The Good, the Bad, and the Tasty

Not all bacteria are bad. They do interesting things to foods: Milk becomes cheese, a flour and water paste rises and becomes bread when baked. Many of these changes are produced by one-celled plants called yeasts. Yeasts belong to a group called fungi. Unlike green plants, they don't contain a food factory. No chlorophyll. No photosynthesis. They get their food from their surroundings.

What foods do yeasts eat? What do they produce as wastes? Good questions. Ready?

What You Need:

• Adult help.
• Water.
• A package of dry yeast.
• A measuring cup.
• 3 small glasses.
• A candy thermometer.
• A large pot.
• 3 spoons.
• Measuring spoons.
• Sugar, corn syrup, and cornstarch.

What You Need To Do:

Dissolve the yeast in 1/2 cup of 90 degrees F water. Divide this mixture equally into the glasses. Make a warm water bath in the large pot with 90 degree F water. Put in enough water so the glasses can sit in it without water spilling into them. Put 1 tablespoon of sugar in the first glass, 1 tablespoon of corn syrup in the second, and 1 tablespoon of cornstarch in the third. Stir each glass with a different spoon. Put the glasses in the warm water bath and look for bubbles.

Which glass produces bubbles first? Which makes the biggest bubbles?

What Do You See?

Yeasts, like all living organisms, have to eat. They eat glucose, the product of the plant factory. Corn syrup comes from corn plants (no kidding!), so it contains glucose. When yeasts munch on glucose (what people in the know call fermentation), they produce by-products the yeasts consider wastes. However, we find these 'wastes' helpful. One is carbon dioxide. It's the bubbles given off first by the corn syrup set-up. The other two produce carbon dioxide more slowly. Reason? Starch and sugar are more complicated molecules and take longer to break down.

Who cares? Unless you like your bread paper thin (and tough as shoe leather), you care. The carbon dioxide gas makes bread rise. Warm, airy bread from the oven . . . all because the Creator designed some wee plants for a purpose.