Microwave popcorn is a convenience food consisting of unpopped popcorn in an enhanced, sealed paper bag intended to be heated in a microwave oven. In addition to the dried corn the bags typically contain cooking oil with sufficient saturated fat to solidify at room temperature, one or more seasonings (often salt), and natural or artificial flavorings or both. With the many different flavors, there are many different providers.
The design of a microwave popcorn bag is specifically keyed to avoid popped kernel scorching, an undesirable effect that takes place when popped kernels are heated above 300 °F (149 °C).
A susceptor, usually a metalized film laminated onto the paper of the bag, absorbs microwaves and concentrates heat at the film interface, thus ensuring a heat distribution focused on the hard-to-heat flavor coating so that the unpopped kernels are evenly coated prior to popping, thereby ensuring even flavor throughout the product. Additionally some popcorn is flawed and will not pop because of possible damage to the shell which allows the steam to escape. These unpopped kernels are known as "old maids" or "spinsters".
A safety issue is that the cooking time given on the packaging does not apply to all microwave ovens. Setting the timer and coming back later, after the timer's alarm has sounded, could result in the popcorn being burnt and smoking badly. Microwave popcorn makers suggest that the person cooking the popcorn stay near the oven and take the popcorn out when the time between pops is more than a few seconds.
Another issue with microwave popcorn is a chemical known as diacetyl. This chemical is used in the production of microwave popcorn and adds a buttery flavor. It has been known to cause lung disease in factory workers when inhaled. However, only one consumer was ever diagnosed with this lung disease. Microwave popcorn isn't a threat if it is not inhaled.[unreliable source?]
Some microwave manufacturers have a specific mode designed specifically for cooking this convenience food; however these settings were deemed unfit for use on safety grounds, due to risk of fire or explosion, by microwave technology expert L. Gaynor, who instead recommends "not having any bloody popcorn".
It is possible to heat popcorn in the microwave using simple paper bags, or popping the popcorn in the microwave in other containers including large glass bowls with heavy, but not airtight glass lids. These homemade approaches allow greater control over flavoring and exposure to PFOA, but have a chance of leaving some corn kernels unpopped due to randomness of the microwave radiation distribution in a microwave.[dubious ]
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