For the next TTTT, I am going to put microwave popcorn in a test tube. Have you ever cut open a bag of microwave popcorn? It is nasty looking. It looks like something a cat threw up.
The test tube will be sealed up with an epoxy plug which will cause the internal pressure to increase as the heat increases. Popcorn pops because of the moisture inside the kernel. The shell of the kernel allows the pressure to build up inside. Eventually, the kernel can no longer hold the pressure and the pressure is instantly released. The moisture expands about 1600 times. The starches inside behaves like foam and expands and solidifies almost instantly.
Inside the test tube, the pressure inside the kernel will be about the same as the pressure outside the kernel. The popcorn will not pop. But, once the epoxy plug blows and the pressure drops to atmospheric pressure.... the kernels will instantly pop.