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Why is it that on some directions it says something like "preheat an oven for 400 for 10 minutes"?

Is it not enough to preheat the oven until the oven signals (i.e. usually with a beep) that the desired temperature has been reached? Are there any advantages to waiting longer even though the oven remains at the same temperature?

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4 Answers

There are some ovens out there that beep after a given amount of time, if they've hit the correct temperature or not.

Most of the residential ovens I've dealt with likely aren't at 400F within 10 minutes. It's possible that the recipe writer wants the dish going in before preheating is finished, but they have no way of knowing how long it takes your oven to heat up, so those instructions are going to give inconsistent results.

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Indeed, my oven does this. I finally got an oven thermometer the other day and tested it at 400° F. It set the timer for 6 minutes and beeped at the end. Going by the thermometer, it took nearly a half hour to actually come up to temp. –  Aaronut Feb 17 '11 at 16:13
    
@Aaronut: I am always astounded at how few people seem to realise the degree of need for the preheating of ovens. Your experience of half an hour is not unusual at high heats, and I regularly see people bung high-heat needing food in after 10 minutes or less. –  Orbling Feb 18 '11 at 2:34
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Many ovens, particularly older ovens, do not beep.

Indeed it is not uncommon that they have no temperature indication at all, particularly on gas ovens.

So the preheat timing for an oven is usually an indication from the author of the recipe that the oven needs preheating with a guide to how long you might wish to wait, usually intended as a minimum.

I have known some recipes to instruct food be put in the oven before temperature is reached for various odd reasons, that's not common, but does happen.

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I should've said 'indicate they're at temp' ... mine (electric) has a light (that goes off, to make it even more confusing), no beeping involved. –  Joe Feb 15 '11 at 1:48
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@Joe: My oven has no temperature gauge, indicator, or any other form of notification. There is obviously a control for the temperature, but no external notification as to whether or not the oven is at it. A thermometer has to be introduced to determine current temperature - this is not at all uncommon in gas ovens. –  Orbling Feb 15 '11 at 1:53
    
@Joe: Also. Shame, quite handy if it beeped for that. I use the timer clock on my oven a lot! –  Orbling Feb 15 '11 at 1:54
    
Not really, as most of 'em can't be trusted ... it's really safer to keep an oven thermometer and check .. as some go by time, if you have a pizza stone in there, they'll always be wrong. –  Joe Feb 15 '11 at 2:02
    
@Joe: Aye, too true. Why they bother including such a feature if it is timed, is a mystery. I suppose electric ovens usually have a fairly reliable heating profile. Gas ovens vary on local pressure, which varies depending on what other people in your neighbourhood are doing! Part of why I prefer electric ovens, but always gas hobs mind. –  Orbling Feb 15 '11 at 2:05
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When using a baking stone, for example for artisan breads and pizza, there are some additional reasons for the long preheat time.

With a baking stone, the recipe might advice you to preheat the oven for as much as thirty to sixty minutes. The reason is to heat the stone properly and to dry out the air inside the oven.

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If, like mine, your oven hasn't got a light, sometimes you can twiddle the temperature nob down until you hear a faint tick - that's the thermostat inside the oven clicking off. Where your temperature nob is at is the current temperature of the oven (at the thermostat, obviously). I keep checking using that technique every couple of minutes (remembering to reset the nob to my target temp between), until the tick is on or near the target temperature.

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