You’ll need

  • Ziplock bags OR small glass jars
  • Measuring spoons
  • Dried, instant brewer’s yeast
  • Sugar
  • Warm water
  • Balloons and rubber bands

What to do

  1. Add 1 tablespoon of sugar and 1 teaspoon of dried yeast to the ziplock bag or jar.
  2. Pour warm water into the bag or jar until it is half full.
  3. Squeeze the extra air out of the ziplock bag. If you are using a jar, cover it with a balloon and seal with a rubber band.
  4. Leave the yeast mixture in a warm area and check it every 15 minutes.
  5. If you are using a ziplock bag, you might need to open it and let some of the gas out.
  6. If you are using a jar and a balloon, measure the diameter of the balloon at its widest point.

Questions to ask

What happened when you added the warm water to the yeast and sugar?

Try changing some parts of the experiment and see what happens to the amount of gas made:

  • Add 1 teaspoon of salt to one container instead of sugar.
  • Don’t add sugar to one container.
  • Don’t add yeast to one container.
  • Put some yeast in the freezer for 1 hour before adding it to a container.
  • Put some yeast in the microwave and cook it for 10 seconds before adding it to a container.
  • Use iced water with the yeast and sugar.

Feel like investigating some more? Try these:

  • About how much yeast, sugar and water do you need to fill one ziplock bag with gas?
  • Instead of sugar, try using different foods like honey, fruit juice or vinegar. What happens to your mixture?
  • What happens if you add more yeast to the mixture? What about more sugar?
  • Do you notice a difference in the amount of gas produced if you keep the mixture in a cool place?
  • What happens if you take some of the yeast mixture and add it to another container that contains sugar and water?

What's happening

When you look at dried yeast, it doesn’t look as though it’s alive. But looks can be deceiving. Yeast is a type of fungus (mushrooms are also fungi).

Some living things, like dried yeast, have a dormant stage. Dormant means it is not active or growing. But when you add warm water and sugar, the yeast starts to grow. It produces carbon dioxide, which is the bubbles you can see in the yeast mixture.

Yeast doesn’t like the temperature too hot or too cold. It also likes to have lots of the right food so it can grow. Yeast is just like us!

Did you know

Humans have used brewer’s yeast for making bread for about 5,000 years. When making bread dough, yeast is used to raise or expand the dough before it is baked. The yeast gives off bubbles of carbon dioxide, which makes the bread light and airy.

Brewer’s yeast is also used to make alcohols like beer and wine.