Does it matter how long I preheat my oven?

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Does it matter how long I preheat my oven?

Postby Spot » Sat Jun 19, 2010 4:25 am UTC

So I'm cooking a pizza right now, and the instructions say, "for best results, preheat oven to 400 degrees Farenheit for 10 minutes." It specifies the actual cooking time right after that, so the only way I can think to interpret this is as an instruction to leave the oven at four-hundred degrees for ten minutes before putting in the pizza. Like, so it will cook better or something. But four-hundred degrees is four-hundred degrees, right? Is there some scientific reason why waiting the ten minutes is important or is it just to account for ovens that heat up faster than they think they do?

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Re: Does it matter how long I preheat my oven?

Postby poxic » Sat Jun 19, 2010 4:31 am UTC

Because putting it in right away will cook the pizza at temperatures ranging from room temp on up to 400F, increasing at an unknown speed. For a slow-heating oven, it might not hit 400f until the 10 minute mark, meaning your pizza will be kinda warm in places with a couple of bubbly bits of cheese here and there if you're lucky.

If your oven heats up instantly (and none do), it's not an issue. The only real way to tell is to put an oven thermometer inside where you can see it through the window. If you have an oven that measures internal temp separately from how you've set it, that can work, too. Once either thingy reads 400, insert pizza.

Failing all of that, you can always, you know, follow the directions.

Edit after re-read of OP: no, it doesn't mean "get oven to 400F then leave it there for 10 minutes". It means "turn oven on, set to 400F, then walk away for 10 minutes until you're really sure that the internal temp now measures 400F".
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Re: Does it matter how long I preheat my oven?

Postby Sir_Elderberry » Sat Jun 19, 2010 5:17 am UTC

Nearly every oven I've seen has you enter the temperature, and then you walk away, and you come back when it dings that it's at the correct temperature. The fact that you do not cook while "pre"heating is always a given.
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Re: Does it matter how long I preheat my oven?

Postby poxic » Sat Jun 19, 2010 5:22 am UTC

Note to the spoiled younger generation: not all ovens ding when they're at temp. Not all ovens can even tell you when they're at temp, beyond maybe the "actively heating now" light going out for a bit.

/lawn etc
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Re: Does it matter how long I preheat my oven?

Postby Spot » Sat Jun 19, 2010 5:45 am UTC

poxic wrote:Note to the spoiled younger generation: not all ovens ding when they're at temp. Not all ovens can even tell you when they're at temp, beyond maybe the "actively heating now" light going out for a bit.

/lawn etc

That I did not know. And it seems to explain the confusion I had. I was thinking, "why should I wait ten more minutes after the oven has beeped to tell me that it's at 400?"

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Re: Does it matter how long I preheat my oven?

Postby Thesh » Sat Jun 19, 2010 6:07 am UTC

Does it ask you to have a pan in it first? If so, they might just be making sure the pan itself reaches 400 and not just the air inside the oven. I know when I cook steak, the oven reaches 500 long before my cast iron skillet does.
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Re: Does it matter how long I preheat my oven?

Postby KyleOwens » Sat Jun 19, 2010 7:44 am UTC

I believe Alton Brown explained this a while back. Basically his reasoning was that while the area near thermostat might reach 400 in a few minutes it doesn't necessarily mean the rest of the oven has come up to temp. Waiting the full 10 minutes helps ensure that all the walls are fully heated so that when you open you oven to put the pizza in there's less of a temperature drop.

I'd also like to add that oven thermostats are usually horribly inaccurate and that extra 10 minutes might be there just because you shouldn't trust it to be right as soon as it says 400.

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Re: Does it matter how long I preheat my oven?

Postby Ended » Sat Jun 19, 2010 9:46 am UTC

poxic wrote:Note to the spoiled younger generation: not all ovens ding when they're at temp. Not all ovens can even tell you when they're at temp, beyond maybe the "actively heating now" light going out for a bit.

/lawn etc

Indeed. At my lodgings we have an old gas oven with none of these mod cons like a "thermostat" or "lights" or a "working igniter" (that last one is pretty dangerous, actually). Cooking goes something like: 1) Turn on gas to required level 2) Light gas with match 3) Wait around a bit 4) Put something in.
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Re: Does it matter how long I preheat my oven?

Postby Charlie! » Sat Jun 19, 2010 1:38 pm UTC

The thermostat in most ovens measures the air temperature, which is good enough for most stuff. But the walls, which help cook because they radiate, warm up a little slower, so if you let the walls warm up you'll cook your pizza a bit faster, which is good for it.
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Re: Does it matter how long I preheat my oven?

Postby brakos82 » Sat Jun 19, 2010 5:02 pm UTC

poxic wrote:Note to the spoiled younger generation: not all ovens ding when they're at temp. Not all ovens can even tell you when they're at temp, beyond maybe the "actively heating now" light going out for a bit.

/lawn etc


I still have a yellow oven from the 70s, and it clicks.
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Re: Does it matter how long I preheat my oven?

Postby Kow » Sat Jun 19, 2010 11:43 pm UTC

KyleOwens wrote:I believe Alton Brown explained this a while back. Basically his reasoning was that while the area near thermostat might reach 400 in a few minutes it doesn't necessarily mean the rest of the oven has come up to temp. Waiting the full 10 minutes helps ensure that all the walls are fully heated so that when you open you oven to put the pizza in there's less of a temperature drop.

I'd also like to add that oven thermostats are usually horribly inaccurate and that extra 10 minutes might be there just because you shouldn't trust it to be right as soon as it says 400.

This man speaks the truth. This is the same reason that many people keep pizza-stones and bricks inside their oven. It allows for a more even and consistent temperature. When your oven says it's at temperature, you can be assured (if it's a good oven) that the air temperature inside the oven is, but as soon as you open it, a large portion of that air is swept out by the door's movement. Keeping the oven at temperature heats more than just the air, allowing the oven, even during relatively long door opens, to maintain the desired temperature.
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Re: Does it matter how long I preheat my oven?

Postby Ouch.jars » Sun Jun 20, 2010 10:47 am UTC

brakos82 wrote:
poxic wrote:Note to the spoiled younger generation: not all ovens ding when they're at temp. Not all ovens can even tell you when they're at temp, beyond maybe the "actively heating now" light going out for a bit.

/lawn etc


I still have a yellow oven from the 70s, and it clicks.


I got a new oven last year that doesn't make any of those helpful noises.
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Re: Does it matter how long I preheat my oven?

Postby Bobber » Wed Jun 23, 2010 9:31 am UTC

To find out the temperature of an oven I was always told to slowly turn the temperature dial down until the "actively heating" light shut off, and that would be the approximate temperature that the oven was at. Thought thought I'd mention it.
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Re: Does it matter how long I preheat my oven?

Postby Adacore » Wed Jun 23, 2010 11:06 am UTC

I've never seen an oven that tells you in any sensible way when it's at temperature. I just work on the principle mentioned by Bobber to find the current temperature - rotate the temperature dial until the heating light goes off (or, if you're waiting for the oven to cool down, until you hear the thermostat click).

I don't think pre-heating is all that vital most of the time. So long as you're ok at cooking things that don't need much time by eye, which is easy with pizzas. For things that take longer to cook, the 5-10 minutes it takes for the oven to warm up make relatively little difference to the end result. One weird thing I have seen is some pizzas (I think they're certain Goodfella's ones in the UK) ask you to put the pizza in the oven without preheating, then give a set cooking time - there's no way that can be accurate, surely? I mean, it doesn't matter, when it comes to pizza, since I never even look at the cooking time and just gauge it by eye, but still...

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Re: Does it matter how long I preheat my oven?

Postby Moo » Wed Jun 23, 2010 11:51 am UTC

Adacore wrote:For things that take longer to cook, the 5-10 minutes it takes for the oven to warm up make relatively little difference to the end result.
Things that rely on delicate chemical reactions to rise, like some cakes and souffles, do definitely suffer from the inconsistent heating.
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Re: Does it matter how long I preheat my oven?

Postby Adacore » Wed Jun 23, 2010 12:50 pm UTC

Moo wrote:
Adacore wrote:For things that take longer to cook, the 5-10 minutes it takes for the oven to warm up make relatively little difference to the end result.
Things that rely on delicate chemical reactions to rise, like some cakes and souffles, do definitely suffer from the inconsistent heating.

That's true, I hadn't thought of that, not being much of a baker myself. I mostly use the oven for far too many ready meals, to be honest, although I do occaisionally branch out into other stuff; I've never dared attempt a souffle, and I'm not a massive cake afficionado.


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