If you thought fats only came from slabs of meat (or that persistent pouch around your middle), then it's time for us to have a talk. First off, fats are all over the place, and that's not a bad thing: when it comes to cooking, fats are an essential tool in your arsenal. They're also a much broader category than you may have realized—cooking fats span a wide array of triglycerides, from run-of-the-mill canola and fancy just-for-drizzling olive oil to, yes, those tubs of lard and sticks of creamy, delicious butter.
But getting to know your fats can be a slippery business. If wading through the myriad bottles on supermarket shelves wasn't already a daunting task, then the latest word on saturated fats is enough to turn everything on its head. In this series, we'll be talking about what makes fats special, how to tell them apart, and how to pick the best one for the job.
Now, if you're anything like me, you've probably spent most of your life thinking of fats in terms of their source—animal fats versus seed- and nut-based vegetable oils—with perhaps a vague awareness of terms like "refined," "smoke point," "saturated," and so on. There are a lot of ways to categorize fats, but without a handle on what they actually do, chances are that none of that information is actually going to stick.
So how do fats and oils work and what sets them apart from other cooking liquids?
1. Fats are hydrophobic
In other words, fats repel water like a stinky teenage boy repels...everyone. This is probably a familiar concept if you've ever tried to make a basic vinaigrette—mix up some oil and vinegar (the latter, a water-based acid), and they'll insistently separate into two distinct layers in a matter of minutes. Even oil-based emulsions like mayonnaise rely on a third party to hold each tiny droplet of oil in suspension—egg yolk, mustard, or certain starches are common choices. It may be annoying when you're trying to dress a salad, but when it comes to cooking, that stand-off between oil and water can your secret weapon.
Take deep-frying, for instance. Properly deep-fried food relies on the tension between hot oil and steaming water. Most foods you deep fry are packed with water molecules that turn into steam at high temperatures. As that steam escapes, the outer layers of food (whether it's a bare potato, a breaded chicken cutlet, or a battered onion ring) dry out, some of that water getting replaced by more flavorful fat*. Meanwhile, proteins coagulate and brown, creating the crisp, golden crust that's the hallmark of perfectly fried food. Check out our guide to deep frying for more info!
*despite what some folks tell you, food fried at higher temperatures actually absorb more oil than those fried at cooler temperatures
2. Fats conduct heat, and can do so at higher temperatures than water
Even a thin layer of fat conducts heat, and unlike water, it won't evaporate at high temperatures. When you baste a roast in fatty pan drippings, that coating functions as a temperature buffer, allowing your food to heat evenly and preventing the exterior from drying out before the interior is fully cooked. Now, think back to that elementary school science class on phases changes: Under normal conditions, water cannot be heated past its boiling point—212°F at sea level. Fats, on the other hand? We're talking potential temperatures of 400, even 500°F. That's hot.
And hot is exactly what you want when you're looking for a great sear or crust; it isn't until you hit temperatures above 300°F that the delicious browning known as the Maillard effect take place in earnest, and the higher the temperature, the faster those reactions occur
3. Fats lubricate food
Ever wonder why recipes tell you to preheat your sauté oil? When you throw a raw steak onto a dry, searing-hot pan, all its surface proteins reach out their tiny protein arms and grab hold, forming covalent bonds with the metal surface. Add some nice, hot fat to the mix and that heat will change their shape; the proteins lose their ability to, erm, cling. We've got the full explanation here, but here's the moral of the story: fat in your pan = sticking averted.
4. Fats affect flavor
We all know that fat affects flavor thanks to the mouth-coating richness that butter or olive oil can impart to a dish. But fats do more than add textural nuance. Many of the flavor compounds that make herbs and aromatics such compelling seasonings are what we call fat-soluble, meaning they'll actually spread and coat your tongue better when they're immersed in lipids. Using fat in anything from marinades to braises helps coax out, layer, and evenly distribute flavors.
Of course, some fats do more than just distribute flavor—they provide it. "Pure," unrefined or minimally refined oils like extra-virgin olive, sesame, coconut, and hazelnut oils, for example, have easily recognizable flavors; others, like canola or peanut oils, are neutral. Depending on what you're making and how you're making it, flavored oils can be your best friend or your worst enemy.
Next in this series: the smoke point. What is it and why does it matter? Read all about it here.