Yeasty Beasties

Abstract

Objective

In this project you will measure the fermentation activity of yeast in different conditions.

Credits

Sara Agee, Ph.D., Science Buddies

Share your story with Science Buddies!

I Did This Project! Please log in and let us know how things went.

Introduction

Yeasts are micro-organisms that are more closely related to a mushroom (they are a single-celled fungi) than to bacteria. Fungi are not green, do not have chlorophyll, and cannot undergo photosynthesis to make their own food. Instead, yeast must get their food from their surrounding environment. Yeasts use sugars (simple carbohydrates) and starches (complex carbohydrates) as food sources.

Yeasts break down these sugar molecules to make energy and release carbon dioxide gas (CO₂) as a result. The carbon dioxide gas is what makes a slice of bread so soft and spongy. The pockets of gas are produced by yeast when the dough is allowed to rise before baking. This is the process of fermentation. Fermentation is also used to make beer, wine, and champagne.

In this experiment you will grow yeast in different conditions to see which conditions will cause the yeast to be most active during fermentation. You will use balloons to trap the CO₂ gasses released by the yeast during fermentation. Then you will submerge the balloons under water and use water displacement to measure the amount of gas in each balloon. Which conditions will cause the formation of the most CO₂ gas and the most active fermentation?

Terms and Concepts

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• yeast
• micro-organism
• fermentation
• carbon dioxide gas (CO₂)
• water displacement

• Are yeasts alive?
• How can the activity of yeast be measured?
• How much gas can yeasts produce?
• What are the best conditions for yeast to ferment?

Bibliography

• This project is based on a classic science demonstration, nicely described by the Exploratorium, a hands-on science museum in San Francisco:
  Exploratorium Staff, 2006. "The Science of Bread: Yeast Air Balloons Activity," The Exploratorium, San Francisco, CA. [accessed July 3, 2006]
  http://exploratorium.edu/cooking/bread/activity-yeast.html
• Here is an interesting twist on the project using different juices as a sugar source, submitted by Cara from Maryland to Zoom Science at PBS Kids:
  Zoom, 2005. "Yeast: Part II," Zoom Science, PBS Kids. [accessed July 3, 2006]
  http://pbskids.org/zoom/activities/sci/yeastpartii.html#results
• Wikipedia contributors, "Yeast," Wikipedia, The Free Encyclopedia [accessed July 3, 2006]
  http://en.wikipedia.org/w/index.php?title=Yeast&oldid=65628541

Materials and Equipment

• 5 packets of dry yeast
• 5 recycled plastic liter bottles
• white table sugar
• salt
• baking soda
• vinegar
• water
• small balloons
• string or clips for tying off balloons
• large, clear, metric liquid measuring cup
• permanent marker

Share your story with Science Buddies!

I Did This Project! Please log in and let us know how things went.

Experimental Procedure

1. First, prepare and label the water bottles for your experiment. Rinse each bottle thoroughly with water and remove any labels. Label each bottle with the permanent marker, using this data table as a guide (all bottles will have yeast):

   Bottle	Condition	Balloon Color	Observations	Water Before (mL)	Water After (mL)	Water Displaced (mL)
   #1	no sugar
   #2	sugar
   #3	sugar + salt
   #4	sugar + baking soda
   #5	sugar + vinegar

2. Add 1 tbsp of sugar to bottles 2–4. Do not add sugar to bottle #1 because it is the negative control. Yeast needs sugar for the process of fermentation, so bottle #1 should stay inactive. Bottle #2 will only have sugar and will be a positive control.
3. Add 1 tbsp of salt to bottle #3. This will increase the salinity, or amount of salt, in the environment. How do you think increasing the salinity will affect fermentation?
4. Add 1 tbsp of baking soda to bottle #4. This will lower the pH of the environment, making the environment more basic. How do you think a basic environment will affect fermentation?
5. Add 1 tbsp of vinegar to bottle #5. This will increase the pH of the environment, making the environment more acidic. How do you think an acidic environment will affect fermentation?
6. Fill each bottle with 300 mL (about 1/3 full) of warm water, replace the lid, and shake thoroughly to dissolve all of the ingredients. Then add a packet of dry yeast to each bottle.
7. Replace the lid and shake gently to mix in the yeast.
8. Remove the lid and stretch a balloon over the opening of each bottle. Choose a different color balloon for each condition and write the color in your data table.
9. Leave the bottles to rest in a warm location for 1 hour.
10. After 1 hour, look at the balloons. Are they the same or different? Write your observations in the data table.
11. Tie a length of string tightly around the base of each balloon to seal the balloon so that any gas inside cannot escape. When the balloon is tightly sealed, remove it from the bottle top, being VERY CAREFUL not to loosen the string or allow any air to escape from the balloon.
12. Now you are ready to measure the amount of gas inside each balloon with a water displacement test. Fill the large measuring cup with enough water to fully submerge the balloon. To be sure that the container is large enough for the balloons, and that you do not fill it with too much water, do a trial run with a balloon you blow up yourself. Practice dunking the balloon without spilling any water out of the measuring tank and without dunking your hand in, too. Then, when you feel ready, dunk each experimental balloon into the water, each time writing the water level before and after into the data table.
13. Subtract the water level before from the water level after to get the volume of gas produced by the yeast.
14. Graph your results for each environmental condition. Under which conditions did the yeast produce the most CO₂ gas? What does that say about the amount of fermentation and activity of the yeast?

Share your story with Science Buddies!

I Did This Project! Please log in and let us know how things went.

Variations

• Another environmental condition that can affect the activity of yeast and the process of fermentation is temperature. Prepare several bottles using the ideal conditions you describe above. Now place each bottle in a different place with a different temperature. After one hour, measure the amount of gas produced and compare.
• In this experiment, you added the same amount of sugar to each bottle because it is what the yeast uses to make CO₂ gas during fermentation. If you add more sugar, will you always get more CO₂ gas? How much more sugar can you add? Is there a limit?
• More advanced students may want to try these Science Buddies projects using yeast:
  • Rise to the Occasion: Investigating Requirements for Yeast Fermentation
  • Yeast Reproduction in Sugar Substitutes
  • An Aerobic Exercise: Yeast Metabolism with and without Aeration

Share your story with Science Buddies!

I Did This Project! Please log in and let us know how things went.

Ask an Expert

Related Links

• Science Fair Project Guide
• Other Ideas Like This
• Microbiology Project Ideas
• My Favorites
• Microorganisms Safety Guide

If you like this project, you might enjoy exploring these related careers:

Microbiologist

Microorganisms (bacteria, viruses, algae, and fungi) are the most common life-forms on Earth. They help us digest nutrients; make foods like yogurt, bread, and olives; and create antibiotics. Some microbes also cause diseases. Microbiologists study the growth, structure, development, and general characteristics of microorganisms to promote health, industry, and a basic understanding of cellular functions. Read more

Biochemical Engineer

A nice cool yogurt is the perfect snack. It comes in a variety of delicious flavors like peach, chocolate, and cherry and contains calcium, vitamins, and minerals that are good for you. Yogurt also contains live cultures that your body needs to maintain good health. How did all of those good things get into your yogurt? The answer is that a biochemical engineer helped to develop a recipe to make that yogurt a perfect snack for you. So many of the products that we use every day, from medicine and fertilizer to packaged foods, result from the hard work of a biochemical engineer. A biochemical engineer takes a recipe that has been formulated by a biologist or a chemist in the laboratory and develops it into a large-scale manufacturing process. Biochemical engineers design the manufacturing equipment that is required to convert raw materials into the products that you have at home, like cold tablets and packaged foods. If you are interested in applying your problem-solving skills to improving human lives, then you should definitely investigate this career. Read more

Food Scientist or Technologist

There is a fraction of the world's population that doesn't have enough to eat or doesn't have access to food that is nutritionally rich. Food scientists or technologists work to find new sources of food that have the right nutrition levels and that are safe for human consumption. In fact, our nation's food supply depends on food scientists and technologists that test and develop foods that meet and exceed government food safety standards. If you are interested in combining biology, chemistry, and the knowledge that you are helping people, then a career as a food scientist or technologist could be a great choice for you! Read more

Biological Technician

What do the sequencing of the human genome, the annual production of millions of units of life-saving vaccines, and the creation of new drought-tolerant rice varieties have in common? They were all accomplished through the hard work of biological technicians. Scientists may come up with the overarching plans, but the day-to-day labor behind biotech advances is often the work of skilled biological technicians. Read more