On what? A few things, but the most important factor is the type of dish you’re cooking.
How to check your oven’s temperature, and what to do if it runs hot or cold
As one guest in our weekly cooking chat stated: “I’ve been baking a lot of bread this winter, and I’ve found that I MUST preheat the oven to 350 or 375 before I put the loaves in. If I don’t, the loaves overinflate and then collapse.”
With baked goods in particular, the initial blast of high heat is important to set the outside of the structure so they hold their shape and is critical in achieving the desired texture. High heat quickly transforms the fat in pie crusts into steam to create the flaky layers that are a highlight of a great pie, causes the edges of cookie dough to set so they don’t spread too much and is a crucial part of anything that needs to rise.
“Temperature is part of the chemical reaction process for baked goods made with a leavening agent, such as baking powder,” nutrition and wellness educator Jenna Smith writes for the University of Illinois Urbana-Champaign extension website. “When baking powder is mixed in a batter or dough, carbon dioxide bubbles are produced, and unless you get it in a preheated oven quickly, the product won’t rise as it should. Yeast breads prefer a preheated oven, as well, which allows for a final ‘proofing’ or rising. Putting it into a cold oven could make the bread dense, dry and crumbly.”
Similarly, anything egg-based where fluffiness is key, such as souffles or frittatas, will benefit from going directly into an oven that’s already hot.
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For anything wet or saucy (such as a pot roast or macaroni and cheese), items for which an initial blast of heat isn’t important (such as bacon or baked potatoes), dishes that cook for a long time, and left overs to be reheated, there is no need to preheat your oven. Sure, the timing might be different if you’re trying to follow a recipe, but you should use other clues to determine doneness, such as noting how it looks or using an instant-read thermometer to take its temperature. And for some tasks, such as toasting nuts, you actually get better results when you start them in a cold oven as the gradual increase in temperature leads to a more even roast.
When it comes to roasting vegetables and proteins on a sheet pan or in a shallow baking dish, you can go either way. While these ingredients will cook just fine starting at a lower temperature, they may not brown as much compared to starting out at a higher heat. Depending on the item, you could just keep them in the oven until they reach the desired color, but certain things, including lean proteins such as chicken breasts or pork chops, run the risk of reaching the optimal internal temperature before any browning happens. And remember: Brown food is delicious food. So you might be sacrificing flavor to save a bit of energy. If you really want to make the most of the energy expended to preheat your oven, put a sheet pan in the oven so it preheats as well. then add your vegetables to jump-start the caramelization process.
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One final consideration is how your oven preheats. Some ovens with heating elements at the top and bottom are designed to use both of them to quickly heat the cavity, and then the top element turns off once the desired temperature is reached. “In ovens that are preheated using both the top and bottom elements, food is put in before the preheat cycle was up burned on top,” Cook’s Illustrated found.
So in most instances, your food is usually better off going in a preheated oven. In fact, it is a must for basically anything with flour or eggs (or their proxies for gluten-free or vegan baked goods). And if time is your main gripe when it comes to preheating, here’s a trick food writer Becky Krystal shared: “Start preheating using the broiler to get a higher temperature faster before switching to bake.”