Things That Expand in Microwaves

Popcorn

• Popcorn kernels appear dry, but each kernel contains a tiny drop of water. When heated in the microwave, this water turns to steam. The pressure from the steam is so great that it turns the popcorn kernel inside out, creating the fluffy popped kernel enjoyed at movie theaters. Microwaves heat only the water in the popcorn and will not burn the popcorn, unless you have a bag of microwave popcorn containing too much popping oil. The oil gets hotter than water and will cause the popcorn to burn. To avoid this, pop the popcorn in a paper bag folded over without oil for two to three minutes, or until you hear the popping sounds slow down.

Marshmallows

• Heat a marshmallow in the microwave for one minute and it will double in size. This occurs when water in the marshmallow converts to steam. The air holes in the structure of the marshmallow fill with this steam, like tiny balloons, and get bigger, causing the entire marshmallow to expand. Try microwaved marshmallows for an indoor version of s'mores to view the expansion of these candies.

Bread Dough

• Microwaves can be used to proof bread dough, but in this instance, instead of the steam from heating the water causing the dough to expand, it is carbon dioxide produced from the yeast in the dough. Yeasts are living organisms, and they need sugar added to bread dough to eat. Once they eat, the yeasts expel a small amount of carbon dioxide and reproduce, making more carbon dioxide-producing yeast. During proofing, which occurs fastest in a warm environment by briefly heating the dough in the microwave, the carbon dioxide from the yeast causes the dough to rise. Proof bread dough in a bowl next to a cup of water for eight minutes at 10 percent power, let the dough rest for five minutes, and heat again at 10 percent power for eight minutes or until doubled in size.

Bar Soap

• Heat a bar of Ivory soap in the microwave on a paper plate for two minutes on high power, and the soap bar will blow up into tiny soap flakes. This can be done only with soap bars that have enough air in them to float on water. The air bubbles in the bar of soap expand and blow the bar apart, causing the flakes to expand out of their original bar shape. This will not damage your microwave, just give it the smell of soap inside. The flakes should stay on the paper plate, but just wipe the inside of the microwave oven with a damp towel to clean any soap residue away. The bonus of this experiment is after rinsing away the soap flakes, you microwave interior will be freshly cleaned.