Re: Why will a single kernel of popcorn not pop by itself in a microwave?

Hi, Nicole!

Popcorn "pops" by the pressure of steam building up inside the enclosed 
kernel. The steam forms by heating the small amount of water remaining in 
the kernel.

The amount of water in the kernel is important for good "popping". If 
there is too much water, the kernel is too soft and gives way slowly 
instead of exploding. If there is too little water, the steam pressure may 
not be great enough to cause the explosion.

The reason that popping loose kernels of popcorn in the microwave is 
difficult is that the absorption of microwave energy is only due to the 
residual moisture in the corn. Commercial popcorn bags have metallized 
film to capture a much larger amount of energy, and oil to conduct it to 
the popcorn. Higher energy per unit time means a higher temperature and a 
much higher steam pressure.

Without the rapid rise in temperature coming from the metallized film, the 
kernels may give way slowly instead of exploding. 

I hope this answers your question!