Mythbusting: Preheating Ovens

Comments

Dougal Stanton \| 2008-11-12 12:32:17 UTC Can you give any indication of how long it takes for your oven to come to temperature against how long you were cooking things for. If it takes ten minutes to hit, eg 180C, and you’re supposed to give something 8 minutes at 180C, are you expected to do some oven calculus to tell how much “effective heating” the foodstuff has had? Also, don’t ever try bread in a cold oven. Even loading loaves onto a warm-to-the-touch tray is a recipe for bread-stuck-to-tray-itis. I always have my oven on full for at least an hour before loading bread in (it helps to heat the kitchen too). Would dearly love a stonking great stone to make the job easier/better.
Jean-Loup \| 2008-11-12 14:06:25 UTC I have to say, I was shocked the other day when I found out the sheer amount of electricity ovens take. Anything that makes them run for a shorter period of time is definitely a plus in my book. I also noticed that if I want, say 200 degrees, I have to set the thermostat just under 190 otherwise it’s just too hot (or maybe my oven thermometer is not well located..)
Hugh \| 2008-11-12 14:24:32 UTC @Dougal – Hmm. Should be doable in theory, but the maths would be pretty horrible. I certainly don’t have the math knowledge. Douglas B, are you reading this, and if so, what do you think? Bread – actually, there are some apparently very good cold-oven bread recipes knocking around. I saw this article in the NY Times for example. You’re right, though, if your recipe isn’t designed for it, bread in a cold oven is Epic Fail time. @Jean-Loup – yeah, ovens are horribly inefficient. It sounds like you actually have a comparatively accurate thermostat in yours (apparently electric ovens are a lot more accurate), but still… It’s one of the reasons I love sous-vide – you can do a lot of stuff with that that you’d normally do in the oven (long-cook meats, glazed carrots, etc), but it consumes a tiny fraction of the energy.
Stuart Carter \| 2008-11-12 15:43:31 UTC @Dougal: stick in a couple of bricks ;)
David \| 2008-11-12 17:26:02 UTC The math would be worse than you think. Not only would you have to do the calculus to figure out how much heat it’s getting, you’d need to also do the specific heat (sort of a heat capacity) for whatever it is that you’re cooking because that accounts for how fast the food absorbs the heat. Then if you have multiple things (like say sauce, cheese, and crust), each one has a different specific heat, and so heats up at a different rate. If you then factor in the inconsistencies just in the oven itself, it turns out to be pretty useless to have even done the math in the first place.
Leah \| 2008-11-13 13:34:31 UTC Reposting this here by request: I would say that for time sensitive things where the item has to be at that temp for a given amount of time, pre-heating is a way to increase the possibility that will happen. ;) Frozen pizza…isn’t one of those times. (They should have instead tried frozen chips for a better example.) What I am wondering is how convection affects things in the “empty pub”. I have an oven with convection. I should add that my oven is gas.
Hugh \| 2008-11-13 13:46:43 UTC Convection increases the flow of air around the oven, usually using a fan. That has two effects – first, it means that the oven will be much more even-temperatured than a non-convection oven, and secondly, it’ll increase the number of collisions between the hot air molecules and the food, meaning that it heats up quicker. Think about how much colder you feel in a stiff wind – same effect, but in reverse.
Liz \| 2008-11-14 13:49:20 UTC (Cross-posted from Hugh’s blog ’cause he asked me to.) Many, many years ago when I was doing home economics at school, we had a lesson about the importance of preheating the oven when baking. As a demonstration, we made Victoria sponge cakes – some people using preheated ovens, some not. All the preheated ones turned out fine, whereas the non-preheated ones didn’t rise much (if at all) and weren’t all cooked properly (some undercooked, some over). I suppose it’s possible that the teacher had somehow sabotaged half the cakes, but it doesn’t seem very likely. Also, if you’re doing Yorkshire puddings, you have to have the fat/oil very hot or it just doesn’t work. That said, I’ve done frozen pizzas in a non-preheated oven plenty of times and they’ve turned out okay. In conclusion, I’d say that it depends what you’re cooking, and you need to apply some common sense. If it’s a recipe where you can wing it, you can probably get away without preheating. And turn the oven on in advance (i.e. while you’re preparing stuff) so you’re not standing around waiting and getting irritated.
pajh \| 2008-11-14 14:56:38 UTC Liz: I’d completely forgotten about Yorkshire puddings. You’re right—-it’s fundamental to have the oil hot first.
Kytka \| 2008-11-17 10:28:34 UTC I think Liz is right – there are meals you don’t need to preheat the oven for and there are meals it is crucial to preheat the oven. Most of the time I switch on the oven first thing when I come to the kitchen, than prepare whatever is going in a then use it – not checking the temperature it already reached. Only if I consider the meal very tricky from this point of view, i wait until the oven reaches the correct temperature.

Make a comment

Edit | Back

Mythbusting: Preheating Ovens

We investigate cooking myths – do you really need to preheat your oven or is it just a waste of energy?

Length: 10 min

Links:

Credits:

Presented by Paul and Jehane Barbour

Also featuring Hugh

Petunia played by Lizzie Cass-Maran

Camerawork and Direction by Hugh Hancock and Stuart Brown

Motion Graphics, Editing, Compositing, Sound Design by Hugh Hancock

Pictures by

thekitchendesigner@ Flickr
Brett Neilsen @ Flickr
Lemoncat1 @ Flickr

(If we missed you out, please email us!)

Executive Producer: Hugh Hancock

License: Released under Creative Commons BY-SA-NC

Dougal Stanton \| 2008-11-12 12:32:17 UTC Can you give any indication of how long it takes for your oven to come to temperature against how long you were cooking things for. If it takes ten minutes to hit, eg 180C, and you’re supposed to give something 8 minutes at 180C, are you expected to do some oven calculus to tell how much “effective heating” the foodstuff has had? Also, don’t ever try bread in a cold oven. Even loading loaves onto a warm-to-the-touch tray is a recipe for bread-stuck-to-tray-itis. I always have my oven on full for at least an hour before loading bread in (it helps to heat the kitchen too). Would dearly love a stonking great stone to make the job easier/better.
Jean-Loup \| 2008-11-12 14:06:25 UTC I have to say, I was shocked the other day when I found out the sheer amount of electricity ovens take. Anything that makes them run for a shorter period of time is definitely a plus in my book. I also noticed that if I want, say 200 degrees, I have to set the thermostat just under 190 otherwise it’s just too hot (or maybe my oven thermometer is not well located..)
Hugh \| 2008-11-12 14:24:32 UTC @Dougal – Hmm. Should be doable in theory, but the maths would be pretty horrible. I certainly don’t have the math knowledge. Douglas B, are you reading this, and if so, what do you think? Bread – actually, there are some apparently very good cold-oven bread recipes knocking around. I saw this article in the NY Times for example. You’re right, though, if your recipe isn’t designed for it, bread in a cold oven is Epic Fail time. @Jean-Loup – yeah, ovens are horribly inefficient. It sounds like you actually have a comparatively accurate thermostat in yours (apparently electric ovens are a lot more accurate), but still… It’s one of the reasons I love sous-vide – you can do a lot of stuff with that that you’d normally do in the oven (long-cook meats, glazed carrots, etc), but it consumes a tiny fraction of the energy.
Stuart Carter \| 2008-11-12 15:43:31 UTC @Dougal: stick in a couple of bricks ;)
David \| 2008-11-12 17:26:02 UTC The math would be worse than you think. Not only would you have to do the calculus to figure out how much heat it’s getting, you’d need to also do the specific heat (sort of a heat capacity) for whatever it is that you’re cooking because that accounts for how fast the food absorbs the heat. Then if you have multiple things (like say sauce, cheese, and crust), each one has a different specific heat, and so heats up at a different rate. If you then factor in the inconsistencies just in the oven itself, it turns out to be pretty useless to have even done the math in the first place.
Leah \| 2008-11-13 13:34:31 UTC Reposting this here by request: I would say that for time sensitive things where the item has to be at that temp for a given amount of time, pre-heating is a way to increase the possibility that will happen. ;) Frozen pizza…isn’t one of those times. (They should have instead tried frozen chips for a better example.) What I am wondering is how convection affects things in the “empty pub”. I have an oven with convection. I should add that my oven is gas.
Hugh \| 2008-11-13 13:46:43 UTC Convection increases the flow of air around the oven, usually using a fan. That has two effects – first, it means that the oven will be much more even-temperatured than a non-convection oven, and secondly, it’ll increase the number of collisions between the hot air molecules and the food, meaning that it heats up quicker. Think about how much colder you feel in a stiff wind – same effect, but in reverse.
Liz \| 2008-11-14 13:49:20 UTC (Cross-posted from Hugh’s blog ’cause he asked me to.) Many, many years ago when I was doing home economics at school, we had a lesson about the importance of preheating the oven when baking. As a demonstration, we made Victoria sponge cakes – some people using preheated ovens, some not. All the preheated ones turned out fine, whereas the non-preheated ones didn’t rise much (if at all) and weren’t all cooked properly (some undercooked, some over). I suppose it’s possible that the teacher had somehow sabotaged half the cakes, but it doesn’t seem very likely. Also, if you’re doing Yorkshire puddings, you have to have the fat/oil very hot or it just doesn’t work. That said, I’ve done frozen pizzas in a non-preheated oven plenty of times and they’ve turned out okay. In conclusion, I’d say that it depends what you’re cooking, and you need to apply some common sense. If it’s a recipe where you can wing it, you can probably get away without preheating. And turn the oven on in advance (i.e. while you’re preparing stuff) so you’re not standing around waiting and getting irritated.
pajh \| 2008-11-14 14:56:38 UTC Liz: I’d completely forgotten about Yorkshire puddings. You’re right—-it’s fundamental to have the oil hot first.
Kytka \| 2008-11-17 10:28:34 UTC I think Liz is right – there are meals you don’t need to preheat the oven for and there are meals it is crucial to preheat the oven. Most of the time I switch on the oven first thing when I come to the kitchen, than prepare whatever is going in a then use it – not checking the temperature it already reached. Only if I consider the meal very tricky from this point of view, i wait until the oven reaches the correct temperature.