How hot does popcorn need to be before it pops?

Some kernels would pop, but generally speaking it would not work very well at all. A popcorn kernel pops because of the water trapped inside -- it is heated rapidly on the stove, and its expansion is rapid enough to produce explosive force. The oven would cause the water inside the kernels to heat more slowly. The shell of unpopped corn is not perfectly enclosed, so slow heating would allow the water vapor to harmlessly escape.

You need to get the popcorn kernels up to about 175–180°C internal temperature fairly quickly (but possibly not too quickly; the starch needs to cook). A very heavy preheated roasting pan could do that, probably.

But then you've got another problem. Normally, in a stovetop popper, the popped kernels "float" to the top. And they have very little contact with the bottom of the pan after that (where the heat is coming from). They thus fairly quickly cool (as all the water in them flashes off). In the oven, the heat comes from all around, and thus they'd continue to heat to your 250°C oven temperature. In other words, they'd probably burn.

If you want to try it, I'd recommend (a) good ventilation; (b) make sure the cover is on well—they explode with some force; (c) fully preheat a very heavy pan; (d) pull it from the oven the second popping starts to prevent burning; (e) shake from side to side while its popping. I'm interested in hearing your experimental results.

Ovens generally convey heat too slowly to be ideal to pop popcorn to understand why let's get into the science of how popcorn pops.

Popcorn pops that the boiling point of water inside the kernel at popping pressure. This is NOT 100 degrees Centigrade or 215 Fahrenheit. That is the boiling point of water at sea level air pressure (i.e. 1 Atmousphere pressure.)

The steam needs to reach much higher pressure to burst the kernel open, and thus needs a higher temperature to create steam to the pressure. (much like inside pressure cooker.) The pressure needs to reach roughly 135 PSI (~9 bar), or 9-40 times the pressure of a consumer pressure cooker (depending on model and design.)

The temperature at which this pressure is reached is roughly 180-200C or 350-390F. Yes, these numbers don't match up, they are just the nice round numbers referenced.

You may note that the temperature is well over the smoke point of butter, yeah, don't use butter. If you like butter, you'll have to use clarified butter, and the stuff you clarify yourself probably won't be good enough unless you are a 5 star chef so you'll have to buy the fancy stuff. Butter can go on afterwards as a flavoring.

Back to the point, as of why popping in the oven doesn't work well, you CAN pop popcorn in an oven, but that doesn't mean it's advised to. An oven will heat the oil too slowly, and thus heat the popcorn too slowly. The result of this is the steam escaping before it reaches critical pressure, and getting a lot of old maids, meanwhile the popped popcorn will spend too much time at cooking temperature and fry in the oil or otherwise cook and burn. Hence you will get a lot of burnt popcorn. It just doesn't make good popcorn.

The method I prefer is using an induction burner or some other thermostat controlled burner. However, you can use an oven burner (electric or gas) if you don't and use medium heat taking care not to burn the oil, and thus ruining all the popcorn.

For a cooking container I like a stainless steel bowl, other people prefer an enamel steel pot or cast iron. You need a lid, but if you don't have one, Aluminum foil is always a good substitute. Have a second container of roughly the same volume, or slightly bigger ready to pour the popcorn into.

There are two different preferred methods here, just use the one that works for you.

If you want to preheat the oil, which works best with larger and heavier cooking vessels heat the fat you like to it's cooking temperature (maximum temperature under the approximate 215C/420F where the starch will start burning way too easily, and smoke point of your oil, whichever is lower. I use 190C/375F myself, which works fairly well. When the oil reaches temperature (as determined by a thermometer, or your preferred method. You can always throw in a kernel to check. It should pop in a few seconds.)

Once the oil is ready you should throw in the kernels, enough to layer 3-4 layers over the oil, or enough to pop the container full of popcorn, whichever is less (obviously).

Throw the lid on, and shake the container periodically on the burner to keep popcorn from being stuck. Once the popcorn slows, or the container lid is being pushed off, pull it from the heat, and dump out the popcorn goodness.

To do the non-preheat method you need a powerful burner, a smaller container, and/or a thermostat controlled burner. Preferably all three. You throw the popcorn in at the start and heat like before. Shake it every 30 seconds or so until it starts to pop, then continue as before.

After you are done cooking the popcorn, add your favorite flavorings, be it fake butter flavor, real butter, salt, caramel or any of the more exotic flavors out there. There is Coco, Hot Pepper, Balsamic Vinegar, Malt Vinegar, fish oil, peanut butter, garlic, pesto spices or whatever suits your taste, there's plenty of crazy toppings out there, and if you ever run out of ideas you have a whole world of information online to find more ideas on. You have to love the information age.

As for an additional tip My favorite two fats are peanut oil and high-grade refined clarified butter. Since clarified butter is more expensive in the US, being a specialty product mainly bought by hipsters looking to impress their date and peanut oil is dirt cheap oil bought by us worker drones who like to fry our own fries at our BBQs, I tend to use peanut oil unless it's a special occasion. I hear that in Europe and Asia clarified butter is easier to get a hold of for a decent price. I don't know if that's true, but it might be good.

Popcorn kernels burst because the water trapped inside expands and superheats into steam. While it is technically possible for popcorn kernels to pop at 100°C (212°F), it is much more likely to pop at higher temperatures, usually around 150°C, because the water rapidly heats up and steam doesn't have much time to escape, instead bursting open the kernel and "popping".

The 250°C you specified is more than enough to pop popcorn kernels. As for if an oven would work, it might. Convection ovens are the best for popping popcorn, for their even heat distribution and dry air, as well as their ability to whisk away moisture from popping kernels' released steam.

This worked for us: open the oven at 210°C. Close the door and wait for the first pop (about 5 mins), then open the door and stir, close the door again and watch it pop until finished. Or microwave for about 10 min. or until the popping finishes.

This work for me: open oven at 230°C. No oil, no butter and no thick pan needed, only using normal thin tray, open both top and bottom oven burn mode, waiting for about 3 mins heating, then pour the seeds in. Close the door, waiting for first pop (about 5 mins), then open the door and stir, close the door again and watch it pop until finish. The temperature at the tray was about 195°C when it pop (I have measured). 250°C may be too high a little. I guess 240°C is the best.

UPDATE:

• I'm using electric oven.

• The tray I used was fit inside the oven to handle all popped seeds. You can use metal container with cap like covered roasting pan. However it will need more time preheat for preparing high temperature enough. Also, if the pan was too small or too thin, the heat it transfers to the seeds will not enough, thus will decrease both percent popping and quality popcorn.