Popcorn is a special type of corn. Of the four
types of corn, popcorn is the only one that can pop. It is different
from other types of corn in that its hull, or outside covering, is just
the right thickness to allow it to burst open.
Each kernel of popcorn contains a small drop of
water stored inside a circle of starch. The starch is surrounded by the
hard hull. The hull does not allow water in or out of the kernel. When
you heat popcorn in the microwave, the drop of water in the kernel
starts to heat up too. Once the water gets hot enough, it changes into
steam inside the kernel. The steam makes the starch heat up and expand.
Once the starch has expanded to the hull, it continues to push against
it until the hull explodes. The starch rapidly cools when it comes into
contact with air, creating the familiar white puff that you eat. The
kernel swells to 40 to 50 times its original size.
Why does Swiss
cheese have holes in it?
To make cheese from milk, the milk is slowly
exchanged with bacteria. The bacteria makes lactic acid, which is
essential to the production of cheese. Different types of cheeses are
made using different bacteria, which is responsible for the different
Swiss cheese is made by adding a certain bacteria
to milk after it has been warmed. The bacteria forms curds in the milk,
which are pressed into heavy molds forming a cheese wheel. The Swiss
cheese is densely packed with a very thick rind. As the Swiss cheese
ages the bacteria inside continues to eat away at the cheese. The
bacteria “breathes” out carbon dioxide gas. Since the rind is so thick,
the carbon dioxide cannot escape and makes the holes for which Swiss
cheese is known.