What You Need:
- 3 little pouches, or 3 teaspoons, of dry yeast
- Magnifying glass
- 3 plastic zip-top bags
- ¼ cup of lukewarm water
- 2 teaspoons sugar
What You Do:
- Lay a sheet of plain dark paper onto a clean, well-lit table surface. Then, pour out the contents of one yeast pouch, dry, and invite your child to take a good look with a magnifying glass. What does she see? Note together how the yeast doesn’t move or seem to breathe—indeed, it doesn’t seem alive, does it? When you’re done, carefully sweep the yeast into one of the plastic bags and put it aside.
- Now tell your child it’s time for some experimenting. Pour out the contents of another yeast packet onto the dark paper, and mix it with one teaspoon of dry sugar. One way we can tell if things are alive is if they move together, or even absorb one another. Grab the magnifying glass and take a look again. See anything alive? (Probably not!) When you and your child are done taking a look, pour the dry sugar and yeast into the second plastic bag.
- Take the last packet and pour it straight into the last plastic bag. Add the second teaspoon of sugar, and then (after making sure your bag has no holes), pour in the lukewarm water. Zip the bag securely shut.
- Put all three bags in sunny window for approximately 20 minutes, and then check them out: the first two bags will show no change in the yeast, but that third bag will be…well, transformed. The bag should be puffy, and the yeast will have mostly dissolved. Try pouring a little of the solution into a clear bowl placed over the dark sheet paper or another dark surface, and have a look with the magnifying glass.
Yeast really is, in fact, alive. It’s a one-celled member of the fungus family, and when you add water to it and give it a little sugar for food, the organism "burps" and releases carbon dioxide—the gas that makes the bag puff out and makes sodas fizzy and bread fluffy.
If you want to make the most of this experiment, pour the rest of dry yeast into the wet yeast mixture, let it sit just a few minutes longer, and then mix the whole thing into a nice big batch of bread dough. Bake it up and enjoy. If there was ever any doubt before, this is an activity that will remind your child that science is simply delicious!