Why does EVERY product that is to be cooked in a conventional oven say in the directions “1. Preheat oven to…”?
What’s the point? Why can’t I just put my food in a cold oven?? Wouldn’t most of the heat escape a preheated oven anyway because I have to OPEN THE DOOR to put the food in???
Because that’s how it’s done in the product test kitchens. [the “control”]
Or maybe you have to pre-heat your oven because you can’t trust it to do it on its own…
Different ovens heat up at different rates,so it is impossible to make a recipe without a common starting point.
Although you do loose some heat the oven retains most of its heat in the element and surfaces in the oven. Ovens cook mostly through radiative heating than convection (unless it’s a convection oven in witch cooking times are less) so a loss of hot air does not make much of a difference.
How long could it possibly take to heat up? How could that amount of time make a difference??
Let’s say you’re supposed to be baking at 350 for an hour. If you don’t preheat, it would take maybe a minute to reach 350? What difference does one minute make for something that cooks for an hour??
Well for my old piece of crap oven, to get it up to 350, your talking about at least 20 minutes, to pre heat.
Most stuff you put in the oven needs even heat, not rapidly changing heat, so you get the oven up to temp before cooking.
However, there is a frozen pizza (Freshetta or Di Giorno, or one like those) designed to be put into the oven with no preheating. The pizza is even made with slightly flattened sides so it fits easily on a cookie sheet. So it looks like the convenience food people are already hard at work trying to design around that preheat problem.
Depends on what you’re doing…
If your baking breads or pies, you absolutely need to preheat the oven so the outside can seal in the steam. If you don’t preheat the oven, your bread will not rise as much. With pies, you want the crust to crisp relatively quickly. If you don’t preheat, the filling will soak into the crust and the crust will become soggy.
When broiling, you must preheat and put the rack relatively close to the element so that the meat can sear and seal in the juices.
When roasting, you can get by without preheating but you need to add at least 5-10 minutes of extra cooking time.
** thewiz**- “*If your baking breads or pies, you absolutely need to preheat the oven so the outside can seal in the steam. *”
Seal in the steam? Breads??
Even if your cooking Wonder Bread, it will have plenty of small holes in it, regardless of whether you preheat or not. I would think the SUPERHEATED STEAM should have little problem passing through BREAD.
A MINUTE? What kind of oven do YOU have? Nuclear Fission?
It’d take a conventional oven 15-20 minutes to crank up to baking temperature.
Say you wanted to make a pizza. Your dough’s all carefully spread out, you’ve doled on the sauce and the mozzerella and the anchovies. Cookbook says “Bake 10 minutes at 475.” Okay, you turn on the oven, bung the pie in, and set the timer for ten minutes.
You take it out after the allotted time, and you’ve got raw dough and cold cheese, because now your oven’s only up to about 250.
If you make bread in an oven that is not preheated, the crust hardens too soon and prevents the loaf from rising properly - you end up with a heavier loaf.
15-20 minutes? What kind of oven do you have? Firewood? 
My oven takes roughly 4-6 minutes to get to 350F to 450F.
Perhaps, LolaBaby, your oven is already half-way there, seeing as you live in Hawaii. 
Seriously though, Ike’s oven might not be the most efficient, but I’d be really surprised to see a regular consumer oven that heated to 450F in less than 10 minutes. I’ve been an avid cook (including baking) for 20+ years, and I always have to allow at least 10 minutes for the oven to heat up to baking temperature (which is almost never as high as 400F).
With regard to the OP, the reason that recipes instruct you to pre-heat the oven is as has already been stated: achieving the target temperature will not take the same amount of time across all models of ovens, making it difficult to predict how long the food should cook. As also noted, the low temperatures can have an adverse affect on some foods (actually, it’s a common trick to bake bread at a slightly lower temperature for a little longer than usual to get a thicker crust).
The crust formation in bread is also improved a great deal by increasing the amount of water vapour in the oven; you can’t do this in a cold oven.
Very important! Do not preheat your microwave oven. Also they work best when fitted with a microwave antenna.
One other issue. In many ovens the upper element is used only for the preheating cycle. If you stick the food in too early it can get broiled at first.
and I have two bricks in the oven to keep the temperature
nice and even, even when I open the oven door. This is
of course for bread baking, where you want to bake with
falling temperature (beginning with a really high one).
That way you get a good crust.
To add to the bread debate: You can bake yeast leavened breads in a cold oven. The bread continues to rise along with the oven temperature and then bakes.
As for the steam and the initial high temperature, it depends on what you like in a crust. The steam causes a crisp crust which may or may not be what you want.
Okay, now I’m gonna have to go home and test my oven to see how long it takes to preheat. But I was thinking it tended to take around five to ten minutes. Mine’s an old (but not ancient) electric oven (is yours gas? could that make a difference?). I know some newer ovens have spiffy “fast preheat” features.
I have a brand-new midmarket Kenmore gas range, which takes about 8-10 minutes to reach 350. I learned to my chagrin that the “preheat” buzz will ring after the oven’s only about 2/3 of the way there, which plays havoc with timing. I wait until my thermometer actually reads the temp I want.
BTW, I think what The Wiz was getting at in terms of steam and bread crusts is the steam generated internally as the dough heats up. A preheated oven will form a crust more rapidly, sealing in this internal steam. But my experience is that using a preheated oven will result in a lower rise, precisely because the crust forms more quickly - it gives less time for extra rising. That can be good for the bread’s texture, depending on what effect you’re going for - it makes the bread somewhat denser.
Now, as for heat loss when you open the door - assuming you just open it, pop your food in, and close it with no fussing around, you should’t lose more than about 25 degrees F. Even with fussing, I don’t think I’ve ever lost more than 50.
I judge my oven’s preheat by watching the duty cycle light: When it’s on, the temperature is a little below the set temperature, and so the elements are on to heat it, and when it’s off, the temperature is a bit above, so the elements are turned off to let it cool a bit. At 350 F, it usually takes about 25 minutes before the light turns off for the first time. Mine is an older oven, so it may be a bit slower than a newer one, but that’s part of the problem: If all ovens preheated in 25 minutes, then many recipes would be able to take that into account, but with some taking 25 and some taking 10, you can’t make consistent recipes.