In this issue:
Science applies to almost all of life, even to cooking and eating. Chemical reactions and changes are happening all the time in the kitchen, from bread rising to sauce thickening. Do the following projects to explore the fascinating properties of eggs and have some fun with science you can eat!
Egg in a Bottle
Learn about the relation of temperature to pressure as you watch an egg get sucked into a bottle. This project requires adult supervision.
>> Watch our video demonstration, and then try it yourself!
First, the science behind a hard-boiled egg: Egg whites are made of water and proteins. Proteins are made of long chains of amino acids, but in an egg the chains are clumped tightly together in individual spheres. (These are called "globular proteins.") When the egg is heated, the proteins and water molecules begin to move faster. As they move and collide with each other, the individual protein chains start to "unravel," eventually bonding loosely with other protein chains, forming a network of protein with water trapped inside. The consistency has changed from runny egg white to a soft solid!
So how does this squishy-but-solid egg get mysteriously pushed inside the bottle? The answer is all about air pressure. When you first set the egg on the bottle, the air pressure inside the bottle matched the air pressure outside, so nothing happened. When you dropped the burning paper into the bottle, it caused the air inside to heat up and expand rapidly. That expanding air pushed the egg aside and escaped from the bottle; that's why you saw the egg vibrating. When the fire consumed all the oxygen inside the bottle, the flame went out and the remaining air in the bottle cooled down. Cool air takes up less space, exerting less pressure inside the bottle. (The egg acted as a seal to prevent outside air from getting in to fill the extra space.) The result was an unbalanced force—the force of the air pushing on the egg from outside the bottle was greater than the force of the air pushing up on it from inside the bottle. Voila - the egg was pushed into the bottle!
How do you get the egg out again? You need to increase the pressure inside the bottle. Turn the bottle upside down and tilt it until the small end of the egg is sitting in the mouth. Now put your mouth close to the bottle and blow, forcing more air into the bottle and raising the pressure inside. When you take your mouth away, the egg should pop out - just be careful it doesn't hit you in the face!
Green Eggs & Ham
When you were little, you probably read the Dr. Seuss book Green Eggs & Ham. Here's a little pH trick to make some green eggs just like in the book.
Red cabbage contains pigments called anthocyanins, which change colors when they come in contact with acids (low pH) or bases (high pH), making them a natural pH indicator. When the cabbage juice comes in contact with an acid (like vinegar) it will turn red, but when it is mixed with a base it will turn bluish-green. What does this project tell us about egg whites, then? Egg whites are basic (also called alkaline) and so they turn the red cabbage juice green.
Fizz Wizard & Jammin' Jelly Kit
This fun kit introduces basic chemistry concepts through making incredible and tasty concoctions like soda pop and pudding. The chemicals are all food-safe, so you can eat the experiments when you're done! In the process, learn about pH levels and polymers, concentration of solutions, and chemical reactions. The instructions explain the science behind these 16 fun experiments. Some household items are required, such as sugar, lemon juice, and milk. Ages 8 & up.
Is it possible to put ice cream in a hot oven without it melting? Oh, yes! Make this delicious dessert to try it out. There are many variations of this dessert—choose the type of cake, ice cream, fillings, and toppings that you like best. You can make one large dessert, or individual ones as we did.
*Safety note: Sometimes the egg whites in the meringue won't be fully cooked. If you're concerned about salmonella, use pasteurized dehydrated egg whites or meringue powder you can buy at the store. You can also use liquid pasteurized egg whites from a carton, although the meringue won't fluff up as much as with fresh eggs.
In the first experiment, we saw eggs change their form when heated. In this recipe, we see that egg whites also change their form when beaten vigorously! The two changes are caused by the same thing: globular proteins unfolding and forming new bonds with each other. When you beat the eggs, you're adding air bubbles to the mixture of proteins and water in the egg whites. Some of the amino acids in the proteins are attracted to water and some are repelled by it. The proteins begin to unfold so that the water-loving amino acids can move towards the water, and the others can move toward the air pockets. The unfurled proteins bond with each other, creating a network of protein that traps the air bubbles inside, making a nice fluffy, frothy meringue.
Now, the ultimate question—why didn't the ice cream melt completely when you put it into that very hot oven? The answer is that the meringue acted as an insulator, slowing down the transfer of heat. It works kind of like styrofoam (but tastier); the air trapped in small pockets in these materials makes them both good insulators.
More Edible Science Projects:
- When egg whites are beaten, they take up 6-8 times more space than liquid egg whites!
- Baked Alaska got its name in the 1870s, but some form of the dessert had been around for much longer. A guest at the White House in 1802 (during Thomas Jefferson's presidency) described eating a dessert of ice cream inside piping hot pastry.
Watch the egg in the bottle experiment in action with the HST project video.
Learn more about the science of eggs and other foods at the Exploratorium Museum's cooking science site.
Why do foods brown when they cook? What is flavor? Find the answers to these and other cooking science questions at Science of Cooking.