When do you need to pre-heat the oven?

August 30, 2013 3:57 PM

Is it always necessary to pre-heat the oven?

Help settle a debate between my boyfriend and I - He thinks that you should always pre-heat the oven when cooking; I think that pre-heating is important when you are baking, but not so much other times. When is it important, and when is it ok to go without? Feel free to explain the science behind your reasoning.

posted by 5_13_23_42_69_666 to Food & Drink (21 answers total)

No, it is not always necessary. In some cases, it is better not to, like in this recipe for cooking bacon in the oven (the #1 hit for "cook bacon in oven" on Google).
posted by procrastination at 3:59 PM on August 30, 2013 [2 favorites]

For meat, it's better to minimize the time in the "danger zone"-- between refrigerator temps and cooking temps. Plus, ovens heat up at different rates, so it's easier to time based on starting at a given temperature.

But yes, it's better not to for some things that are better with gentler heating-up.
posted by supercres at 4:00 PM on August 30, 2013

If you don't preheat the oven, then you don't have control of the temperature you're cooking the food with. Is there some sort of advantage to not having control over the food you're cooking?
posted by oceanjesse at 4:01 PM on August 30, 2013 [17 favorites]

I don't preheat the oven when I'm doing things like roasting veggies and/or potatoes; don't use a timer either. I'm just wanting them to get browned up and cooked through, so I don't see a reason for preheating and timing and all that jazz.
posted by NoMich at 4:06 PM on August 30, 2013 [1 favorite]

Best answer: For baking, pre-heating is often obligatory. Yeast bread, for example, should only rise that much, and then bake. If you put the half-risen bread into a warming-up oven, you lose control over the process and maybe your bread just deflates before baking.
A soufflé needs to bake immediately when put in, so even here the oven needs to be hot.
Fish has a short cooking time; pre-heating helps getting the timing right and prevents drying out etc.
A slow beef roast, on the other hand, can go into the cold oven, no problems.

In short, it totally depends. This is no "disagree with my boy/girlfriend"-material at all.
posted by Namlit at 4:06 PM on August 30, 2013 [6 favorites]

I can only think of a few things - like the aforementioned Bacon Method - that benefit from not pre-heating. When I'm roasting things on very high heat - be it chicken or brussels sprouts - I don't want time for it to get mushy or sweaty on the way to 450. I don't want my frozen pizza thawing and slowly sinking through the grate before the crust starts to cook.

I wouldn't stress too much if it was casserole-ish - made of mostly pre-cooked or raw-consumable ingredients that will cook for a long time and are meant to meld together, but I wouldn't deliberately start mac and cheese in a cold oven or anything.
posted by Lyn Never at 4:07 PM on August 30, 2013 [5 favorites]

It sometimes doesn't matter, but usually it does. So your boyfriend is mostly but not entirely right.
posted by bearwife at 4:09 PM on August 30, 2013 [1 favorite]

You want to pre-heat if you're cooking in a pyrex or ceramic baking dish. They can shatter if your oven heats unevenly.
posted by Blue Jello Elf at 4:10 PM on August 30, 2013 [1 favorite]

Best answer: Lack of preheating tends to make things soggy. Sometimes this is a neutral, like casseroles, but most of the time it's a negative. I make a lot of baked potatoes, and I used to just stick them in the cold oven but I've been amazed at how much better they are -- cooked more evenly, skin crispier -- when I preheat the oven.

My general thought is that 90% of things absolutely need the oven preheated, and about 98% of things are better when the oven is preheated, so I usually preheat the oven.
posted by jaguar at 4:14 PM on August 30, 2013

When you're following a recipe.
posted by humboldt32 at 4:18 PM on August 30, 2013 [1 favorite]

I agree with you. There are a lot of applications where it doesn't matter. I think it's primarily things with longer cook times and no particular need for getting things crispy are where it's not tht important.

Baked potatoes, lasagna, it's not really that important. If the debate is 'always' versus 'sometimes' then I think 'sometimes' wins.
posted by A Terrible Llama at 4:21 PM on August 30, 2013 [1 favorite]

Think of it as the difference between steady state conduction and transient conduction. Cooking your food is a math problem. Which differential equation is easier to solve?
posted by oceanjesse at 4:25 PM on August 30, 2013 [1 favorite]

It depends on what you're cooking. If it's something that's delicate or easily dries out, like fish or pork chops, you should pre-heat. You don't want to overcook them. If it's something you can set and forget (like a baked potato), pre-heating doesn't really matter.
posted by hooray at 4:46 PM on August 30, 2013

Response by poster: Think of it as the difference between steady state conduction and transient conduction. Cooking your food is a math problem. Which differential equation is easier to solve?

please elaborate!
posted by 5_13_23_42_69_666 at 5:34 PM on August 30, 2013

When it's important:

If you want a good crust on your homemade bread it helps to try replicating the steaming ability of commercial ovens. One way of doing this is preheating a hot (450+F) oven for a good solid half-hour or more with a pan on the oven floor. When you put the bread in you throw a handful of ice cubes in the bottom tray and quickly close the door, creating a quick burst of steam.
posted by Room 641-A at 5:34 PM on August 30, 2013 [1 favorite]

You want to pre-heat if you're cooking in a pyrex or ceramic baking dish. They can shatter if your oven heats unevenly.

No amount of uneven internal preheating will cause a spatial or transient gradient in temperature greater than inserting the object into a preheated oven, unless you're in the habit of easing dishes in literally at a snail's pace.
posted by Mapes at 5:35 PM on August 30, 2013 [3 favorites]

Yeast bread, for example, should only rise that much, and then bake.

Actually the bread example is a good one - because it's much, much more controversial than that.

There has been much, much discussion about this at The Fresh Loaf.

Long story short: It makes much less of a difference than you would think; many recipes call for no pre-heat; and many recipes that don't call for it can be successfully cooked with no pre-heat. In addition to those links, I would call myself an experienced home baker, and I can personally that pre-heating is not actually necessary for the majority of loaves.
posted by smoke at 5:49 PM on August 30, 2013

Best answer: 5_13_23_42_69_666: "please elaborate!"

I'm not the original poster of that comment, but it goes something like this: Say that "done" means a certain amount of energy has been added to the food. Let's simplify and say that that energy is in units of degree-minutes, so ten degrees at 350 is 3500 degree-minutes. In the case of a pre-heated oven, you know that the energy (this is radically simplified) is as above, duration times temperature.
If you don't pre-heat, it's much more difficult to determine the amount of energy added to the food - even assuming your oven pre-heats at a set rate, it's a pain in the ass to figure, and you'd have to experiment to find out what the heat-up rate is.
posted by notsnot at 6:54 PM on August 30, 2013

Best answer: Well if you think of the forces acting here, the heating element is on the bottom, and while the oven is preheating, all of the heat is rising directly up and heating the bottom disproportionally. Once the oven is preheated, the bottom heating element only kicks back in when the temperature within the oven falls below a certain point, and the temperature jumps around plus or minus a few degrees or so. If you take the mean of those oscillations over a given wave period, you can say that the temperature of the oven is at a predictable steady state. Before the oven is at a steady state, the heat coming from the bottom is disproportionally heating the bottom of the baking container, and there is a more sharp 3D temperature gradient that makes some parts of your food get heated up much more than others. When the temperatures are changing like that, and there is no steady state, some method of accounting for this "transient" heating process must be accounted for within the cooking process unless your food has some weird geometry that would allow you to advantageously take advantage of the stronger 3D temperature gradient cooking different parts of your food to different preferred temperatures. You could model this thermal system with something called the Finite Element Method. So maybe if you had the right heating conditions, food geometries and material properties, and oven geometries and material properties calculated (maybe even some fans, lasers, or microwaves for kicks, too), you could likely set up pie á la mode to be warmed up without melting the ice cream, but I doubt that's what you two have been arguing over. You probably just want everything to heat evenly so that you don't end up jumping into partial differential equations and computational models to cook your dinner perfectly, and this is what makes preheating nice. It reduces dimensionality.

Did any of that make sense? It's a little late on my end, and this is coming out of a cell phone.
posted by oceanjesse at 11:11 PM on August 30, 2013 [1 favorite]

Meat which is to be well-done can go in a cold oven - I find chicken gets better that way. But otherwise, not really
posted by mumimor at 12:42 AM on August 31, 2013

Response by poster: you guys are the best!
thanks for the amazing answers
posted by 5_13_23_42_69_666 at 12:48 AM on August 31, 2013