Salt, Fat, Acid, Heat

by Samin Nosrat

  Use this chemistry to your advantage when deciding how to cook vegetables. Boiling dilutes the relatively acidic liquid contained in vegetable cells, so it will generally yield more tender vegetables than roasting will. Roast big, beautiful slices of cauliflower or Romanesco broccoli to ensure they retain their shape. Boil potatoes or parsnips so that they melt into a puddle of tenderness, perfect for puréeing or mashing.

  Acid also encourages bonds between pectin groups—the gelling agent in fruit—so that they can trap water to help set jam or jelly. Some fruits, such as apples and blueberries, don’t contain enough acid to bond the pectin on their own, so we help them along by squeezing some fresh lemon juice into the jam pot and into fruit fillings for pies and cobblers to encourage them to set.

  Acid is required when using chemical leavenings such as baking soda or baking powder. Visualize the baking soda and vinegar volcanoes of your elementary school science projects. Just like that, but on a much smaller scale, acid reacts with baking soda to release carbon dioxide bubbles to leaven baked goods. Doughs and batters leavened by baking soda should also have an acidic ingredient such as natural cocoa powder, brown sugar, honey, or buttermilk. Baking powder, on the other hand, already contains powdered tartaric acid and doesn’t need an external source of acid to react.

  Acid encourages the proteins in an egg white to assemble, or coagulate, more quickly but less densely than they otherwise would. Under normal conditions, strands of egg proteins unravel and tighten when heated. As they do, the strands squeeze out water, causing eggs to toughen and dry out. Acid draws egg proteins together before they can unravel, which inhibits them from joining too closely. A few secret drops of lemon juice will produce creamier, more tender scrambled eggs. For perfect poached eggs, add a capful of vinegar into boiling water to help speed up coagulation of the white and strengthen the outer texture, while preserving the runny yolk.

  Acid aids in stabilizing whipped egg whites by encouraging more, finer air pockets, helping to increase the volume of the egg white foam. Though cream of tartar—a by-product of wine-making—is the form of acid traditionally added to egg whites as they’re whipped for meringues, cakes, and soufflés, a few drops of vinegar or lemon juice per egg white will yield a similar result.

  Dairy proteins called casein will coagulate, or curdle, with the addition of acid. With the exception of butter and heavy cream, which are very low in protein, dairy should only be added to acidic dishes at the last minute. While curdled fresh dairy, when unintended, is usually inedible, this same reaction makes cultured dairy—from yogurt to crème fraîche to cheese—possible, offering us a delicious, entirely new category of acidic ingredients to incorporate into food. Try making your own crème fraîche—it couldn’t be easier. Just combine 2 tablespoons of crème fraîche or cultured buttermilk with 2 cups of heavy cream. Pour into a clean glass jar, cover loosely or leave uncovered, and leave out at warm room temperature for 2 days, or until it thickens. That’s it. Use it in Blue Cheese Dressing, Chicken with Vinegar, or Tangy Whipped Cream. Cover and store it in the fridge for up to two weeks. Use the last few spoonfuls to start the next batch in the same way.

  When acid is incorporated into doughs and batters, it will tenderize them, much as fat does. Whether it comes in the form of cultured dairy, natural (nonalkalized) cocoa powder, or vinegar, acid in a dough or a batter will disrupt the gluten network, resulting in a more tender product. If it’s chewiness you’re after, wait as long as possible into the process of dough-making to add acidic ingredients.

  Acid tenderizes, then toughens, meat and fish proteins. Imagine protein as coiled strands folded up into bundles. When acid comes into contact with the coils, they unfold and unwind. This process is called denaturation. These denatured proteins then begin to bump into each other and coagulate, reconnecting into an intimate network. The same thing happens when proteins are heated, which is why acid is sometimes said to cook meat or fish.

  At first, the intimate network traps water that was previously bound up in muscle fibers, leading to moist, tender food. But if the denaturation conditions persist—that is, if food continues to sit in acid—the protein network will continue to tighten, squeezing water out of the protein altogether, resulting in tough, dry food, much like an overcooked steak.

  To understand this progression, consider the way the texture of a piece of sashimi will become tender, bright-tasting fish tartare with the addition of acid, and then turn into a chewy ceviche over time. Fish meant for cooking shouldn’t marinate in acid for more than a few minutes, but dip any flaky, white-fleshed fish into buttermilk and flour before frying, or toss sea bass with lemon juice and curry powder just before skewering and grilling, and you’ll get the benefit of moist texture along with the pleasant hit of tartness.

  Acid also helps break down collagen, the main structural protein found in tough cuts of meat. Add wine or tomatoes as you begin to cook braises and stews, since the more quickly the collagen melts, the sooner the meat will grow juicy and succulent.

  Producing Acid

  While we introduce salt and fat into our food in the form of distinct ingredients, there are two easy ways to produce acid in food as we cook. One process is rather fast, the other rather slow.

  The fast method? Browning foods. In Salt and Fat, I explained that food begins to brown once its surface temperature climbs considerably beyond the boiling point. This can happen in the toaster to a slice of bread, in the oven to cookies and cake, on the grill to meats, fish and vegetables, or in the pan to caramel. The chemical reaction involved in browning sugars is called caramelization. The chemical reaction involved in browning meats, seafood, vegetables, baked goods, or just about anything else is called the Maillard reaction, after Louis-Camille Maillard, the scientist who discovered it. There will be more details about these delicious, mysterious chemical reactions in Heat.

  Though they’re entirely different processes, caramelization and the Maillard reaction share some similarities. Both create acidic flavor compounds, in addition to many other tasty molecules, as by-products. As it caramelizes, a single sugar molecule will develop into hundreds of new and different compounds, including some acids. In other words, equal amounts of sugar and burnt caramel by weight are not equally sweet, and in fact caramel is acidic! Similar acidic compounds are produced in carbohydrates and proteins by the Maillard reaction.

  Though producing acidity is rarely a reason to brown food, knowing that the process will develop a host of new flavors, including some sour ones, can be a valuable tool. Imagine tasting two batches of ice cream, both made with the same amount of sugar. In one batch, the sugar was added directly to the dairy. In the other batch, some of the sugar was cooked into dark caramel before being mixed in. The ice cream made with caramelized sugar will not only taste less sweet but will also be far more complex, because it has the vital flavor contrasts that acid provides.

  The other, much slower, method for producing acid in the kitchen is fermentation, where, in addition to many other flavor-producing processes, carbohydrates transform into carbon dioxide and acids or alcohols using yeasts, bacteria, or a combination thereof. Wine, beer, and cider are of course fermented, but so are naturally leavened breads, all sorts of pickles, cured meats, cultured dairy, and even coffee and chocolate.

  Some of the most delicious bread I’ve tasted is naturally leavened, and has been allowed to rise—which is to say ferment—slowly. According to Chad Robertson, of Tartine Bakery in San Francisco, who lets his dough rise for more than thirty hours, slow fermentation “improves the flavor, in large part because more sugars are available to caramelize during the baking. The loaves brown faster and the crust gets darker.” Subtly sour, Chad’s bread is layered with complex flavors; every time I taste it, I enthusiastically declare it the best loaf of bread in the world! Bake a naturally leavened loaf of bread sometime when your schedule allows. The results can be stellar, especially if you bake it Chad’s way and let the elements in the crust undergo both caramelizati
on and the Maillard reaction, yielding layer upon layer of acidity and sweetness.

  USING ACID

  As with all good cooking, the best way to use acid well is to taste, over and over again. Using acid is much like using salt: if something is noticeably sour, it’s probably got too much acid. But if a food tastes bright and clean, then its acid balance is spot-on.

  Layering Acid

  When considering acid, think about which acid or combination of acids to use, and when to add them. Just as with salt, and fat, a single dish can often benefit from several forms of acid: think of this as layering acids as you cook.

  Cooking Acids

  Learn to use acid like salt to season food from within. While acid presents many last-second opportunities to adjust dishes—with a final squeeze of lemon, crumble of goat cheese, or pile of pickles—some acids should be worked into dishes from the start. These are what I call cooking acids. Examples include tomatoes in pasta sauce, white wine in Poultry Ragù, beer in a pot of chili, vinegar in Chicken with Vinegar, and mirin (rice wine) in Glazed Five-Spice Chicken.

  Cooking acids tend to be mellow, transforming the foods with which they are cooked slowly, over time. They can be extraordinarily subtle; while their presence may go undetected, their absence is sharply felt. I learned this painful lesson when at the request of a distant relative, I tried to make beef bourguignon without the Bourgogne in Iran, where wine isn’t readily available. No matter what I did, I couldn’t get the dish to taste right without that crucial ingredient.

  Give acid the time it needs to do its silent work when macerating shallots and onions. Macerate, from Latin, “to soften,” refers to the process whereby ingredients soak in some form of acid—usually vinegar or citrus juice—to soften their harshness. Simply coat the shallots or onions in acid—they don’t need to be completely submerged. If you plan on using a couple of tablespoons of vinegar for a dressing, just coat the shallots with it first, and wait 15 or 20 minutes before adding oil to build the dressing in the same cup or bowl. It will be enough to prevent dragon breath.

  There’s no replacement for working acid early into braises and stews; the remarkable alchemy of time and heat will soften any dish’s sharp edges. Omit the tomatoes and beer from Pork Braised with Chilies and the sweetness of the aromatic base of onions and garlic will dominate. The sweetness resulting from browning needs the foil of acid, too. Deglazing a pan with wine, whether for risotto, pork chops, fish filets, or a more complex reduction sauce will keep a dish from skewing too sweet.

  Garnishing Acids

  Garnishing acids, on the other hand, are used to finish a dish. While no amount of salt at the table will make up for underseasoning food from within, a hit of acid at the very last second often improves food, which is why garnishing acids are so important. As the volatile aromatic molecules disperse over time, the flavor of fresh citrus juice will transform, losing some of its brightness—so freshly squeezed juice is best. The application of heat will change the flavors of both citrus juice and vinegar, dulling the former and mellowing the latter, so add them just before serving when you want their full flavor impact.

  You can incorporate different garnishing acids into a single dish to increase flavor. Balsamic vinegar isn’t always acidic enough to dress a salad on its own, so spike it with red wine vinegar. Or layer vinegar with citrus juice, which is brighter: make Citrus Vinaigrette with white wine vinegar and blood orange juice to drizzle over an Avocado Salad. The strong acidity of the vinegar will balance the richness of the avocado, while the vivid orange juice will round out its flavor.

  When you can, use the same kind of acid for cooking and garnishing—spoon tomato salsa, for example, atop pork braised with tomatoes; finish a risotto with a fresh splash of wine from the same bottle used earlier to deglaze the pan. This kind of layering offers multiple tastes of the same ingredient.

  And then there are times when a single form of acid isn’t enough to accomplish its task. Feta cheese, tomato, olives, and red wine vinegar offer four distinct forms of acid in a Greek salad. To bring out a chorus of bright, happy notes, serve that pork I mentioned above with all kinds of acidic condiments, including queso fresco, sour cream, and a Bright Cabbage Slaw tossed with vinegar and lime juice.

  And think back to that Caesar salad, where Parmesan and Worcestershire sauce—sources of acid—both lend the dressing tang as well as salt and umami. Balance the creamy, salty dressing with wine vinegar and lemon juice. Tinker with all four sources of acid as you taste and adjust, little by little, until it’s perfect.

  Make Pasta alle Vongole to practice layering acids. I like to make clam pasta with two varieties of clams—littlenecks, which lend an intense brininess to the dish, and cherrystones or Manilas, which are small enough to toss in whole and eat directly out of the shell along with the pasta. First, set a pot of water to boil and season it with salt. Rinse the clams and dice an onion, saving the root ends. Heat a large frying pan over medium heat and splash in some olive oil. Add the root ends of the onion, a few parsley sprigs, and as many littlenecks as will fit in a single layer, then pour in enough wine to cover the bottom of the pan. Turn the heat up and cover the pan. Let the clams steam until they open, which should take two or three minutes. Use tongs to pull the clams from the pan into a bowl as they open. Some of the stragglers might need a little encouragement, so tap them with your tongs if they’re taking too long.

  Cook the rest of the littlenecks in this way, adding more wine if needed to cover the bottom of the pan. When you’ve removed all of the clams from the pan, strain the liquid through a fine-mesh strainer or cheesecloth; this clam-cooking liquid is priceless. Plus, it’s now the dish’s main source of acid. When the clams are cool enough to handle, pluck them from their shells and run a knife through them, then return them to the clam-cooking liquid.

  Rinse out the frying pan, then set it over medium heat. Add just enough oil to coat the pan, and when it shimmers, add the diced onion and a pinch of salt. Stirring from time to time, cook the onion until it’s tender. It’s fine if it picks up a little color, but don’t let it burn; add a splash of water if you need to. Then taste the pasta water, make sure it’s as salty as the sea, and cook the linguine until it’s not quite al dente, about 6 or 7 minutes.

  Add a clove or two of sliced garlic and some red pepper flakes to the onion and allow it to bloom, or sizzle gently without taking on any color, then add the cherrystones or Manilas and crank up the heat to high. Add a healthy splash of the clam-cooking liquid and cover the pan. As soon as the little clams pop open, use a slotted spoon to add the chopped littlenecks into the pan. Cook all of the clams together for about a minute, and then taste and adjust the acid with more white wine or a squeeze of fresh lemon juice.

  When the pasta is not yet al dente, drain it, reserving a cup of the pasta water. Add the noodles directly to the pan with the clams. Continue to cook the pasta, swirling the pan, until the noodles are cooked al dente. This way, the pasta will absorb all the briny flavor of the clam liquid as it finishes cooking. Taste again and adjust for salt, acid, and spiciness. If the noodles seem dry, add some of the reserved pasta water.

  Now begins the magic of garnishing (and fat). Intensify the creaminess and flavor of the dish by tossing in a knob of butter. Next, add chopped parsley and some freshly grated Parmesan. Some might balk at adding cheese to a seafood pasta, but I learned this trick from the chef at a beloved seafood restaurant in Tuscany, where this pasta was so delicious it helped me overcome my lifelong aversion to clams. The salt, fat, acid, and umami offered by the cheese makes this pasta unforgettable. For a final touch of acid and crunch, sprinkle the dish with toasted sourdough bread crumbs. They’ll be crisp when you first dig in, but as they mingle with the pasta, the bread crumbs will absorb the clam juice, becoming little flavor bombs exploding with each bite.

  Condiments and Umami

  Cervantes may have thought that “hunger is the best sauce,” but I’d argue that sauce is the best sauce—because s
auce can complete a dish. Sauce, and in fact most condiments, are sources of both acid and salt, they offer a pretty surefire way to improve flavor. The bonus is that they are often excellent sources of umami, which is the word, from Japanese, for the fifth taste we can sense, the other four being sweet, sour, salty, and bitter. The closest translation into English is something like “deliciousness,” or “savoriness.”

  Umami is, in fact, the result of flavor compounds called glutamates. The most familiar glutamate is monosodium glutamate, or MSG, the white powder often generously used in the kitchens of Chinese restaurants to enhance flavor. Though MSG is chemically manufactured, there are also many natural sources of glutamates. Two foods most abundant in naturally occurring glutamates are Parmesan and tomato ketchup. Sometimes a grating of Parmesan can make the difference between a good bowl of pasta and a great one (even Pasta alle Vongole). And then, there are those of us who always crave ketchup with our burgers and fries, and not only because of the sweetness, salt, and acid that it provides. A little ketchup—and the umami it offers—makes things taste inexplicably more delicious.

  Since the list of foods rich in umami dovetails nicely with many sources of salt and acid, always seek the opportunity to work in a little umami along with salt or acid to heighten flavor without having to do any extra work.