Salt, Fat, Acid, Heat. Samin Nosrat
Delicate foods especially suffer in these instances. Cooking in fat that’s insufficiently hot will cause food to absorb the oil, resulting, for example, in unappetisingly beige, greasy fish fillets, cooked through but not golden. Steaks and pork chops placed in cold fat will take so long to sear that by the time they appear to be perfectly cooked, the meat within will be well-done, rather than medium-rare.
This doesn’t mean you should categorically crank the heat. If the fat is too hot, the outer surface of the food will brown and become crisp before the centre has a chance to cook through. Crisp onion rings with crunchy slivers of onion that slip out on first bite and chicken breast with burnt skin and a raw, flabby centre both suffer from having been cooked at temperatures that were too high.
The goal with all cooking is to achieve your desired result on the outside and inside of an ingredient at the same time. In this case, it’s a crisp surface and a tender centre. Add foods that take time to cook through, such as aubergine slices or chicken thighs, to hot fat, allowing a crust to form. Then, reduce the heat to prevent burning and allow them to cook all the way through. I’ll explain more about how to navigate between different levels of heat in Using Heat.
Once you have achieved crispness, do your best to retain it: do not cover or pile up crisp foods while they are still hot. They will continue to release steam. The lid will entrap steam, which will condense and drip back onto the food, making it soggy. Allow hot, crisp foods to cool off in a single layer to prevent this from happening. If you want to keep crisp foods such as fried chicken warm, set them in a warm spot in the kitchen, such as the back of the stove, until ready to serve. Alternatively, cool the chicken on a baking rack and then pop it into a hot oven for a few minutes to reheat it before serving.
Creamy
One of the great alchemical wonders of the kitchen, an emulsion happens when two liquids that normally don’t like to mix together or dissolve give up and join together. In the kitchen, an emulsion is like a temporary peace treaty between fat and water. The result is tiny droplets of one liquid dispersed in another, resulting in a creamy mixture that’s neither one nor the other. Butter, ice cream, mayonnaise, and even chocolate—if it’s creamy and rich, chances are it’s an emulsion.
Consider a vinaigrette: oil and vinegar. Pour the two liquids together and the oil, being less dense, will float above the vinegar. But whisk the two liquids together—breaking them up into billions of tiny droplets of water and oil—and the vinegar will disperse into the oil, creating a homogenous liquid with a new, thicker consistency. This is an emulsion.
Yet little more than momentary bewilderment will hold together this simple vinaigrette. Left alone for a few minutes, the oil and vinegar will begin to separate, or break. Use this broken vinaigrette to dress lettuce and the oil and vinegar will unevenly coat leaves, tasting too sour in one bite and too oily in the next. In comparison, a well-emulsified vinaigrette will offer balanced flavour in each bite.
When an emulsion breaks, the fat and water molecules begin to coalesce back into their own troops. In order make an emulsion more stable, use an emulsifier to coat the oil and allow it to exist contentedly among the vinegar droplets. An emulsifier is like a third link in the chain, a mediator attracting and uniting two formerly hostile parties. Mustard often plays the role of emulsifier in a vinaigrette, while in a mayonnaise, the egg yolk itself has some emulsifying qualities.
Using Emulsions
Emulsions are efficient tools for enriching plain foods: a knob of butter swirled into a pan of pasta at the last moment, a spoonful of mayonnaise added into a dry, crumbly egg salad, a creamy vinaigrette drizzled over otherwise unadorned cucumbers and tomatoes for a simple summer salad.
Some cooking requires you to make an emulsion. Other times you will be handed an existing emulsion and your only job will be to keep it from breaking. Become familiar with common kitchen emulsions so you can protect their delicate bonds of cooperation.
Some familiar emulsions:
• Mayonnaise and hollandaise
• Vinaigrettes (though some are very temporary)
• Butter, cream, and milk
• Peanut butter and tahini (once you stir in the oil)
• Chocolate
• The ephemeral crema on top of an espresso
Achieving Creaminess: Mayonnaise
Mayonnaise is an oil-in-water emulsion made by slowly whisking tiny droplets of oil into an egg yolk, which itself is a natural emulsion of fat and water. Fortunately, the yolk offers us a little insurance, as it contains lecithin, an emulsifier with one end that likes fat and another that likes water. With vigorous whisking, lecithin connects the minuscule amount of water innate to a yolk to the oil droplets and surrounds tiny air bubbles. The two distinct ingredients integrate into a rich, unified sauce.
But mayonnaise—and this is true of all emulsions—is always looking for an excuse to break, or separate into the hostile groups of oil and water once again.
For a basic mayonnaise, measure out—or at least eyeball—the oil before you start. Choose your oil depending on how you intend to use the mayo—for spreading on a BLT or a Vietnamese bánh mì sandwich, use a neutral oil such as grapeseed or canola. For aïoli to serve alongside Tuna Confit in a Niçoise salad, use olive oil. Each egg yolk will comfortably hold about three-quarters of a cup of oil in a stable emulsion. Since homemade mayonnaise is best when it’s fresh, aim to make the smallest amount possible at a time, though any leftovers will keep in the fridge for a few days.
Oil-in-water emulsions always work better when their ingredients are neither too hot nor too cold. If you’re starting with an egg straight from the fridge, bring it up to room temperature before you start. If you’re in a hurry, submerge the egg in a bowl of warm tap water for a few minutes to speed things up.
Lightly dampen a kitchen towel and lay it into a small saucepan, then set the mayonnaise-making bowl in it. The wet towel will create enough friction to keep the bowl steady and prevent spillage. Place the yolk(s) in the bowl and start whisking, adding in the oil one drop at a time using a ladle or a spoon. Once you’ve added half the total volume of oil and created a relatively stable base, start to add the rest of the oil in more swiftly. If the mayonnaise grows so thick it’s hard to whisk, add a few drops of water or lemon juice to thin it out and prevent it from breaking. Once you’ve added all the oil, turn your attention to seasoning the mayonnaise to taste.
Follow these rules, and you’ll see that mayonnaise is difficult (but not impossible) to ruin. During one of his cooking lessons with me, Michael Pollan asked me to explain the science at work in an emulsion. I didn’t really know, so I responded, “Magic keeps it together.” Even now that I understand the science, I still believe there’s some magic at work.
Retaining Creaminess: Butter
One of my favourite poets, Seamus Heaney, once described butter as “coagulated sunlight,” which might be the most elegant and economical way to describe its special al chemy. To begin with, it’s the only animal fat made without killing an animal. Cows, goats, and sheep eat grass, a product of sunlight and photosynthesis, and deliver us milk. We skim the richest cream off the top, and churn it until it transforms into butter. The process is so straightforward that kids can make butter by shaking a glass jar filled with chilled cream.
Remember that butter, unlike oil, isn’t pure fat. It’s fat, water, and milk solids all held together in a state of emulsion. While most emulsions are stable in a narrow range of temperatures (just a few degrees), butter retains its solid form from