July 14, 2004

How Long Does It Take to Freeze?

Explorers used Antarctica as a giant freezer. All that ice and cold made it very easy to keep their food from rotting. But different foods take different amounts of time to freeze, and some foods taste pretty bad once they've been frozen and then thawed. How long do you think it takes an egg to freeze? How about a glass of milk? You don't have to live in the Antarctic to find out—you can test this right at home in your freezer. This activity uses foods that the explorers brought along on their trips. They got their eggs from live chickens they brought with them.

Materials

• Adult supervision required
• 1 raw egg
• 2 small freezer-safe glasses or cups
• 1 piece of bread (about 1/2-inch thick)
• Small freezer-safe plate
• 1/2 cup milk
• Frying pan

1. Carefully crack the egg into one of the glasses or cups, being careful not to break the egg yolk.
2. Place the bread on the plate.
3. Pour the milk into the remaining glass or cup.
4. All of the foods, in their containers, should be about the same thickness or depth. Since the goal of this activity is to see which freezes first and which takes the longest to freeze, it's important to make things as even as possible. (For example, two separate cups of milk will take an equal amount of time to freeze. But what if you compared a cup of milk to, say, a whole gallon? The gallon of milk would take much longer to freeze!)
5. Place all three containers in the freezer. Make sure that the containers aren't touching each other or other foods that are already in the freezer.
6. Wait 30 minutes, then check to see if they've frozen. Do this by gently poking each one with your finger. Do this carefully so that you don't end up dividing the food into two parts, since then your freezable amounts will be smaller. Have any of them frozen yet?
7. Keep freezing the foods and checking on them every 30 minutes. When a food completely freezes, remove it from the freezer and note how long it took to freeze. (It may be a couple of hours or more before all of the foods freeze.)
8. Which food froze first? Which took the longest to freeze? Can you figure out why?
9. Now let each food thaw just enough so that you can bite into the bread and drink some of the milk. (Do not taste the raw egg.) Taste the bread. Does it taste good or bad? How about the milk? Ask an adult to cook the egg for you in a frying pan. When it's cooked, taste it. How do you like it?
10. Based on your taste test, which food would be the best to take to Antarctica?

Foods that are low in water content, such as bread, freeze quickly. When they defrost, they taste just fine. Foods that are liquid (very high in water content) develop ice crystals. They taste OK, but not great, when completely defrosted. Foods that are high in both protein and water, such as eggs, freeze relatively slowly, and they don't taste very good when they're thawed and cooked.

Activity excerpted by permission of Independent Publishers Group from Polar Explorers for Kids: Historic Expeditions to the Arctic and Antarctic with 21 Activities by Maxine Snowden. Published by Chicago Review Press, distributed by Independent Publishers Group (www.ipgbook.com). Copyright © 2004 by Chicago Review Press.

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