One of the most important “chemistry-lite” lessons for home cooks relates to the how’s and why’s of browning food. In most cooking, browning takes one of two forms: caramelization, and the “Maillard reaction.” Caramelization is the browning of sugars; the Maillard reaction is the browning of proteins. Both have similar results: the production of a set of chemicals that add a ton of flavor to our food – flavors that we crave. The change in color itself is pretty insignificant, other than it signals that the chemical reaction we were looking for has happened (and of course it makes our food look yummier because we’ve come to associate browned food with certain very desirable flavors).
The shorthand for the Maillard reaction is, “Protein browns at 350 degrees.” That is, of course, an oversimplification; the Maillard reaction slowly starts to kick in when food is around 300 degrees, and it’s going full speed by the time it reaches 350. But the important principle to take away from this is that there is a threshold at about 350, above or below which your food cooks very differently. You could cook it all day at 250 degrees, and it will never brown (but it will still dry out, because that’s above the temperature at which water boils – heat your food to 250 degrees and all its water will start disappearing as steam).
This is why so many recipes call for baking at 350 degrees: it’s the lowest temperature where you are assured to get browning, but it will happen slowly enough that you can decide when your food is brown enough and remove it from the oven. It’s also why some long-cooking recipes, such as roasted poultry, tell you to bake at 325 degrees until the internal temperature of the roast is almost high enough, then crank it up to 375 or 400 for the final 15 minutes to brown the exterior. Or the reverse: some recipes call for 15 minutes at high heat first, supposedly to trap in the moisture by browning the exterior, then turn down the temperature to 325 to stop the browning but let the internal temperature continue to rise.
There are other important lessons to be learned from knowing about the Maillard reaction. One is to always dry your meat before you cook it. If you put wet meat in the oven, then the outside won’t brown until all the water has evaporated off – but the inside will still be cooking.
The Maillard reaction applies outside the oven, too. Boiled food will never brown – it will never get above 212 degrees. Deep-fried food will brown, if you heat the oil above 325 or so (and make sure you are using an oil that has a smoke-point well above 350!); but if your oil isn’t hot enough then its color means nothing: your food could be thoroughly cooked but not at all browned.
Open flames can get much hotter than 350 degrees, as can a frying pan or wok on a kitchen burner. That’s why food browns (and burns) so quickly sometimes when cooking on a stovetop.
Caramelization is a similar process, though the temperate range tends to be a bit higher than for the Maillard reaction: depending on the type of sugar, from 320 to 360 degrees. The acidity of the food can affect how quickly sugar caramelizes: more acidic or alkaline foods will caramelize faster, while those in the middle will do so slower.
Understanding the Maillard reaction and caramelization is a very important and powerful tool for cooks; it helps us understand what is going on in a recipe. If it calls for baking at 300 degrees, we know it’s trying to cook it through without browning it (and that we don’t have to pay close attention to it while it’s cooking). If we’re baking at 350, we’re trying to slowly brown it. And if the temperature is higher, we know that we’re trying to cook it fast – and that we have to watch it carefully to make sure it doesn’t overcook.
This also sheds new light on the ubiquitous slow-cookers, which specialize in “low and slow.” The main point of cooking most food is to raise the internal temperature high enough and for long enough to kill off any bacteria or other evil things that might get us sick if we consume them. And you can do that by cooking at high, medium or low temperatures; the difference is in whether the outside and inside get cooked the same amount, and whether any browning happens along the way. Cooking can also soften or “tenderize” food so that it’s easier to eat and digest, but again that’s mostly a matter of the temperature you raise the food to, how long you keep it at that temperature, and any other chemical reactions that happen along the way (like browning). You can cook a chicken breast in your oven at 350 degrees for 20-25 minutes (depending on how thick it is), or in a slow-cooker for an hour. It will be safe to eat either way, but your decisions about how to cook it – armed with an understanding of how browning works – will affect how it comes out in the end.