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My roommate and I were wondering why 1 bag of unpopped popcorn is reported to have more calories/fat/sodium/protein/fiber than when the bag is popped. We have looked it up, with mixed results. Some people have said it's because there is butter left over on the inside of the bag after popping, but this particular popcorn only has oil in it, which wouldn't explain the change in fiber or other nutrients. Another explanation was that since only about 85% of kernels actually pop, the popped nutrition facts don't account for the other 15% of kernels. What do you think?
After a fair amount of research into this I must admit that I am not sure what you mean. Possibly you have a microwave popcorn product that I am not familiar with but I have not been able to find one with nutrition facts from the pre vs. post popped popcorn.
That said, there might be a few explanations. There are a number of ways that the calorie counts, etc. are measured for reporting purposes. The most common, called a Calorimeter, uses chambers that measure the caloric value of a product when it is heated.
I might assume that the popcorn changes slightly when popped as anything does by releasing some energy. The easiest explanation is that the energy from the heated oil is released and changes the chemical composition of the mixture slightly. And yes, your idea that all of the kernels don't pop might be a good one.
All of that said, you don't need to use the microwave popcorn bags to make great popcorn. The kernels will pop well on their own in a brown paper bag — cheaper, healthier and still with a lot of fiber. Here's how you can make caramel popcorn at home using either prepackaged microwave popcorn or popcorn you've popped in a brown paper bag.
Thanks for writing,
Timothy S. Harlan, MD, FACP