You have to study the grain. Most kernels have a left to right grain, and they will pop between 140-150C, because the cell structure of the skin is weak in several places. A relatively rare genetic mutation leads to around 1-2% of kernels having a right to left grain, and because of this orientation the skin is actually more robust in the typical popping spots, meaning that temperatures as high as 450C are required to pop these! That's why they typically will remain unpopped when cooking popcorn in this legacy manner.
To detect the right-to-left kernels, you can actually use a UV flashlight - you will see that they have a softer glow compared to the bright left to right kernels.
If this is true, does this mean that it's technically possible to pre-sort out most of the kernels that won't pop easily? Do expensive popcorn brands do this? Would it be possible to breed out this mutation? So many questions.
You have to study the grain. Most kernels have a left to right grain, and they will pop between 140-150C, because the cell structure of the skin is weak in several places. A relatively rare genetic mutation leads to around 1-2% of kernels having a right to left grain, and because of this orientation the skin is actually more robust in the typical popping spots, meaning that temperatures as high as 450C are required to pop these! That's why they typically will remain unpopped when cooking popcorn in this legacy manner.
To detect the right-to-left kernels, you can actually use a UV flashlight - you will see that they have a softer glow compared to the bright left to right kernels.
Hope that helps!