While you are enjoying your hotdog or hamburger this summer, take a closer look at the bun. Do you notice tiny holes or air spaces in the bread? Where did these holes come from? You might not believe it, but the holes were formed by a fungus that the baker intentionally added to the bread dough. Complete the activity below to learn why fungi are so important for fluffy bread.
Materials: bakers yeast, 1 cup of very warm water (105° F–115° F), sugar, measuring spoons, large balloon, small water bottle, funnel (optional)
Stretch out the balloon by blowing it up and then releasing the air. Set the balloon aside for now; you will need it again for step five. Add two tablespoons of sugar to the cup of warm water and stir until the sugar dissolves.Now add one tablespoon of yeast to the cup and stir briefly.Carefully pour the contents of the cup into the water bottle. You may want to use a funnel to prevent spills.Stretch the balloon over the opening of the bottle.Watch the balloon closely. Be patient – it may take a few minutes before you see any changes.
Now Try This:
Try the same experiment using hotter and colder water. Does the temperature of the water affect how long it takes for the balloon to inflate? What if you substituted juice or soda for the sugar water solution? Would you get the same result? Try it and find out.
What’s Going On?
Yeast is a type of single-celled fungus that is used in baking to make bread rise. Yeast does this by feeding on sugars in the flour and releasing carbon dioxide gas as waste. The carbon dioxide from the yeast makes thousands of bubbles in the dough. These air bubbles are what give the loaf of bread its fluffy texture. The process of breaking down sugar molecules into alcohol and carbon dioxide is called fermentation. This same process occurred inside the water bottle. The yeast began to feed on the sugar in the water, releasing carbon dioxide gas. The carbon dioxide gas caused the balloon to fill up.
There are many different types of yeasts, and each has a particular food source. Some yeast break down fruit into wine, while others convert wood and corn into ethanol. Bakers yeast (Saccharomyces cerevisiae) is the type of yeast used in baking. It has special enzymes that allow it to break down sugars.
Debbie De Roma is the Education Manager at the Reuben H. Fleet Science Center.