yeast and sugar balloon experiment lab report

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Blowing Up Balloons Respiration Style

June 18, 2012 By Emma Vanstone 5 Comments

We’ve talked about respiration before when we made bread and used yeast to make the dough rise. Blowing up a balloon with yeast is another very easy experiment to demonstrate respiration in action and is quicker than making bread if you are short of time.

What is respiration?

Respiration is a chemical reaction which occurs in animal and plant cells. It releases energy from glucose. Aerobic respiration needs oxygen, but anaerobic respiration doesn’t need oxygen.

Anaerobic respiration produces less energy than aerobic respiration. It occurs in humans when not enough oxygen reaches muscle cells ( for example, during hard exercise ). Bacteria and other microorganisms can also use anaerobic respiration, and yeast actually carry out an anaerobic process called fermentation .

Respiration occurs in the mitochondria of cells. You can find out more about mitochondria by making a model of a cell .

Blow up a balloon with yeast

A small clear drinks bottle

A packet of dried yeast

1 teaspoon of sugar

Instructions

1. Blow the balloon up a few times to give it some stretch. This just makes it easier for the experiment to work.

2. Fill the small bottle about 3cm full of warm water.

3. Add the yeast and 1 teaspoon of sugar.

4. Place the balloon over the open top so no air can escape.

5 Over the next half an hour, watch what happens. (Obviously, do other stuff and come back, it may be a little boring to actually watch it for half an hour!)

Yeast and Respiration

Yeast is a living organism. In order for it to survive, it needs to make energy. In its dried form, the yeast is dormant, but as soon as you provide it with warmth, water and sugar (its food), it ‘wakens’ and becomes active. The yeast uses the sugar (glucose) and oxygen from the bottle to make water, energy and carbon dioxide. Carbon dioxide is a gas, and this is what you see filling the balloon.

Remember, yeast can respire anaerobically when there’s not enough oxygen for aerobic respiration.

Fermentation

Glucose -> ethanol and carbon dioxide + energy

Aerobic Respiration Equation

Glucose + Oxygen –> Carbon Dioxide + Water + energy

The image is taken from Snackable Science which contains SEVENTY fun edible experiments and investigations!

Science concepts

Respiration

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Last Updated on May 3, 2023 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

Reader Interactions

June 18, 2012 at 3:04 pm

Oooh I like this one a lot! I am storing them all up for rainy days but I’ll get to this one quite quickly!

June 18, 2012 at 6:32 pm

What a cool project! Do the balloons float, then, like helium?

June 21, 2012 at 3:21 am

That’s so cool! We love everything science! My kids will love this!

June 25, 2012 at 8:14 pm

Brilliant experiment!!!! The kids will love it!

Thanks for sharing on Kids Get Crafty!

Maggy & Alissa

March 31, 2013 at 9:18 am

all the experiments simple and kids could easily understand the concepts behind it.

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Inflate a Balloon with Yeast Experiment

Did you know that you can inflate a balloon WITHOUT blowing air into it? It’s true.

In this simple experiment , young scientists use yeast to magically inflate a balloon. How cool is that?!

Check out the simple step-by-step below and then snag our 30 Science Experiments that are kid-approved!

Getting Ready

We headed into the kitchen to grab all of our supplies for this science experiment:

• Clear plastic or glass bottle with a narrow neck (a water bottle or soda bottle work great)
• 2 Tablespoons dry yeast
• 1 Tablespoon sugar
• 2-3 Tablespoons lukewarm water
• Party balloon
• Bowl or mug full of lukewarm water

Inflating a balloon with yeast is a wonderful experiment to do with preschool and kindergarten aged children because all of the materials are nontoxic. It’s nice when the kids can help measure out ingredients without worrying about what they are touching.

My kids helped me measure the yeast, sugar, and warm water into a cup.

They stirred the ingredients and then used a funnel to pour the brown mixture into the bottle. We added a little bit more water to help the yeast mixture get through the neck of the funnel.

We quickly stretched a balloon over the mouth of the bottle.

After placing the bottle into a mug full of warm water, we sat back to observe.

Inflate a Balloon with Yeast

Almost immediately, we observed bubbles in the yeast mixture.

I explained to the kids that yeast is a microscopic fungus that converts sugar into carbon dioxide.

The bubbles they saw were tiny bubbles of carbon dioxide gas that the yeast was producing as it “ate” the sugar.

For yeast to be active, it needs to be warm and moist. That’s why we added lukewarm water and placed the bottle in more warm water.

We set our bottle of yeast on the table and watched it while we ate lunch and read books.

We checked in with our science experiment every 10 minutes or so to observe any changes. Every time we looked, we noticed that the balloon was getting bigger and bigger on top of the bottle! Why?

As the yeast continued to react, it converted more and more sugar into carbon dioxide gas.

This gas was trapped in the balloon, making it inflate as if by magic!

It took about an hour for our balloon to reach its maximum size.

The yeast bubbled up into the bottle quite a bit before it stopped reacting and shrank down again. Simple science at its best.

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Yeast-Air Balloons

The purpose of any leavener is to produce the gas that makes bread rise. Yeast does this by feeding on the sugars in flour, and expelling carbon dioxide in the process.

While there are about 160 known species of yeast, Saccharomyces cerevisiae, commonly known as baker's yeast, is the one most often used in the kitchen. Yeast is tiny: Just one gram holds about 25 billion cells. That amount of fungi can churn out a significant amount of carbon dioxide, provided it has the simple sugars it uses as food. Fortunately, yeast can use its own enzymes to break down more complex sugars—like the granulated sugar in the activity below—into a form that it can consume.

Make a yeast-air balloon to get a better idea of what yeast can do.

Did You Know?

What do i need.

1 packet of active dry yeast

1 cup very warm water (105° F-115° F)

2 tablespoons sugar

a large rubber balloon

a small (1-pint to 1-liter) empty water bottle

Kids, please don t try this at home without the help of an adult.

What do I do

Stretch out the balloon by blowing it up repeatedly, and then lay it aside.

Add the packet of yeast and the sugar to the cup of warm water and stir.

Once the yeast and sugar have dissolved, pour the mixture into the bottle. You ll notice the water bubbling as the yeast produces carbon dioxide.

Attach the balloon to the mouth of the bottle, and set both aside.

Step 5: After several minutes, you ll notice the balloon standing upright. If you don t see anything happen, keep waiting. Eventually, the balloon will inflate.

What's going on.

As the yeast feeds on the sugar, it produces carbon dioxide. With no place to go but up, this gas slowly fills the balloon.

A very similar process happens as bread rises. Carbon dioxide from yeast fills thousands of balloonlike bubbles in the dough. Once the bread has baked, this is what gives the loaf its airy texture.

What Else Can I Try?

Try the same experiment, but this time use about a tablespoon of baking powder instead of yeast, and leave out the sugar. What differences do you notice? Which leavener takes longer to fill up the balloon?

Also, try the same experiment using hotter and colder water. Use a thermometer to measure the temperature of the water. At what temperature is the yeast most active? At what temperatures is it unable to blow up the balloon?

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Blow up a balloon with yeast, you will need.

A packet of yeast (available in the grocery store) A small, clean, clear, plastic soda bottle (16 oz. or smaller) 1 teaspoon of sugar Some warm water A small balloon

1. Fill the bottle up with about one inch of warm water. ( When yeast is cold or dry the micro organisms are resting.) 2. Add all of the yeast packet and gently swirl the bottle a few seconds. (As the yeast dissolves, it becomes active – it comes to life! Don’t bother looking for movement, yeast is a microscopic fungus organism.) 3. Add the sugar and swirl it around some more. Like people, yeast needs energy (food) to be active, so we will give it sugar. Now the yeast is “eating!”

4. Blow up the balloon a few times to stretch it out then place the neck of the balloon over the neck of the bottle. 5. Let the bottle sit in a warm place for about 20 minutes If all goes well the balloon will begin to inflate!

How does it work?

As the yeast eats the sugar, it releases a gas called carbon dioxide. The gas fills the bottle and then fills the balloon as more gas is created. We all know that there are “holes” in bread, but how are they made? The answer sounds a little like the plot of a horror movie. Most breads are made using YEAST. Believe it or not, yeast is actually living microorganisms! When bread is made, the yeast becomes spread out in flour. Each bit of yeast makes tiny gas bubbles and that puts millions of bubbles (holes) in our bread before it gets baked. Naturalist’s note – The yeast used in this experiment are the related species and strains of Saccharomyces cervisiae. (I’m sure you were wondering about that.) Anyway, when the bread gets baked in the oven, the yeast dies and leaves all those bubbles (holes) in the bread. Yum.

MAKE IT AN EXPERIMENT

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Does room temperature affect how much gas is created by the yeast? 2. Does the size of the container affect how much gas is created? 3. What water/room temperature helps the yeast create the most gas? 4. What “yeast food” helps the yeast create the most gas? (try sugar, syrup, honey, etc.)

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Yeast and Sugar Science Fair Project

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In this Yeast and Sugar Science Fair Project, we’ll watch yeast feed on sugar to fill a balloon with air. A fun science project for kids that’s with household, everyday materials.

Our Inspiration

I’ve been baking bread just about every day for the past three weeks (nothing too crazy since it’s all done in the bread maker), but last week my 3.5 year old and I got into a discussion about the properties of yeast.

We like to tinker and  experiment — big surprise, I know — and decided to see what would happen if we mixed yeast with warm water.

My preschooler took this job very seriously, poured the water into a bowl, added a couple teaspoons of yeast, and waited a few patient minutes before she said, “it makes a brownish color.” True, and to make it bubble like it does in bread, we needed to activate it with sugar.

What’s so great about an experiment like this is that it’s easy to do with household materials, and it’s ripe for authentic child-generated questions and observations. When I asked what she thought would happen if we added sugar to the yeast she said, “I don’t know! Let’s mix them and find out!.”

Supplies: Yeast and Sugar Science Fair Project

• Sugar, 2 tablespoons
• Active Dry Yeast, 1 packet or 2 1/4 tablespoons
• Warm water (105-115 degrees F, 40.5-46 degrees C)
• Mixing bowl + funnel
• Bottle that you can fit a balloon over

Mix the yeast and sugar into the warm water and stir. I noticed that N was sniffing the concoction and asked her what it smelled like. She said “poop.” I could see what she was saying. Consider yourself warned.

Once it all dissolves, pour the mixture into the bottle and cover the bottle with the balloon.

After a few minutes you’ll be amazed by something like this!

Will it blow off the bottle?

N wanted to feel it as it filled with air. She noticed the balloon was getting bigger and wanted to know how big it would get, wondering out loud, “will it fill up all the way and blow off the bottle?”

Good question!

My handy-dandy ship captain sister (no joke — that’s her job!) was visiting, and put herself right to work as chief measurer.

Move it to a safe spot

Once the bottle filled up completely, we moved the whole yeast sugar experriment to the sink. The bubbles were slow-moving, and there was nothing to worry ourselves with, but N enjoyed pulling the balloon off and watching the foam slowly pour over the bottle’s top.

Ideas for Extending this Experiment

As we went through the process, I thought of a few fun extensions for older kids or those who want to take this further. You could play around with food coloring/liquid watercolors, have a few bottles going at once and compare the results of different sugar:yeast ratios, or compare the results of different water temperatures.

I found my recipe at The Exploratorium’s Science of Cooking series, where we also learned that as the yeast eats the sugar it makes carbon dioxide, which is essentially the same process that yeast goes through in our bread dough.

Mmmmm. I’m off to eat some whole wheat cranberry walnut oat bread. Toasted. With butter and Maldon salt. How do you like your bread? And have you played around with yeast concoctions?

More Science Experiments for Kids

If you enjoyed this project, you’ll love this article:  Science Fair Project Ideas .

What a great idea!!

Thanks, Deborah 🙂

thank you soooooooooooooooooooooooooooo much for this info

I used to bake a lot of bread with my boys when they were younger (pre-celiac diagnosis) and they always loved my scientific explanation of why the bread rises: the yeast eats the sugar and farts. 🙂 That’s what all the bubbles are, of course!

Yep, farts would be another not-so-pretty way to describe this process. Between that and my daughter’s description, I’m not sure if anyone will want to try this themselves 😉

we love yeast! my son thinks of yeast as little pets. here is our experiment we did a few months ago. it seems to come up ever year or so. great post!

http://mamascouts.blogspot.com/2011/09/science-experimentwake-up-yeast.html

Thanks for sharing your yeast experiments, Amy! I love them, and we have to try this with maple syrup next time (if I can convince my MS-adoring family to part with it first!).

way cool! you know I like to tinker as well with my girls – this will be something we can easily do at home.

I pinned this! 🙂 thanks for sharing!

Thanks for pinning it, Bern 🙂 And yes, I can totally imagine your two little scientists going crazy over this one!

This is the best blog for experiments! Thanks for sharing all your great ideas.  Linking up to it in a science for preschoolers post. 

Hi Kristin, Thank you soooooo much for the kind words about Tinkerlab. And thanks for sharing us with your readers….feel free to send me a link if you’d like and I’ll share it on Facebook.

This is so fun! We did this today and the kids loved it. Thank you!

awesome, lindsie! i’m thrilled to hear it was successful. thanks for taking time to give me this update.

Hmmm…sugar, yeast and water…also known as Kilju or sugar wine! https://en.wikipedia.org/wiki/Kilju

As well as CO2, yeast and sugar also produces Ethanol (alcohol). Probably best not to teach the kids that part though!

That’s funny, Chris. I’m sure that my 4-year old won’t be least bit interested in sugar wine!

Point taken. Out of interest, did you ever find out what made the “poop” smell? In theory it should just produce CO2 which doesn’t smell.

could i add flour to the mixture. would it have the same effect ?

it’s nice

moooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

why soooooooo many o’s sara

What quantity of water did you use? I’m doing an adaptation of this for my science assignment

Miguel Cabrera

What were the measurements for each balloon

Thanks for this great post. We did this today while baking bread. My boys loved measuring the baloons often and seeing what would happen.

[…] is a safe activity for preschoolers and toddlers because you are using edible materials. Moreover, kids will see, touch, and smell while observing, […]

Thanks Nice Experiment

I don’t get it, it does not have a video!

[…] Blow Balloon With Yeast Experiment […]

Is this supposed to be 2 1/4 TEASPOONS or TABLESPOONS. Your instructions say one packet of yeast (which is 2/4 teaspoons) but you wrote 2 1/4 tablespoons. Thanks for any clarification you can provide

* my comment should read that one packet of yeast is 2 1/4 teaspoons

Comments are closed.

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Yeast-Inflated Balloons

Activity length, 30-40 mins., chemical reactions fungi, bacteria & viruses states of matter, activity type, exploration.

Students use yeast to explore CO 2  production by living organisms.

This is an excellent opportunity for students to design their own experiments to determine which variables affect the yeast’s ability to produce CO 2 .

Yeast is a fungal microorganism that feeds on sugar and produces carbon dioxide (CO 2 ) plus ethanol. As the yeast feeds on the sugar, it produces carbon dioxide gas. This process is known as fermentation. The trapped CO 2  accumulates inside the balloon, slowly inflating it.

A very similar process happens as bread rises. Carbon dioxide from yeast fills thousands of balloon-like bubbles in the dough. This is what gives baked bread its airy texture.

Since yeast also produces alcohol as it feeds, it is an important ingredient in beer & wine production.

Determine variables used in an experiment of their own design.

Create a hypothesis

Describe one of the by products of respiration.

Describe the properties of gases.

Per Pair of Students: 1 tbsp (15 ml) active dry yeast (not fast-acting) 1 teaspoon (5 ml) sugar 1 cup (250 ml) very warm water (41–46°C or 105–115°F ) funnel balloon measuring tape (flexible kind) spot near a heat source (like a radiator or a sunny window)

Key Questions

• What special characteristic of yeast made the balloon inflate?
• Why was the sugar added?
• Why did we need to put the balloon in a warm place?
• Would you get the same results if the balloon was untied?
• Measure the length and circumference of your balloon. Record the results.

• Pour 1 tablespoon of yeast and 1 teaspoon of sugar into the balloon using the funnel.
• Slowly add the cup of very warm water.
• Remove the funnel from the balloon and tie it closed.
• Place the balloon in a warm place.
• Measure the length and circumference of the balloon every 15 minutes for an hour. Record the results.

​Teacher Tip: Try fast-acting yeast if you need the yeast to work within a shorter period of time.

• Design an experiment to explore one of the following questions:
• Which sugar/food combination helps the yeast produce the most gas?
• Try different foods for the yeast to ferment, e.g. brown sugar, syrup, honey, candy, salt. At what temperature is the yeast most active? At what temperatures is it unable to blow up the balloon?
• Try varying the water temperature, using a thermometer to measure the temperature of the water.

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• Fermentation, or how to blow up a balloon with yeast!

image bt Ingenza Ltd

If you have ever baked bread, you probably have encountered yeast and used it to make the dough rise. But how does it work? The yeast you can buy in a shop is called Saccharomyces cerevisiae , or just baker’s yeast. Yeasts break down sugars and produce alcohol, which is used in alcoholic beverages, and carbon dioxide, which is a gas that makes bread dough rise.

You can see the fermentation process in a very easy way at home, by mixing some active dry yeast, sugar and warm water in an empty bottle and fit a balloon over the bottle top. Watch the balloon blow up magically!

Here is how you can do it: 

• Packet of yeast
• Empty Water Bottle
• Funnel 

Use the funnel  to put a couple of spoonfuls of sugar in an empty water bottle. 

Fill half of the bottle with warm water.

Add a package of yeast. Yeast is activated when it gets wet. So, put the top on and shake the bottle. Open the bottle again and place the ballon over the bottle opening. 

Finally you wait for the magic to happen. It will take more than an hour to get the balloon really good and inflated.

But how does this work? Yeast  is a microscopic fungus. As the yeast eats the sugar, it releases a gas called carbon dioxide. The gas fills the bottle and then fills the balloon as more gas is created.

Tips for the experiment and food for thought:

• Try to use clear bottles, so you can see the liquid bubbling!
• Try repeating the experiment with cold water. Or, putting the bottles in a warm place like a sunny window sill. Does the temperature influence the activity of the yeast?
• Try adding different amounts of sugar (or no sugar!) to the mixture. Which bottles grow the balloon most?
• Can yeast use other sugars than sucrose (which is the sugar in household sugar)? How about using some fruit juice (with a lot of fructose) or milk (with lactose)?
• When the balloons are all blown up, don’t forget to take a whiff before throwing it away! What does the smell remind you of? How do different bottles differ in their smell?

If you want to see a video with the experiment click here . 

The same process happens when we are making bread. Check this video to find out more.

By Daniel Sachs

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Yeast Fermentation Experiment

Fermentation is a fascinating process that kids can easily explore through a simple experiment using yeast and sugar. This hands-on activity teaches students about fermentation and introduces them to the scientific method, data collection, and analysis.

Investigate how different types of sugar (white, brown, and honey) affect the rate of yeast fermentation by measuring the amount of carbon dioxide (CO₂) produced.

Example Hypothesis: If yeast is added to different types of sugar, then the type of sugar will affect the amount of carbon dioxide produced, with white sugar producing more CO₂ than the others.

💡 Learn more about using the scientific method [here] and choosing variables .

Watch the Video:

• Active dry yeast
• White sugar
• Brown sugar
• Measuring spoons and measuring cups
• Small bottles or test tubes
• Rubber bands
• Ruler or measuring tape
• Notebook and pen for recording data ( grab free journal sheets here )
• Printable Experiment Page (see below)

Instructions:

STEP 1. Prepare a yeast solution by dissolving a packet of active dry yeast in warm water according to the package instructions.

STEP 2. Label 3 bottles and add 1 tablespoon of white sugar to the “White Sugar” bottle. Add 1 tablespoon of brown sugar to the “Brown Sugar” bottle. Measure 1 tablespoon of honey and add it to the “Honey” bottle.

STEP 3. Measure and pour an equal amount of the yeast solution into each bottle, ensuring the yeast is well mixed with the sugar.

STEP 4. Quickly stretch a balloon over the mouth of each bottle. Secure the balloons with rubber bands if needed. Ensure the balloons are sealed tightly to prevent CO₂ from escaping.

STEP 5. Place the bottles in a warm, consistent environment to promote fermentation.

STEP 6. Observe and record the size of the balloons at regular intervals (e.g., every 15 minutes) for 1-2 hours. Use a ruler or measuring tape to measure the circumference of each balloon.

TIP: Note the time it takes for the balloons to start inflating and the differences in balloon size over time for each type of sugar.

STEP 7: Analyze the data by comparing the amount of CO₂ produced (balloon size) for each type of sugar. Create a graph showing the balloon size over time for each sugar type.

STEP 8. Determine which sugar type resulted in the most and least CO₂ production. Discuss possible reasons for the differences, considering what each sugar is made of. Think about whether the results support or disprove the hypothesis. Can you come up with further experiments or variations to explore other factors affecting yeast fermentation?

Free Printable Yeast and Sugar Experiment Project

Grab the free fermentation experiment worksheet here. Join our STEM club for a printable version of the video!

The Science Behind Yeast Fermentation

For Our Younger Scientists: Yeast is a type of fungus that feeds on sugars. When you mix yeast with sugar and water, it starts to eat the sugar and convert it into alcohol and carbon dioxide gas. The gas gets trapped in the balloon, causing it to inflate. This shows that fermentation is happening!

Yeast fermentation is a biological process where yeast converts sugars into alcohol and carbon dioxide (CO₂) in the absence of oxygen. This process is used in baking, brewing, wine making and biofuel production. How much fermentation occurs can vary depending on the type of sugar used.

Yeast contains enzymes that break down sugar molecules through a series of chemical reactions . Here’s how it works:

Enzymes are molecules, usually proteins, that act as catalysts to speed up chemical reactions within living organisms.

First the yeast is mixed with warm water, and it becomes activated. The warm environment “wakes up” the yeast cells, preparing them to consume sugars.

Yeast cells produce enzymes that break down sugar molecules (sucrose, glucose, and fructose) into simpler molecules. This process is called glycolysis. During glycolysis, sugar molecules are converted into pyruvate, releasing a small amount of energy.

In the absence of oxygen (anaerobic conditions), yeast cells convert pyruvate into ethanol (alcohol) and carbon dioxide gas (CO₂). The carbon dioxide produced during fermentation is what inflates the balloons in the experiment.

Different Sugars & Fermentation

Different sugars can affect the rate of fermentation. This is how:

• White Sugar (Sucrose): Composed of glucose and fructose and is easily broken down by yeast, leading to efficient CO₂ production.
• Brown Sugar: Contains sucrose along with molasses, which includes minerals and additional nutrients. May result in a slightly different fermentation rate due to its composition.
• Honey: Contains a mixture of glucose, fructose, and other components. The additional components can influence the fermentation process, potentially leading to different CO₂ production rates compared to pure sucrose.

The amount of CO₂ produced depends on how easily the yeast can break down the sugar molecules and convert them into ethanol and CO₂. Sugars that are more readily broken down by yeast will typically produce more CO₂ faster.

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The fermentation of sugars using yeast: A discovery experiment

Charles Pepin (student) and Charles Marzzacco (retired), Melbourne, FL

Introduction

Enzyme catalysis 1  is an important topic which is often neglected in introductory chemistry courses. In this paper, we present a simple experiment involving the yeast-catalyzed fermentation of sugars. The experiment is easy to carry out, does not require expensive equipment and is suitable for introductory chemistry courses.

The sugars used in this study are sucrose and lactose (disaccharides), and glucose, fructose and galactose (monosaccharides). Lactose, glucose and fructose were obtained from a health food store and the galactose from Carolina Science Supply Company. The sucrose was obtained at the grocery store as white sugar. The question that we wanted to answer was “Do all sugars undergo yeast fermentation at the same rate?”

Sugar fermentation results in the production of ethanol and carbon dioxide. In the case of sucrose, the fermentation reaction is:

\[C_{12}H_{22}O_{11}(aq)+H_2 O\overset{Yeast\:Enzymes}{\longrightarrow}4C_{2}H_{5}OH(aq) + 4CO_{2}(g)\]

Lactose is also C 12 H 22 O 11  but the atoms are arranged differently. Before the disaccharides sucrose and lactose can undergo fermentation, they have to be broken down into monosaccharides by the hydrolysis reaction shown below:

\[C_{12}H_{22}O_{11} + H_{2}O \longrightarrow 2C_{6}H_{12}O_{6}\]

The hydrolysis of sucrose results in the formation of glucose and fructose, while lactose produces glucose and galactose.

sucrose + water \(\longrightarrow\) glucose + fructose

lactose + water \(\longrightarrow\) glucose + galactose

The enzymes sucrase and lactase are capable of catalyzing the hydrolysis of sucrose and lactose, respectively.

The monosaccharides glucose, fructose and galactose all have the molecular formula C 6 H 12 O 6  and ferment as follows:

\[C_{6}H_{12}O_{6}(aq)\overset{Yeast Enzymes}{\longrightarrow}2C_{2}H_{5}OH(aq) + 2CO_{2}(g)\]

In our experiments 20.0 g of the sugar was dissolved in 100 mL of tap water. Next 7.0 g of Red Star ®  Quick-Rise Yeast was added to the solution and the mixture was microwaved for 15 seconds at full power in order to fully activate the yeast. (The microwave power is 1.65 kW.) This resulted in a temperature of about 110  o F (43  o C) which is in the recommended temperature range for activation. The cap was loosened to allow the carbon dioxide to escape. The mass of the reaction mixture was measured as a function of time. The reaction mixture was kept at ambient temperature, and no attempt at temperature control was used. Each package of Red Star Quick-Rise Yeast has a mass of 7.0 g so this amount was selected for convenience. Other brands of baker’s yeast could have been used.

This method of studying chemical reactions has been reported by Lugemwa and Duffy et al. 2,3  We used a balance good to 0.1 g to do the measurements. Although fermentation is an anaerobic process, it is not necessary to exclude oxygen to do these experiments. Lactose and galactose dissolve slowly. Mild heat using a microwave greatly speeds up the process. When using these sugars, allow the sugar solutions to cool to room temperature before adding the yeast and microwaving for an additional 15 seconds.

Fermentation rate of sucrose, lactose alone, and lactose with lactase

Fig. 1 shows plots of mass loss vs time for sucrose, lactose alone and lactose with a dietary supplement lactase tablet added 1.5 hours before starting the experiment. All samples had 20.0 g of the respective sugar and 7.0 g of Red Star Quick-Rise Yeast. Initially the mass loss was recorded every 30 minutes. We continued taking readings until the mass leveled off which was about 600 minutes. If one wanted to speed up the reaction, a larger amount of yeast could be used. The results show that while sucrose readily undergoes mass loss and thus fermentation, lactose does not. Clearly the enzymes in the yeast are unable to cause the lactose to ferment. However, when lactase is present significant fermentation occurs. Lactase causes lactose to split into glucose and galactose. A comparison of the sucrose fermentation curve with the lactose containing lactase curve shows that initially they both ferment at the same rate.

Fig. 1. Comparison of the mass of CO 2 released vs time for the fermentation of sucrose, lactose alone, and lactose with a lactase tablet. Each 20.0 g sample was dissolved in 100 mL of tap water and then 7.0 g of Red Star Quick-Rise Yeast was added.

However, when the reactions go to completion, the lactose, lactase and yeast mixture gives off only about half as much CO 2  as the sucrose and yeast mixture. This suggests that one of the two sugars that result when lactose undergoes hydrolysis does not undergo yeast fermentation. In order to verify this, we compared the rates of fermentation of glucose and galactose using yeast and found that in the presence of yeast glucose readily undergoes fermentation while no fermentation occurs in galactose.

Fig. 2. Comparison of the mass of CO 2 released vs time for the fermentation of sucrose, glucose and fructose. Each 20 g sugar sample was dissolved in 100 mL of water and then 7.0 g of yeast was added.

Fermentation rate of sucrose, glucose and fructose

Next we decided to compare the rate of fermentation of sucrose with that glucose and fructose, the two compounds that make up sucrose. We hypothesized that the disaccharide would ferment more slowly because it would first have to undergo hydrolysis. In fact, though, Fig. 2 shows that the three sugars give off CO 2  at about the same rate. Our hypothesis was wrong. Although there is some divergence of the three curves at longer times, the sucrose curve is always as high as or higher than the glucose and fructose curves. The observation that the total amount of CO 2  released at the end is not the same for the three sugars may be due to the purity of the fructose and glucose samples not being as high as that of the sucrose.

Fermentation rate and sugar concentration

Next, we decided to investigate how the rate of fermentation depends on the concentration of the sugar. Fig. 3 shows the yeast fermentation curves for 10.0 g and 20.0 g of glucose. It can be seen that the initial rate of CO 2  mass loss is the same for the 10.0 and 20.0 g samples. Of course the total amount of CO 2  given off by the 20.0 g sample is twice as much as that for the 10.0 g sample as is expected. Later, we repeated this experiment using sucrose in place of glucose and obtained the same result.

Fig. 3. Comparison of the mass of CO 2  released vs time for the fermentation of 20.0 g of glucose and 10.0 g of glucose. Each sugar sample was dissolved in 100 mL of water and then 7.0 g of yeast was added.

Fermentation rate and yeast concentration

After seeing that the rate of yeast fermentation does not depend on the concentration of sugar under the conditions of our experiments, we decided to see if it depends on the concentration of the yeast. We took two 20.0 g samples of glucose and added 7.0 g of yeast to one and 3.5 g to the other. The results are shown in Fig. 4. It can clearly be seen that the rate of CO 2  release does depend on the concentration of the yeast. The slope of the sample with 7.0 g of yeast is about twice as large as that with 3.5 g of yeast. We repeated the experiment with sucrose and fructose in place of glucose and obtained similar results.

Fig. 4. Comparison of the mass of CO 2 released vs time for the fermentation of two 20.0 g samples of glucose dissolved in 100 mL of water. One had 7.0 g of yeast and the other had 3.5 g of yeast.

In hindsight, the observation that the rate of fermentation is dependent on the concentration of yeast but independent of the concentration of sugar is not surprising. Enzyme saturation can be explained to students in very simple terms. A molecule such as glucose is rather small compared to a typical enzyme. Enzymes are proteins with large molar masses that are typically greater than 100,000 g/mol. 1  Clearly, there are many more glucose molecules in the reaction mixture than enzyme molecules. The large molecular ratio of sugar to enzyme clearly means that every enzyme site is occupied by a sugar molecule. Thus, doubling or halving the sugar concentration cannot make a significant difference in the initial rate of the reaction. On the other hand, doubling the concentration of the enzyme should double the rate of reaction since you are doubling the number of enzyme sites.

The experiments described here are easy to perform and require only a balance good to 0.1 g and a timer. The results of these experiments can be discussed at various levels of sophistication and are consistent with enzyme kinetics as described by the Michaelis-Menten model. 1  The experiments can be extended to look at the effect of temperature on the rate of reaction. For enzyme reactions such as this, the reaction does not take place if the temperature is too high because the enzymes get denatured. The effect of pH and salt concentration can also be investigated.

• Jeremy M. Berg, John L. Tymoczko and Lubert Stryer,  Biochemistry , 6th edition, W.H. Freeman and Company, 2007, pages 205-237.
• Fugentius Lugemwa, Decomposition of Hydrogen Peroxide,  Chemical Educator , April 2013, pages 85-87.
• Daniel Q. Duffy, Stephanie A. Shaw, William D. Bare, Kenneth A. Goldsby, More Chemistry in a Soda Bottle, A Conservation of Mass Activity,  Journal of Chemical Education , August 1995, pages 734-736.
• Jessica L Epstein, Matthew Vieira, Binod Aryal, Nicolas Vera and Melissa Solis, Developing Biofuel in the Teaching Laboratory: Ethanol from Various Sources,  Journal of Chemical Education , April 2010, pages 708–710.