The word sauté (pronounced "saw-TAY") refers to a form of dry-heat cooking that uses a very hot pan and a small amount of fat to cook the food very quickly. Like other dry-heat cooking methods, sautéeing browns the food's surface as it cooks and develops complex flavors and aromas.
When sautéeing, it's important to get the pan very hot, then add the fat (butter or oil) and let it get hot as well, before adding the food to the pan.
This hot fat helps coat the food so that the surface will brown evenly.
Another key is to avoid overloading or overcrowding the pan. In order to achieve the desired browning of the food, the pan needs to stay hot throughout the cooking process. Too much food in the pan dissipates the heat, causing the food to steam or boil rather than sauté.
Finally, when you sauté, you want to keep the food moving. The word sauté actually means "jump" in French. Tossing or flipping the food in the pan ensures that it cooks evenly, but it also helps keep the pan hot.
The reason it's important to keep the food moving around is that when a hot thing meets a cooler thing, their temperatures eventually meet in the middle. The cooler thing grows warmer while the hot thing cools down.
How Sautéeing Works
To illustrate, imagine a pan with green beans cooking in it. The beans at the bottom of the pan, closest to the heat source, are nice and hot, while the ones on top, where they're exposed to air, are cooler.
And the longer they sit like this, the greater this disparity in temperature becomes.
So far, so good. However, you're eventually going to want to cook the beans on top, too. And once you flip them, the ones from the top come into contact with the pan's surface and, because they're cooler, they actually lower the temperature of the pan.
This leads to the same problem mentioned earlier, where the food ends up steaming rather than sautéeing. That's why we try to keep everything moving more or less constantly.
To facilitate this, some sauté pans have sloped sides, which makes it easier to flip those items in the pan without flipping them all over the kitchen. However, it's worth noting that this flipping or tossing technique is only really practical with smaller pieces of food, especially vegetables.
So for steaks, larger cuts of poultry, fish fillets and so on, we're more likely to employ a technique known as pan-frying rather than sautéeing — even if the dish is actually called sautéed fillet of sole or whatever. For a demonstration, here's a video on how to sauté vegetables.
By the way, when you sauté at home, you don't actually have to toss the food around in the pan. If you've never done it before, you don't want to end up with food all over the floor, or your kids or your pets. It's fine to use a wooden spoon or heatproof spatula to move the food around.
But if you want to practice your tossing, use a cool pan with some dry beans in it.
Pan-Frying Vs. Sautéeing
What's pan-frying? It's a lot like sautéeing, but with a few key differences. Besides the fact that there's no tossing, pan-frying uses slightly more fat and slightly lower temperatures than sautéeing. This makes it a good method for cooking larger pieces of meat that would not have time to cook through because with sautéeing, the food isn't in the pan for very long.
For that reason, larger pieces of meat are often finished in the oven after the surface has been cooked to the desired degree.
Also see: How to Stir Fry