Re: [Phys-L] popcorn physics

[Bill Nettles <bnettles@uu.edu>]

> -----Original Message-----
> From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of Anthony
> Lapinski
> Sent: Tuesday, June 18, 2013 9:10 PM
> To: phys-l@phys-l.org; tap-l@lists.ncsu.edu; njaapt@mail.aapt.org
> Subject: [Phys-L] popcorn physics
>
> I was just microwaving some popcorn -- one of my favorite snacks. I can
> never get all the kernels to pop. Microwave the bag longer, and the popcorn
> starts to burn. This has been a problem I've notices for decades.

I'm sure you realize that there are "hot spots" in the microwave oven. Also, outer "moisture" will shield the inner. And there is a statistical distribution of the moisture content of the kernals.

Most (all?) microwave popcorn bags have some solid fat (and think lots of hydrogen-like bonds) which I suspect is the main energy catcher. The oil gets hot and surrounds the kernels, acting as an efficient heat source for the kernel.  As the melted fat is absorbed by the popped kernels, there are leftover kernels which don't get hot enough to pop, but the fat in the popped ones continues to absorb energy and reaches a temperature that scorches the white matter.

It would be an interesting experiment to put some popcorn in a bag with NO fat and see how much popping one gets. Looking at all hypotheses: 1) more popping, 2) less popping, 3) same popping, 4) no popping, and then a) even popping b) uneven popping.

I do know that you can pop popcorn using hot air without oil.  I can't remember what happens if you try to pop with direct heat over a flame or in a dry pan.  I think the popped kernels burn quickly in those "open flame" baskets.