Put the watermelon on its side on a cutting board and use a large, sharp knife to carefully slice off about 3/4 inch from its top and bottom.
Look at the Watermelon “Popsicles” recipe. Do you think the watermelon will stay the same after freezing as the fruit you are used to eating? What might be different about it?
Aside from being much colder, the ice pops are also solid and brittle. The transition from soft fruit to frozen not only makes a delicious treat, but also illustrates an important scientific concept.
Watermelon, as you can guess from the name, contains a large amount of water. This means that it behaves a lot like water does at different temperatures. At room temperature, water is a liquid; water molecules are moving around freely in the fruit, producing a soft, juicy texture. When you put the melon in the freezer, the water molecules slow down a lot, eventually forming solid ice crystals that give the fruit a Popsicle-like consistency.
The change from liquid to solid is known as a phase transition. These transitions are important in the kitchen, and appear in everything from cooking eggs to making ice cream. Can you think of other examples? Understanding how and why things happen in the kitchen can make you both a better chef and a better scientist—at the same time!