to translucent in color and reduce in volume as they cook. They also begin to intensify in flavor—a mountain of just-washed spinach becomes a molehill of wilted greens and a pan mounded full of sliced onions cooks down into a stewy, flavorful base for Silky Sweet Corn Soup.

  Pile chard leaves high above the sides of a pan and let steam cook the greens. Cover with a lid if you like, but stir once in a while with tongs to ensure even cooking, because even steam can’t navigate the labyrinth of greens as evenly as you might hope. The temperature at the bottom of the pan, closer to the heat source, will always be higher than the temperature above. Control steam in the oven when roasting or toasting foods using the same variables. How tightly a sheet pan of vegetables is packed is as much of a factor in even browning as the oven temperature. Let zucchini and peppers develop glorious sweetness and flavor by spreading them out so steam can escape and browning can begin sooner. Protect denser vegetables that take longer to cook, such as artichokes or cipollini onions, from browning too much before they can cook through by packing them tightly in a pan to entrap steam.

  Choose your cooking vessel based on how steam will move within and out of it. Pans with sloped or curved sides are better at allowing steam to escape than pans with straight sides. And the taller the sides of the pan or pot, the longer it will take steam to escape. Deep pots and pans are great for sweating onions and simmering soups, but less ideal for foods you aim to sear and brown quickly, such as scallops and steaks.

  Recall the osmosis that salt initiates, and weave that understanding into how you decide to use steam. Let salt do its work, drawing water out of food it touches, to help create steam when you want it in the pan. When the goal is to brown swiftly, wait to salt food until after it begins to crisp or salt far enough in advance to let osmosis occur, pat food dry, and then place into a hot pan. Use the former method for onions you want to sweat and keep translucent for cauliflower soup, and the latter for eggplant and zucchini you plan to grill or roast.

  Fat and Heat

  In Fat, I explained the main principles that will help you understand how Heat and Fat work together in good cooking. Like water, fat is both a basic component of food and a cooking medium. But fat and water are enemies: they don’t mix, and they respond very differently to heat.

  Fats are flexible; indeed, the broad range of temperatures fats can withstand allows us to achieve many different textures—crisp, flaky, tender, creamy, and light—that simply cannot be achieved without the proper relationship between Fat and Heat.

  When chilled, fats harden—and transform from liquids into solids. Solid fats such as butter and lard are a boon to pastry chefs, who can work them into doughs to achieve flakiness or whip air into them to achieve lightness. But picture the way greens cooked with bacon leave a trail of semisolid grease behind on the platter and you’ll see how this quality is less desirable when serving food containing animal fats that congeal at room temperature.

  Extended, gentle heat will transform, or render, solid animal fats into pure liquid fats such as pork lard or beef tallow. In slow-cooked meats such as Sage- and Honey-Smoked Chicken, rendering fats essentially bastes food from within, and this self-basting also explains the exuberantly moist texture of Slow-Roasted Salmon. The same gentle heat will cause butter’s emulsion to break and then clarify.

  At moderate temperatures, fat is an ideal gentle cooking medium, perfect for using in a cooking method called confit, which is essentially poaching in fat instead of water. Look ahead to recipes for Tomato, Tuna, and Chicken Confit to put this technique into practice.

  While water boils and vaporizes at 212°F, fats can climb to staggering temperatures well beyond that point before turning to smoke. As a result, since water and fat don’t mix, foods containing water (which is practically all foods) won’t dissolve in fat; instead the surfaces of foods exposed to very hot fats can climb to high enough temperatures to develop crisp textures as water evaporates.

  Fats are slow to cool and heat—in other words, it takes a lot of energy to heat or cool a unit of fat by even a few degrees. This is a boon to the amateur deep fryer; you can relax when frying Beer-Battered Fish, knowing you don’t have to act with lightning-quick reflexes when the temperature of the oil starts to rise or fall. If the fat gets too hot, just turn off the heat or carefully add a little more room-temperature oil. If the pot gets too cold, increase the heat and wait before adding more food. The same phenomenon will cause meats with large quantities of fat such as prime rib or pork loin roasts (or those sitting in fat, such as any of the confits mentioned above) to continue cooking slowly even when pulled from the heat.

  Carbohydrates and Heat

  Found primarily in foods made from plant sources, carbohydrates provide food with both structure and flavor. In Acid, I described three types of carbohydrates—cellulose, sugars, and pectin. Along with a fourth type of carbohydrate—starches—cellulose provides much of the bulk and texture of plant-derived foods, while sugars offer flavor. When heated, carbohydrates generally absorb water and break down.

  Understanding a bit of basic Plant Anatomy will help you determine how to cook various plant-derived foods. If fibrous or stringy is a word that comes to mind when you think of a particular fruit or vegetable, it’s rich in cellulose, a type of carbohydrate that isn’t broken down by heat. Cook cellulose-rich produce, such as collard greens, asparagus, or artichokes, until it absorbs enough water to become tender. Leaves have less cellulose fibers than stems or stalks, which is why kale and chard stems cook at a different rate than their leaves and ought to be stemmed and cooked separately, or simply staggered into the pot.

  Starches

  Give the starchiest parts of plants, including tubers such as potatoes and seeds such as dried beans, plenty of water and time over gentle heat to coax out their tenderness. Starches absorb liquid and swell or break down, so firm potatoes become delightfully creamy, impossibly hard chickpeas transform into buttery bites, and rice goes from indigestible to fluff
y and tender.

  Dry seeds, grains, and legumes, including rice, beans, barley, chickpeas, and wheatberries, generally need water and heat to make them edible. To protect the potential for life that they contain, seeds have evolved with tough sheaths that make them nearly impossible for us to digest unless we transform them in some way. Sometimes, this simply means removing the shell, as we do with sunflower and pumpkin seeds. For seeds that need to be cooked in order to become edible, this usually means adding water and heating them until they grow tender. Some starch-rich seeds, including dried shell beans, chickpeas, and hearty grains like barley benefit from an overnight soak, which gives them a head start at absorbing water. Consider it a sort of inactive cooking.

  Some grains are processed to remove some or all of this outer sheath—hence the difference between whole wheat and refined flour or brown and white rice. Without that tough exterior, processed grains cook much more quickly and have a longer shelf-life than their whole-grain counterparts. Ground, or milled, grains can be combined with water to make doughs and batters, which firm and set up with exposure to heat.

  The key to cooking starches properly is using the correct amount of water and heat. Use too little water or undercook starches and they will be dry and unpleasantly tough in the center. Cakes and bread baked with too little water are dry and crumbly. Undercooked pasta, beans, and rice are unpleasantly tough in the center. But use too much water or heat, or simply overcook starches, and they will be mushy (think limp noodles and soggy cakes and rice). Starches are eager to undergo browning and will burn easily if overcooked or exposed to too much heat. I kick myself when this happens—scorched grits at the bottom of an unwatched pot, or bread crumbs blackened after just 90 seconds of neglect in a hot oven.

  Sugars

  Odorless and colorless, sucrose, or sugar is the pure manifestation of sweetness. When exposed to heat, it melts. Mix granulated sugar with water and heat it to high temperatures to yield myriad confectionary delights with varied textures: marshmallows, meringues, fudge, nougat, butterscotch, brittle, toffee, pralines, and caramel candies.

  Working with hot sugar is one of the few temperature-specific endeavors in the kitchen, but it’s not a particularly difficult one. At about 290°F, a melted sugar syrup will yield a firm nougat, but just a ten-degree increase will yield toffee. The first time I made caramel candies I was too stingy to buy a twelve-dollar candy thermometer. I figured I could just eyeball the temperature. As a result, my caramels were so sticky that I ended up paying hundreds of dollars for dental work instead. Learn from my stubbornness and invest in a candy thermometer to help monitor temperatures when working with sugar (and use it for deep-frying, too!). Trust me, you’ll save money in the long run.

  At extremely high temperatures (340°F), sugar molecules begin to darken in color, in a process that isn’t entirely understood, as they decompose and reorganize into hundreds of new compounds, generating abundant new flavors. This is caramelization, and it’s one of the most essential ways heat affects flavor. In addition to producing acidic flavor compounds, caramelized sugars introduce a slew of new qualities and flavors, including bitter, fruity, caramel, nutty, sherry, and butterscotch.

  In addition to starches that can be broken down into sugars, fruits, vegetables, dairy, and some grains also contain natural simple sugars that can participate in the same reactions as table sugar when cooked. They grow sweeter with heat, and can even caramelize. As heat penetrates a boiling carrot, for example, its starches begin to break down into simple sugars. The cell walls enclosing these sugars begin to disintegrate. This frees the sugars to reach our taste buds more readily, making the cooked carrot taste far sweeter than its raw counterpart.

  The small amounts of sugars that most vegetables contain begin to disappear the moment they’re picked, which is why just-picked produce is so much more sweet and flavorful than store-bought. I’ve heard countless stories of Midwestern grandmothers putting the pot of water on to boil before sending the kids out to the garden to pick corn. Just a few minutes, they’d tell the kids, could mean a noticeable loss in sweetness. As it turns out, the grannies were right: just a few hours at room temperature can deprive starchy vegetables like corn and peas of half of their sugars. Potatoes, too, are at their sweetest when first harvested—hence the indescribable pleasure of boiled new potatoes topped with butter. As potatoes sit in storage all year, though, their sugars convert to starches. Fry newly dug potatoes, full of sugar, and they’ll burn before they can cook through. Instead, when making potato chips or fries, use starchy, older potatoes and rinse them of excess starches after slicing until the water runs clear. Only then will your fried potatoes emerge from hot oil of the fry pot crisp but not burnt.

  Pectin

  Another carbohydrate, pectin, is a kind of indigestible fiber, and I like to think of it as fruit- and vegetable-derived gelatin. Found primarily in the seeds and peels of citrus fruits, stone fruits, and apples, pectin functions as a gelling agent when combined with sugar and acid and exposed to heat. Its setting properties make possible fruit preserves and fruit pastes such as membrillo, the Spanish quince paste. From June Taylor, a champion of traditional British preserve-making methods, I learned to extract pectin from citrus into my marmalade. She taught me to place a couple handfuls of membranes and seeds into a cheesecloth pouch and cook it into the marmalade along with the fruit. When the preserves are partially cooked, I remove the bag, let it cool, and then massage it to coax out the pectin. The first time I did this, I was shocked to find that I could actually see the pectin—a milky white liquid. When, months later, I opened that jar of marmalade, the pectin’s effects were clear: the marmalade was set, not runny, and spread smoothly across my hot, buttered toast.

  Proteins and Heat

  It helps me to picture proteins as coiled threads floating around in water. This definition proves particularly useful when visualizing how temperature affects proteins. As with acid, when exposed to heat, the threads first denature, or unwind, and then clump together more tightly, or coagulate, entrapping pockets of water, to create structure in foods.

  Think of how heat transforms a chicken breast from flabby and watery to firm, tender, and moist when perfectly cooked. But apply too much heat and the protein clumps will continue to tighten, squeezing out the pockets of water. With its water expelled, the chicken becomes dry, stringy, and tough.

  This phenomenon is also apparent in scrambled eggs. Cook scrambled eggs too long, or at too high a temperature, and they will dry out. Put them on the plate, and you’ll see their poor, oversqueezed proteins continue to wring water out, leaving a puddle behind. Instead, to get the silkiest scrambled eggs, follow Alice B. Toklas’s advice and cook them over very low heat. I imagine she learned a thing or two about good cooking from her adopted hometown—Paris—where she was a member of the twentieth-century avant-garde. Crack 4 eggs into a bowl and season them with salt and a few drops of lemon juice, whisking thoroughly to break them up. Gently melt a little butter in a saucepan over the lowest possible heat and pour in the eggs. Continue to stir with a whisk or a fork, while adding 4 or more tablespoons of butter in thumb-size pieces, letting each be absorbed before you add the next. Never stop stirring, and be patient. It’ll take several minutes for the eggs to start to come together. When they do, pull them from the stove in anticipation of the cooking that will continue due to residual heat. Serve with—what else?—buttered toast.

  A little salt can help keep proteins from drying out. Recall the many advantages of salting meat in advance. One of its luckiest consequences is that, given enough time, salt will tinker with the structure of meat proteins, reducing their capacity to expel water. Consequently, meat that has been salted early will be indescribably moist when cooked properly, and even forgive being slightly overcooked.

  The coiled threads in each type of protein are unique, so the range at which different proteins coagulate is vast. Preserve tender cuts of meat with careful, quick cooking, generally over the intense h
eat of a grill, preheated frying pan, or hot oven. If cooked to an internal temperature beyond 140°F, the proteins within tender red meats will coagulate entirely, expelling water and yielding tough, chewy, overcooked steaks and lamb chops. Chicken and turkey breasts, on the other hand, don’t dry out until temperatures surpass 160°F.

  Tougher cuts, rich in sinewy connective tissue, require a slightly more nuanced cooking approach to reveal their tenderness: the investment of gentle heat, time, and water implicit in braising or stewing. Heat metamorphizes collagen, the main structural protein found in animal connective tissue, into gelatin. The tough and chewy proteins that make undercooked short ribs impossible to chew and unpleasant to eat will transform into gelatin with water, time, and further cooking, yielding the rich, tender textures we associate with barbecued brisket, stewed meats, and properly cooked short ribs. And since acid will further amplify collagen’s transformation into gelatin, add an acidic ingredient into the marinade, dry rub, or braise to encourage the process.

  The key to this transformation is gentle heat. In contrast to the carefully applied quick heat required to cook tender cuts, time and sustained low heat are essential to transforming dark meat’s tough, sinewy connective tissue into luxurious gelatin while its lumps of intermuscular fat render and baste the meat from within.