Originally aired during the week of December 27, 1999
For some of us, this is a prime season for cooking and eating (perhaps followed by a New Years' resolution to stop doing so much of the eating part.) Anyone who does a lot of cooking or baking is doing more than just slinging hash. They are really doing science! They just happen to wear aprons instead of lab coats. The holiday creations they whip up can be thought of as domestic science experiments. When you think about it, the kitchen is really a kind of "Epicurean Laboratory"... that happens to be the title of a book by Tina Seelig that discusses what's happening to our food on a molecular level when it is braised, whipped, mixed, heated or cooled. So this week on the program, chemistry class will be in session, with science experiments you can eat. Our first recipe: eggs - scrambled, boiled or fried.
Experienced cooks know that in order to make an omelet, you've got to crack a few thin-shelled, oval-shaped, protein-rich chicken ovums. Without studying a lot of chemistry, they also know when an omelet is cooked correctly by observing the color, texture, and consistency of the egg mixture. Eggs are liquid at room temperature but solidify permanently when heated, in contrast to sugar, fat, and water, which change from solid to liquid to gas stages. Egg whites are about 90 percent water and 10 percent protein. Heating an egg causes compact proteins to unfold into long, spaghetti-like strands. These strands release amino acids, which form bonds with other protein strands, causing coagulation. Overcooking creates too many bonds between proteins, leading to a rapid loss of liquid. That's the reason why overcooked scrambled eggs become rubbery.
We're talking about kitchen chemistry this week on the program. Today's subject is oil and water, which, we all know do not mix. Most types of molecules either dissolve easily in water, or in oil. But some substances, called emulsifiers, can enable oil and water to interact. Soap is a common household emulsifier. When soapy water comes in contact with an oily surface - say a greasy roasting pan - the soap forms bubbles around the oil droplets. The soap is also "hydrophilic" - it loves water - so soapy water can wash away the oil droplets along with the dirt they contain. Common cooking emulsifiers include egg yolk, ground mustard, or complex sugars. These ingredients don't allow oils and water to mix freely, but they do allow small droplets of one to remain suspended inside another.
Today we're taking time out for our kitchen chemistry experiment. The recipe: a liquid sandwich. You can't eat it, but it can make an colorful holiday centerpiece. Here's how you make it: find a small, thin bottle with a lid. Fill it about 1/3 full of water and put in a few drops of food coloring. Then, slowly add about the same amount of cooking oil. Now for the top layer-alcohol with a few drops of a different color. After a moment, you should see the two color layers separated by the oil. The really neat thing is you can make the water and alcohol trade places. Slowly turn the container on its side, then upside down (oops - make sure the lid is on tight first!). The alcohol and water are miscible fluids - that it, they mix together easily. So you have to make sure the oil stays between the two layers for this to work. Our liquid sandwich is also a reversible sandwich. Wow!
No discussion about the science of cooking would be complete without mention of yeast. Yeasts are hardy, microscopic, single-cell organisms that can survive in a dry, inactive state for a very long time. But they wake right up when placed in a warm, wet solution and given food in the form of sugar or starch. When exposed to oxygen, yeast cells digest sugars and starches and release carbon dioxide gas and water as waste. In breadmaking, author Tina Seelig tells us in her book
The Epicurean Laboratory that carbon dioxide bubbles trapped in the dough cause the bread to rise. In a hot oven the bubbles expand, causing the dough to rise even more, making the bread light and delicate. Hope you've enjoyed our time in the laboratory, or should I say kitchen, this week. Happy Holidays, and
bon appetit!
