What Happens When You Don't Preheat Your Oven
There are a few reasons this is important, all which matter to your batter.
Imagine this: you whip up a cake batter according to that great cake recipe you know is going to be delicious, pour it into the prepared baking pans, and insert the pans into the oven. You turn on the oven and wait for your cake to come out beautifully light and fluffy. It doesn't.
What went wrong?
One answer is that there was something wrong with the recipe. It wasn't as great as you originally thought it would be and it failed miserably.
The other answer is that you forgot to preheat your oven. By turning the oven on after the food is in the oven, a few things happen that you don't want to happen:
1 Your food steams rather than bakes or roasts.
When you're cooking, one of the best ways of creating flavor is by searing your meats. To do this, you usually have to jack up the heat of your stove and wait for it to get ripping-hot before placing your meat in the pan. You also don't want to crowd the pan since this can lead to the food steaming rather than searing.
The idea is the same when preheating an oven. In this case, however, the oven is the stove and the pan combined. By not preheating your "stove and pan" before placing your meat in the oven, the meat will steam before it can sear at that ripping hot temperature it should be roasting in. The high heat is the reason for the wonderfully browned tops of roast chickens, pork loins, and roast beef. You rob your meat its chance of becoming extra flavorful by skipping or skimping on the heat.
2 Your dough melts before it can firm up.
This may just be the worse thing that can happen to a cookie. You place your cookie dough in the oven, expecting vanilla-scented mounds of soft chewy cookies. Instead, you're greeted by a tray of flat cookies that basically melted in the oven. What happened?
When you placed your cookie dough tray in the oven, the butter in the dough was in a moderately solid state. When the oven is at the right temperature, the butter melts at the same time as the eggs and the flour cooks, creating little mounds of cookie. When you place the dough in the oven before it's at the right temperature, the butter melts faster then the eggs and flour can firm up. That's why cookie dough is flatter if your dough isn't chilled.
3 Your batter or dough didn't rise.
Since the heat is neither constant nor hot enough to properly activate your leavening agents (baking soda, baking powder, yeast, and the eggs), your food will not rise properly. If you've ever seen misshapen dough or cakes, one problem might be that the oven had not been preheated properly. The oven was still trying to get to that temperature you set when you placed the food in so in its attempt to reach that temperature, the batter bakes unevenly. Some parts are baked but others not and results in overbaked edges with underbaked centers, sunken cakes, and tough bread that just didn't rise enough.
4 Your food takes longer to cook and may overcook.
You placed your food in the oven before it was preheated correctly but it still came out cooked through. However, you may find that not only did you food now take longer than the recipe specified, but it might have also overcooked. The longer cooking time makes up for the heat not being at the right temperature but this also means your meat cooks longer, resulting in drier meat. Your cakes, cupcakes, and other baked goods meanwhile may have golden brown tops but the centers won't be done yet. Baking these longer will mean a browner top that may crack as the heat increases, too.
Preheating your oven may seem like it's a waste of energy and gas, but the reasons behind firing up your oven before your food is placed in it can be the line between a successfully roasted chicken and a pale, tough, and dry chicken. The 20 minutes or so it takes to effectively preheat your oven to the right temperature is 20 minutes we're sure you will gladly give if it means that you don't waste ingredients trying to make something delicious.