Use yeast to blow up a balloon!

Author: Maddie Van Beek 

You may have heard of yeast, but today you will actually learn what this substance is and what it does.

​Have you ever seen a little square packet labeled yeast in your cupboard at home or on a shelf at the grocery store and wondered it was used for? 

Inside the packet, you’ll see a substance that looks something like this:

Granulated dried yeast

Some yeast is packaged like the picture above. Rather than packets of dried yeast granules, this is compressed fresh yeast.

Pretty boring, right? Why would these little brown granules called yeast be so important for making bread? 

Did you know that yeast is not only crucial to bread rising, it is actually ALIVE?!

The scientific name for this tiny little organism is Saccharomyces cerevisiae, but they should just call it, “sugar-eater.” Yeast feeds on the sugar in the bread dough and converts it into carbon dioxide. The carbon dioxide creates little bubbles in the dough, which is what causes the bread to rise and creates a nice spongy texture rather than a hard flatbread. Your PB&J sandwiches would have never been the same without the discovery of yeast! 

This could not happen without yeast:

Here is a close-up of what yeast organisms look like:

Yeast under a microscope

How does yeast work?

CHECK FOR UNDERSTANDING:

• What kind of organism is yeast? 
• Where might you find yeast?
• What does yeast do? (What is its job?)
• What is yeast used for? Think of a few different examples. 

Learn more about bread-related science and the research that is going into yeast today!

Remember when we blew up a bag with baking soda and vinegar? Today, we are going to try something similar with yeast!

Check out this video for a demonstration of what you will do!

CHECK FOR UNDERSTANDING:

• Based on your experience last week, what do you think is happening as the yeast blows up the balloon? 
• How is the balloon being blown up?
• What is the yeast doing to produce gas?
• What kind of gas is being produced? 

Now that you've seen a demonstration of what yeast can do, try it out yourself! 

YOU WILL NEED:

• Baker’s yeast
• Warm water
• Water bottle
• Balloon
• Sugar
• Funnel

HERE’S WHAT TO DO:

1. First, you need to stretch out your balloon. Blow it up a few times to loosen it up. 
2. Next, measure one cup of very warm water.
3. Stir in one packet of yeast and two tablespoons of sugar. Keep stirring until the mixture is dissolved.
4. Place the funnel at the mouth of the water bottle, and pour the sugar-water-yeast substance into it. 
5. Stretch the mouth of the balloon over the mouth of the water bottle.
6. Wait, and record your observations. This may take a while, so you might want to check back every 15-20 minutes. 
7. What does the sugar-water-yeast substance look like at first? What happens over time? What happens to the balloon? How long does this take? 

Extension 1:

Test out how different water temperatures might affect the yeast! 




YOU WILL NEED:

• Thermometer
• Ruler/tape measure

PREDICT: How might temperature affect the yeast? 




HERE’S WHAT TO DO:

1. Follow the instructions above, except use a different temperature of water. Try using very hot water, lukewarm water, cold water, etc. You will need a thermometer in order to accurately track how temperature affects the production of carbon dioxide. 
2. Use a ruler to measure how large the balloon gets. Measure from the mouth of the water bottle to the top of the balloon each time.  
3. Repeat the experiment as many times as you would like with different temperatures of water and record your observations each time. 
4. Create a graph to demonstrate the relationship between water temperature and carbon dioxide production. Your X-axis would be temperature and your Y-axis would be inches grown. For Excel instructions, check out our recent blog on heart health. (You would be creating a graph of inches  grown as a function of water temperature). 

Extension 2:

Test out how different amounts of sugar might affect the yeast!

Does more sugar equal more carbon dioxide? Try it out! 

PREDICT: How might the amount of sugar affect the yeast? Will more sugar make the balloon grow bigger? 


HERE'S WHAT TO DO: 

1. Follow the instructions in the original experiment, except use a different amount of sugar. Try using one tablespoon, 1/2 teaspoon, 1/4 cup, etc. 
2. Use the ruler to measure how large the balloon gets. 
3. Create a graph to demonstrate the relationship between the amount of sugar used and carbon dioxide production. Your X-axis would be the amount of sugar used and your Y-axis would be inches grown. For Excel instructions, check out our recent blog on heart health. (You would be creating a graph of inches grown as a function of the amount of sugar used). 

References: 

http://phys.org/news/2013-11-bread-beer-national-yeast-cultures.html

http://www.scientificamerican.com/article/watch-yeast-live-breathe/

https://www.exploratorium.edu/cooking/bread/activity-yeast.html

http://science.howstuffworks.com/life/fungi/yeast-info.htm

http://en.wikipedia.org/wiki/Yeast#Baking

Image and video credits, in order of appearance
​
Hellahulla, 2007. Compressed fresh yeast. Uploaded from Wikimedia Commons on 9/11/2016.
https://upload.wikimedia.org/wikipedia/commons/thumb/e/e9/Compressed_fresh_yeast_-_1.jpg/1024px-Compressed_fresh_yeast_-_1.jpg File used under GNU Free Documentation License. No changes were made. 

Ranveig, 2005. Dry yeast. 
​https://upload.wikimedia.org/wikipedia/commons/thumb/9/90/Dry_yeast.jpg/800px-Dry_yeast.jpg File in the Public Domain. No changes were made. 

Reynaud, 2012. Bread rising (Timelapse). Uploaded from YouTube on 9/11/2016. 
​https://youtu.be/0z8hrRXQuHY

Masur, 2009. S cerevisiae under DIC microscopy. Uploaded from Wikimedia Commons on 9/11/2016. https://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/S_cerevisiae_under_DIC_microscopy.jpg/800px-S_cerevisiae_under_DIC_microscopy.jpg File in the Public Domain. No changes were made. 

Timstar Laboratory Suppliers, 2013. Demonstration of keystage 3 biology experiment - Blow up a balloon with yeast. Uploaded from YouTube on 9/11/2016. ​https://youtu.be/wTmcUvQhU-o