Without moisture -- 13.5 percent to 14 percent per kernel is needed -- popcorn can't pop. That's why it's important to store popcorn correctly. An entire percentage of moisture can be lost if your kernels are left uncovered on a hot day. And though that may not sound like a lot, it adds up. A loss of 3 percent can render popcorn unpoppable. And even a 1 percent drop in moisture will harm the quality of your kernels.
So what's the best way to store popcorn? Airtight containers -- plastic or glass -- are your best bet to avoid moisture loss, especially when stored in a cool place like a cupboard. http://www.ellispopcorn.com/All%20about%20popcorn.htm
Avoid the refrigerator. Some say the cold storage makes the popcorn taste better, but many refrigerators contain little moisture and can dry out kernels.