For every person who has ever forgotten to preheat their oven, there are probably at least a few who simply choose not to. But does it even matter?
The answer depends on what you’re making. A preheated oven is pretty essential for anything that contains a leavening agent like yeast (think bread), baking powder (cakes, cookies, and other baked goods), or eggs (e.g. soufflés and meringues). In short, if your dish needs to rise, you shouldn’t skip preheating your oven.
“It’s the culinary equivalent of hitting the ground running,” chef Rosie Sykes told The Guardian. “Some dishes, such as breads and cakes, require an immediate blast of heat, either to push them into action or to make them set as fast as possible.” If you slide your dish into a cold oven so they can slowly heat up together, you risk sabotaging the delicate chemical reaction that allows air bubbles to expand at the optimal speed. The end result could be a collapsed soufflé or a dry, crumbly loaf of bread.
Roasted vegetables, roasted meats, and basically anything else you want to get nice and brown on the outside will also turn out better if you preheat your oven; that way, the chemical process that causes food to brown can start immediately. Otherwise, the inside of whatever you’re making might be way overcooked by the time the outside crisps up.
According to Bon Appétit, preheating is nonessential for “dishes with a lot of moisture”—like casseroles—or slow-bake recipes like braises, which are much less dependent on finicky chemical reactions in order to look (and taste) good.
All that said, the best way to maximize your dish’s chances of being as delicious as the recipe claims it’ll be is to just follow the recipe.
“If your oven isn’t at the prescribed temperature when the pan goes in, there’s no guarantee that you’ll get what the recipe developer created or what you want,” cookbook author Dorie Greenspan told Snopes. “When the recipe’s instructions say preheat the oven—do it.”
Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at firstname.lastname@example.org.