salt and yeast fermentation experiment

April 3, 2014

Single-Celled Science: Yeasty Beasties

A fun fungal activity from Science Buddies 

By Science Buddies

Key concepts Biology Microorganisms Microscopic Metabolism Carbon dioxide   Introduction Did you know that dry yeast is actually alive ? Add the right ingredients, and presto, the mixture becomes a bubbly, oozing mess of life. But just what are the conditions required for this to happen? What does that yeast need to become active and thrive? Try this science activity to find out for yourself!     Background Yeasts are tiny, microscopic organisms—or microorganisms—that are actually a type of fungus. This means that they are more closely related to a mushroom than to plants and animals or bacteria (the latter of which are also microorganisms). These little critters might sound strange and different, but people have been using them for thousands of years to make bread rise. How does this work? It has to do with the metabolism of the yeasts, or, in other words, what they eat and what they turn that food into.   Like us, yeasts must get their food from their surrounding environment to grow and reproduce—that is, to make more yeast. What do they eat? Yeasts feed on sugars and starches, which are abundant in bread dough! They turn this food into energy and release carbon dioxide gas as a result. This process is known as fermentation. The carbon dioxide gas made during fermentation is what makes a slice of bread so soft and spongy. The pockets of gas are produced by yeasts when the dough is allowed to rise before baking. Materials

Three plastic two-liter bottles

Measuring tablespoon

White table sugar

Salt, baking soda or vinegar

Permanent marker (optional)

Measuring cups

Warm tap water

One medium-sized pot or bowl, at least two quarts in size

Six packets of dry yeast or an equivalent amount from a jar

Three standard-sized latex balloons

Clock or timer

  Preparation

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Rinse each bottle thoroughly with water and remove any labels.

Add two tablespoons of sugar to two of the three bottles. How do you think the sugar will affect the activity of the yeast?

To one of the bottles that you added sugar to, also add two tablespoons of salt, baking soda or vinegar. How do you think adding salt, baking soda or vinegar will affect the activity of the yeast?

Throughout the experiment, keep track of what you added to each bottle. If needed, you can label the bottles with a permanent marker.

  Procedure

Fill the medium-sized pot or bowl with at least eight cups of very warm tap water. Adjust the temperature of the hot water coming from the tap until it is almost too hot to hold your hands under. Use this temperature of water to fill the pot.

Using the warm water from the pot, fill each bottle with about two and one-half cups (or about one-third full). Put the lid back on to each bottle and shake them each thoroughly to dissolve all of the ingredients.

To each bottle, add two packets of dry yeast (or an equivalent amount from a jar). Put the lid back on to each bottle and shake each one gently to mix in the yeast.

Remove each lid and stretch a balloon completely over the opening of the bottle (over all of the ridges). Why do you think it is important to form a tight seal with the balloon on the bottle’s opening?

Leave the bottles to rest in a warm location for 45 minutes. Keep the balloons out of direct sunlight. How do the balloons change over time?

After 45 minutes, examine the bottles and the balloons. Which balloons have become inflated? How big are they compared to each other? Do you notice any differences in the contents of the bottles?

In which environment did the yeast make the most carbon dioxide? What does this tell you about the conditions needed for yeast fermentation to take place? 

Extra: You could quantify your results from this activity by using a water displacement test. To do this, you could fill a large pot completely full with water, place it in a larger tray, pan, or pot. Quickly tie off the balloon you would like to measure without letting gas escape, and then submerge the balloon in the water. You can measure how much water overflowed from the pot into the tray to determine how much water the balloon displaced, and consequently the volume of the carbon dioxide gas inside the balloon. If you quantify your results, exactly how different are the sizes of the balloons?

Extra: Another environmental condition that can affect the activity of yeast and the process of fermentation is temperature. You could explore this by preparing several bottles using the same conditions, and then placing each bottle in a different place with a different temperature. After 45 minutes, how do the balloons vary in size?

Extra: You could try this activity again, but next time just focus on how using different types and sources of sugars affect the carbon dioxide production. How do the sugars from different juices or other sources affect how much carbon dioxide is produced ?

  Observations and results Did the balloon on the bottle with only yeast and water remain un-inflated? Did the balloon on the bottle with only sugar added inflate the most?   When yeasts eat sugar and turn it into energy, they also produce carbon dioxide. This process is known as fermentation. In this activity, the balloons on the bottles should have captured carbon dioxide produced by the yeasts during fermentation. In the bottle that contained yeasts but not sugar, the yeasts did not have food (i.e., sugar) so the balloon should not have inflated. In the bottle that contained yeasts and sugar (but not salt, baking soda or vinegar), the yeasts should have thrived and made a lot of carbon dioxide, clearly inflating the balloon. When salt, baking soda or vinegar was added, the yeasts should have made less carbon dioxide, inflating the balloon less than when only sugar was used. This is because the addition of these substances changed the environment and made it less ideal for the yeasts. Specifically, adding salt increased the salinity of the environment, and adding baking soda or vinegar changed the pH of the environment, making it more basic or acidic, respectively, compared to the neutral environment provided by the plain water.   Cleanup When you are done with this activity, dispose of the yeasts by composting them or (with permission) dumping them outside somewhere. Do not pour the yeasts down the drain without diluting them with water, as they may damage pipes when they expand.   More to explore Fun Facts About Fungi: Fermentation , from Utah State University Experiments with Acids and Bases , from Fun Science Gallery Fun, Science Activities for You and Your Family , from Science Buddies Yeasty Beasties , from Science Buddies  

This activity brought to you in partnership with Science Buddies

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.

More about April 2015

Department of Chemistry 200 University Ave. W Waterloo, Ontario, Canada N2L 3G1

[email protected]

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3.1.3 Yeast experiment explained

You’ve seen the results of the yeast experiment, but what do these results mean?

Yeasts are microscopic, single-celled organisms, and are a type of fungus that is found all around us, in water, soil, on plants, on animals and in the air. Like all organisms, when yeasts are put in the right type of environment they will thrive; growing and reproducing.

Your experiments were designed to help you identify which environment promotes the most yeast growth. The first three glasses in your experiment contained different temperature environments (cold water, hot water and body temperature water). At very low temperatures the yeast simply does not grow but it is still alive – if the environment were to warm up a bit, it would gradually begin to grow. At very high temperatures the cells within the yeast become damaged beyond repair and even if the temperature of that environment cooled, the yeast would still be unable to grow. At optimum temperatures the yeast thrives.

Your third and fourth glasses both contained environments at optimum temperature (body temperature) for yeast growth, the difference being, the fourth glass was sealed. The variable between these two experiments was the amount of available oxygen. You may have been surprised by your results here, thinking that a living organism in an environment without oxygen cannot survive? However, you should have found that yeast grew pretty well in both experiments.

To understand why yeast was able to thrive in both conditions we need to understand the chemical process occurring in each glass during the experiment. In the three open glasses, oxygen is readily available, and from the moment you added the yeast to the sugar solution it began to chemically convert the sugar in the water and the oxygen in the air into energy, water, and carbon dioxide in a process called aerobic respiration.

Yeast is a slightly unusual organism – it is a ‘facultative anaerobe’. This means that in oxygen-free environments they can still survive. The yeast simply switches from aerobic respiration (requiring oxygen) to anaerobic respiration (not requiring oxygen) and converts its food without oxygen in a process known as fermentation. Due to the absence of oxygen, the waste products of this chemical reaction are different and this fermentation process results in carbon dioxide and ethanol.

Depending on how long you monitored your experiment for and how much space your yeast had to grow you may have noticed that, with time, the experiment sealed with cling film slowed down. This is for two reasons; firstly because less energy is produced by anaerobic respiration than by aerobic respiration and, secondly, because the ethanol produced is actually toxic to the yeast. As the ethanol concentration in the environment increases, the yeast cells begin to get damaged, slowing their growth.

The ethanol produced is a type of alcohol, so it is this process that allows us to use it to make beer and wine. When used in bread making, the yeast begins by respiring aerobically, the carbon dioxide from which makes the bread rise. Eventually the available oxygen is used up, and the yeast switches to anaerobic respiration producing alcohol and carbon dioxide instead. Do not worry though; this alcohol evaporates during the baking process, so you won’t get drunk at lunchtime from eating your sandwiches.

Incorporate STEM journalism in your classroom

• Exercise type: Activity
• Topic: Microbes

Fermentation and Pasteurization in the classroom

• Download Student Worksheet

Purpose: Students will learn about pasteurization by performing an experiment that involves calculating and interpreting results.

Procedural overview: Students will annotate and analyze “ Louis Pasteur’s devotion to truth transformed what we know about health and disease ” from Science News online. After learning about Pasteur’s discoveries and how he developed the pasteurization process, students will do a hands-on experiment. In this experiment, yeast solutions will be prepared at different temperatures and then monitored for gas production. Students will collect data on gas production by measuring how big the gas makes a balloon and will approximate the volume of gas produced. The data will be graphed and interpreted by students to identify the temperature that pasteurization occurs. As an optional activity, students will further study the importance of pasteurization in food production and in the prevention of foodborne illness.

Approximate class time: 2 class periods

Bunsen burner

Thermometer

Whiteboard/chalkboard

Yeast (Make all packets the same brand)

Scale (Alternative: tablespoon or disposable plastic spoon)

Stopwatches

Plastic bottles of the same size, (1 liter or 1.25-liter bottles recommended)

Round balloons

Tape measures (Alternative: rulers and string/yarn)

Student worksheet

Directions for teachers:

Before the start of class, set up the experiment. Around the lab, set up stations with a Bunsen burner, a beaker to heat water, a funnel, a bottle, a thermometer, a yeast packet, a stopwatch, a tape measure and a balloon. Have one or two weighing stations where students can weigh sugar and yeast.

In class, have students read the introduction and the section call “How Pasteur developed pasteurization” in “ Louis Pasteur’s devotion to truth transformed what we know about health and disease .” This article appeared in the November 19, 2022, print edition of Science News with the title “Louis Pasteur’s Long Legacy.” Ask students to annotate the article as they read and identify any new vocabulary and concepts.

Article analysis

After students have read and done their annotations, have them answer the following questions.

1. Who was Louis Pasteur?

Louis Pasteur was a French chemist and biologist, who was born in 1822.

2. How was tartaric acid important to Pasteur’s career?

Pasteur’s work on tartaric acid and wine got him started on work that eventually led to discoveries about microbes and diseases.

3. Why was it important that Pasteur showed yeast are living things?

Until Pasteur’s work, most scientists thought that fermentation was a “natural nonbiological chemical process.” Demonstrating that yeast are living organisms changed how scientists thought about fermentation.

4. Microorganisms are living things too small to see with the naked eye and include fungi and bacteria. What kind of microbe is a yeast?

Pasteur thought yeast was a “small plant,” but it really is a kind of microscopic fungus.

5. What do yeast do with sugar, and what is the process called?

Yeast can convert sugar to alcohol in a process called fermentation.

6. Why do yeast ferment?

Fermentation is how yeast meet their nutritional (energy) needs.

7. People use fermentation to make wine, beer and other products. But sometimes those products can become spoiled or get contaminated with microbes that are harmful. What method of food and beverage protection did Pasteur develop, and how does it work?

Pasteur created pasteurization, a method of heating that kills microorganisms that can spoil food items or cause disease.

8. What questions do you have about the fermentation process? What might you want to investigate about pasteurization?

Student answers will vary. When you make yogurt, how much can you change the flavor by changing the bacteria you add to the milk? I would like to do an experiment with raw milk. My question: If you start with raw milk, and it starts to sour because of the microbes that are present, can you reverse or minimize the souring by pasteurizing the sour milk?

Preparing to do the experiment

Review fermentation and introduce the chemistry behind it. Include any of the following information that you find useful.

Pasteur thought yeast was a “small plant,” but today we know that it is really a microscopic fungus. However, Pasteur was right in thinking that yeast metabolizes sugar in a process called fermentation. In this process, yeast consumes sugar to produce carbon dioxide, ethanol and energy (in the form of ATP).

C 6 H 12 O 6 –> 2C 2 H 5 OH + 2CO 2 + 2ATP

Sugar –> ethanol (alcohol) + carbon dioxide + energy

Humans have used yeast to ferment food items for thousands of years. Because yeast creates ethanol, a type of alcohol, it is used to make alcoholic beverages like beer and wine. Yeast is also important in breadmaking. When the yeast in bread dough ferments, carbon dioxide is produced. The carbon dioxide helps the bread rise.

In this experiment, students will determine the temperature at which pasteurization occurs for a yeast solution. Pasteurization occurs when the yeast have died. Ideally, you should not give the students hints about the temperature at which pasteurization occurs.

Before starting the experiment, discuss the concept of a control in a science experiment and what might be possible options for a control in this study. Remind students of the importance of multiple trials; ask that each group test at the control temperature and one of the other nine temperatures. Also, they should do at least two trials at each of their temperatures, if there are enough materials and time. Two separate student groups could also test at the same temperature.

Cover lab safety. At the highest temperatures, the students could burn themselves if they do not pour carefully.

After mixing yeast, water and sugar together in a bottle, the students will top the bottle’s opening with a balloon to capture any gas produced. The water used in the bottles will be varied in temperature so students can find out for themselves at what temperature yeast cells die and pasteurization occurs.

Students will need it to calculate the volume of gas produced during fermentation. Review this volume formula, where c is circumference, V=(c 3 )/(6π 2 )  and note that the unit students will use is cubic centimeters cm 3 .

The amount of information you give students can vary depending on the time available. However, students will feel more ownership over their experiment and their findings if they help decide how to set up the experiment.

Use the following questions to guide students in setting up the lab and determining experimental variables.

1. Yeast produces carbon dioxide, a gas, as it ferments sugar. What do you expect will happen to the balloons?

The balloons will inflate with carbon dioxide as the yeast cells break down the sugar into carbon dioxide, alcohol and energy.

2. How do you think the water temperature will affect gas production?

Initially, as the temperature increases, the amount of gas produced will also increase. Once the temperature is hot enough for pasteurization to occur, gas production will begin to decrease or will stop entirely as the yeast cells die.

3. The data you collect in this experiment will be graphed. What units will you use on the x axis and the y axis?

The x axis will show temperature in degrees C. Depending on how students are measuring the gas produced, the y axis will show the amount of carbon dioxide, indicated by either the circumference or volume of the balloon.

4. What temperatures should the class test (starting at room temperature, approximately 22° C)? (Note that each group should run trials at the control temperature and one other temperature.)

Student answers will vary. We should test at 22° C, 28° C, 34° C, 40° C, 46° C, 52° C, 58 ° C, 64° C,  70° C and 76° C.

5. What should the control group be in this experiment?

A bottle with water, sugar and no yeast at room temperature; a bottle with water, no sugar and no yeast at room temperature; or a bottle with water, yeast and no sugar at room temperature.

6. What should be the length of time for each trial? Twenty minutes.

7. If time permits, how many trials should ideally be run at each temperature?

Two or three trials.

8. How can we measure the amount of gas produced, and what scientific unit could we use?

Student answers will vary. We could figure out the amount of gas produced after measuring the balloon’s volume. To get to volume, we will need to know the circumference of the balloon to put into the volume formula. The unit to use is cubic centimeters (cm 3 ).

Fermentation experiment

Ask the class to decide what temperatures they want to test. Try to have the students evenly space the temperatures. For example, temperatures could increase in 6-degree increments: 22° C, 28° C, 34° C, 40° C, 46° C, 52° C, 58° C, 64° C, 70° C and 76° C. Temperatures should not go above 80° C.

The students also must agree on how much sugar, yeast and water they want to use in their bottles and in what order they want to combine their materials, or you could suggest 250 ml of water, 40 grams (3 tablespoons) of sugar and the contents of one yeast packet. All yeast packets should be the same brand and at room temperature. Whatever the students decide, please emphasize that each group should use the same amount of sugar, yeast and water. Only the control will have different amounts of sugar and/or yeast.

Have the students form groups. Each group would ideally do multiple trials on the control temperature and one other temperature. In setting up, each group should put the sugar and yeast in the bottle, and then heat their water beaker over the Bunsen burner. As the water heats, carefully check the temperature. When the water reaches the group’s study temperature, students should carefully pour 250 ml of water through a funnel into their bottle, screw on the bottle’s lid and shake the bottle to mix the water, yeast and sugar. The temperature of the water might cool during its transfer into the bottle. This could result in some experimental groups showing carbon dioxide production when the yeast should have been killed by pasteurization.

Once the bottle’s contents are combined, students should unscrew the bottle, place a balloon on the top of the bottle and start a 20-minute timer. As each group’s timer ends, the group should measure the circumference of their balloon at the widest point using a tape measure and record the circumference on their worksheet and on the board. Then use the formula V=(c 3 )/(6π 2 ) , to calculate the volume of carbon dioxide produced and graph the volume of gas produced using metric units for the volume and degrees Celsius for the temperature.

Ask the students to answer the following questions about their experimental results.

1. Measure the circumference of your group’s balloon and record it in your chart and on the board. Calculate the volume of your group’s balloon and add the data to the chart using the formula: V=(c 3 )/(6π 2 ) , where c represents the circumference. Continue to fill in the chart as other groups add their data to the board. (Students will use the chart in the student worksheet.)

Student answers will vary, but should follow this trend: Circumference and volume should go up for 28 ° C and 34° C. For high temperatures, circumference and volume should trend downward.

2. Graph the volumes from each group. Remember to label your graph and axes. (The graph is available in the student worksheet.)

Graphs will vary. The x axis should be for temperature in degrees Celsius; the y axis is for volume of carbon dioxide in cubic centimeters. Temperature should be marked every six spaces; the line on the graph climbs until about 34 degrees or a little higher, and then moves steadily downward until the volume of carbon dioxide tapers to zero. A possible label for the chart could be “Volume of Carbon Dioxide Produced from Yeast Fermentation.”

3. Why is it important to record what happens with the control group?

If the control group shows that gas has been produced, then there might be other microorganisms that could skew the data.

4. What is the relationship between gas volume and temperature?

Initially, the volume of carbon dioxide produced increases as temperature increases. However, eventually the volume of carbon dioxide produced begins to decrease.

5. At what temperature did the most fermentation occur? How could you tell?

Student answers will vary. For example, the temperature at which most fermentation occurred was 34 ° C because the largest volume of carbon dioxide was produced at 34 ° C.

6. At what temperature did yeast stop fermentation and gas production? How could you tell?

Student answers will vary. I think fermentation started slowing down when temperatures got into the 60s. As temperatures went higher and higher, there was less carbon dioxide produced. The highest temperatures killed the yeast, preventing them from fermenting the sugar and producing carbon dioxide. There was less carbon dioxide in the balloons at higher temperatures.

7. How might we know that the yeast died due to pasteurization?

Student answers will vary. We know that carbon dioxide is produced during fermentation. As temperatures rise, there will come a point when fermentation slows as yeast cells die. If the balloon does not inflate much, it suggests that carbon dioxide production is declining and that yeast are likely dying. Assuming nothing went wrong with the experiment, pasteurization probably occurred if the balloon does not inflate at all.

8. How has learning about Pasteur’s discoveries influenced your views about what you eat?

Student answers will vary. I am more aware of how important pasteurization is for protecting our food supply.

9. What other question would you like to answer about microorganisms in food?

Student answers will vary. Do different microorganisms get killed through pasteurization at different temperatures?

Activity extension: After students perform the experiment, you can ask them to learn about foodborne illnesses that can be prevented by pasteurization and to create a poster explaining how pasteurization protects people from these illnesses.

The following questions can serve as prompts. If students want to, they can ask their own questions.

1. What is a foodborne illness?

A foodborne illness is a disease that is spread by the consumption of contaminated food.

2. Name a foodborne illness that can be caused by drinking contaminated milk.

Student answers will vary. Listeriosis and tuberculosis are two diseases that can be spread in unpasteurized milk.

3. What are the symptoms of this disease?

Student answers will vary. Listeriosis can cause fever, muscle aches, loss of balance and seizures.

4. Have there been any recent outbreaks of this disease? If so, what food products caused this outbreak?

Student answers will vary. In 2022, people developed listeriosis after eating deli meats and cheeses and ice cream contaminated with Listeria .

5. Even pasteurized food can cause foodborne illnesses. Why is this the case?

Microorganisms could be introduced after the food was pasteurized or the disease was caused by a microorganism that was not killed by pasteurization.

6. Create a poster that shows how pasteurization protects people from your foodborne illness.

Student products will vary but should all mention pasteurization.

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How Would Salt Affect Yeast?

How Enterococcus Faecalis Changes the Mannitol Salt Plate

Salt can have a negative effect, a positive effect or no effect on yeast. Salt draws water from everything around it and the effect of salt on yeast depends of the ability of a particular species to cope with salt trying to draw essential water away from the yeast cell, also known as osmotic stress.

While Making Bread Dough

Although salt can give dough added seasoning, too much salt can have a negative effect on baker's yeast. The cell wall of bread-making yeast is semi-permeable; when a significant amount of salt is nearby, a yeast cell will release water. Because this water is necessary for its cellular activities, releasing it will slow down the reproduction and fermentation activities of the yeast. Knowing this, bread and pizza makers will base the amount of salt in their dough partially on how active they want their yeast to be.

On the Fermentation Process

According to a 2010 report in the International Journal of Wine Research, salt boosts the activity of the wine-making yeast Saccharomyces cerevisiae. The European study team found that exposing yeast to a high-salt solution increased the fermentation activity of the yeast. They speculated that exposure to the high-salt solution caused the yeast to produce protective metabolites. These metabolites could have guarded the yeast against osmotic stress and the toxicity of ethanol produced during the fermentation process.

Effect on a Yeast Infection

Although it has not been shown to be an effective cure, a salt bath is often recommended as a home remedy to treat symptoms of a common yeast infection caused by Candida albicans. However, a similar strain of yeast, Candida dubliniensis, is much more susceptible to the osmotic forces created by salt. According to a 2010 report by researchers at Trinity College in Dublin, Ireland -- a C. albicans gene called ENA21, which is known play a role in pumping sodium out of C. albicans, seems to make it more pathogenic than C. dubliniensis.

Yeast Adapting to Salt Concentrations

In 2011, researchers at McGill University revealed that baker's yeast is capable of adapting to high concentrations of salt via evolution. The researchers found that the degree and pace of change of the yeast's environment and the amount of previous exposure to a high-salt environment all played a role in determining whether the yeast would evolve. The team noted that "rescue by evolution" happened relatively fast during their trials, taking place within 50 to 100 generations.

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• King Arthur Flour: Salt
• International Journal of Wine Research: Influence of Sodium Chloride on Wine Yeast Fermentation Performance
• International Journal of Microbiology: Candida albicans Versus Candida dubliniensis: Why Is C. albicans More Pathogenic?
• McGill University: Evolution to the Rescue

About the Author

Brett Smith is a science journalist based in Buffalo, N.Y. A graduate of the State University of New York - Buffalo, he has more than seven years of experience working in a professional laboratory setting.

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cmfotoworks/iStock/Getty Images

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What does salt do to yeast?

In this article:

Salt has a significant impact on yeast and its ability to leaven bread dough. When yeast is mixed with salt, it can slow down the fermentation process, as salt draws water from the yeast cells through osmosis. This can result in a longer rise time for the dough, as the yeast becomes less active. Additionally, high levels of salt can inhibit the activity of yeast altogether, preventing it from producing the carbon dioxide gas that gives bread its airy texture. Therefore, it’s crucial to use the right amount of salt when working with yeast to ensure that the bread rises properly and has the desired texture and flavor.

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How does salt affect the fermentation process?

The presence of salt in dough can have a significant impact on the fermentation process. Salt can regulate the rate of fermentation, slowing it down and allowing for more complex flavor development in the dough. However, excessive amounts of salt can hinder the fermentation process, leading to a less active yeast and a denser bread texture. It’s important to strike a delicate balance when incorporating salt into bread dough to achieve the desired fermentation and bread texture.

Does salt kill yeast?

While salt can slow down the activity of yeast, it does not necessarily kill it. However, using too much salt can inhibit yeast activity to the point where it cannot effectively leaven bread dough. Therefore, it’s important to use salt in moderation when working with yeast to ensure that the fermentation process is not overly hindered.

How much salt is ideal when using yeast?

The ideal amount of salt to use when working with yeast varies depending on the recipe and personal preference. In general, around 1-2% of the flour weight is a common recommendation for salt in bread recipes. However, specific salt levels may need to be adjusted based on the type of bread being made and individual taste preferences. It’s important to experiment with salt levels when baking with yeast to find the perfect balance for your desired bread texture and flavor.

Can I omit salt when using yeast?

While it is possible to bake bread without salt, it is not recommended. Salt plays a crucial role in regulating yeast activity and flavor development in bread dough. Without salt, the fermentation process may occur too quickly, resulting in a less-developed bread flavor and texture. Additionally, salt contributes to the overall balance of flavors in bread, so omitting it can lead to a bland and unappealing end product.

What are the effects of using too much salt with yeast?

Using too much salt when working with yeast can have several negative effects on bread dough. Excessive salt can inhibit yeast activity, leading to a longer rise time and a denser bread texture. It can also hinder the fermentation process, resulting in a less developed and complex flavor in the bread. Additionally, highly salted dough can be unappealing in taste and may be unsuitable for certain dietary restrictions. Therefore, it’s important to use salt in moderation when baking with yeast to achieve the best results.

How can I adjust salt levels in a yeast recipe?

When working with yeast, it’s essential to pay attention to the salt levels in your dough and make adjustments as needed. If a recipe calls for a specific amount of salt, consider gradually reducing or increasing the salt to suit your taste preferences. It’s important to keep in mind that salt levels can affect the fermentation process and the overall flavor of the bread. Therefore, it’s crucial to balance salt levels with the desired texture and taste of the final product.

What types of bread are sensitive to salt levels in yeast?

Different types of bread can be sensitive to salt levels when working with yeast. For example, sourdough bread, which relies heavily on the fermentation process, can be affected by excessive salt, resulting in a less active yeast and a flatter bread texture. Similarly, delicate and lightly flavored bread, such as brioche, may be sensitive to salt levels, as excessive salt can overpower the subtle flavors in the dough. It’s important to consider the type of bread being made when adjusting salt levels to achieve the best results.

How does salt impact the texture of bread made with yeast?

Salt plays a crucial role in the texture of bread made with yeast. When used in the right amounts, salt can help regulate the fermentation process, leading to a lighter and more airy bread texture. However, excessive salt can hinder yeast activity, resulting in a denser and less developed bread texture. It’s important to use salt in moderation when working with yeast to achieve the desired bread texture and overall quality of the final product.

What are the key considerations when adding salt to yeast dough?

When adding salt to yeast dough, it’s important to consider several key factors. First, be mindful of the type of bread being made and how sensitive it may be to salt levels. Additionally, consider the overall flavor profile of the bread and how salt can contribute to its balance of flavors. It’s also essential to factor in personal taste preferences and adjust salt levels accordingly. Experimenting with different salt levels in bread recipes will help you find the perfect balance and achieve the desired texture and flavor in your bread.

Can salt affect the rising time of bread dough made with yeast?

Yes, salt can significantly impact the rising time of bread dough made with yeast. When salt is present in the dough, it can slow down the fermentation process, resulting in a longer rise time. This can be beneficial in developing more complex flavors in the bread. However, excessive salt can inhibit yeast activity to the point where the dough rises too slowly or not at all. It’s important to strike a balance when incorporating salt into bread dough to achieve the right rise time for the desired bread texture and flavor.

How does salt interact with yeast in bread baking?

The interaction between salt and yeast in bread baking is crucial to achieving the desired texture and flavor. Salt can regulate the activity of yeast, slowing down the fermentation process and allowing for more flavor development in the bread. However, excessive salt can hinder yeast activity, resulting in a less active fermentation process and a less developed bread texture. It’s important to carefully consider the salt levels in bread recipes to achieve the best results when baking with yeast.

Most people are familiar with the sweet and savory taste of fresh baked goods. This might be French bread, sourdough, bagels, or even pizza dough. No matter the type of bread, baking goods all require yeast, along with a few other ingredients to help the process. Typically, there is flour, sugar, warm water and so on. However, very few people realize that salt is an essential ingredient that plays a significant role in bread making, especially when yeast is involved. Salt inhibits fermentation by dehydrating yeast and gluten, yet it is crucial to the breads flavor. In addition, salt acts as a preservative by retarding spoilage.

It’s important to keep in mind that different types of bread require different salt contents. Getting the correct salt measurements for bread doesn’t have to be an issue. Even though it may seem like a simple ingredient within the dough, its salt that enhances the bread to taste better than it naturally would. But, used haphazardly within a recipe can break the dough down, making it inedible. So, What are the ideal salt measurements for yeast, you ask? A healthy amount simply depends on your specific recipe with a general rule of thumb being between 1-2% weight of flour. This small amount, when combined, can transform your bread into a delightful mix of perfection.

Watch this awesome video to spice up your cooking!

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About Julie Howell

Julie has over 20 years experience as a writer and over 30 as a passionate home cook; this doesn't include her years at home with her mother, where she thinks she spent more time in the kitchen than out of it. She loves scouring the internet for delicious, simple, heartwarming recipes that make her look like a MasterChef winner. Her other culinary mission in life is to convince her family and friends that vegetarian dishes are much more than a basic salad. She lives with her husband, Dave, and their two sons in Alabama.

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Experimenting With Yeast

All of our food comes from the living world around us. Most of it it is made from plants and animals, but other living things go into our food, too. Today, we’re going to explore one of these other ingredients, called fungus (if there’s only one, we call it fungus; if there are many, they are fungi). Fungi are found nearly everywhere and play important roles in our world. They can help break down dead plants and animals, returning them to the earth. Some fungi can cause diseases. And there are some fungi that we eat, like mushrooms. 

About the Experiment

For this experiment, we’re going to learn about a very small fungus, called yeast. You can’t see a single yeast with your eyes, but if you put a lot of yeast together, you can get a gooey lump (if they’re wet) or a powder (if they’re dry). Yeast are one of the most important ingredients in bread. Let’s find out how this special fungus helps us make bread.

  What You'll Need

• Measuring cups and spoons, bowls, mixing spoons, 2 baking pans, oven
• Active dry yeast
• Warm (not hot!) water
• Butter or similar product to grease pans

Let's Do This!

The yeast you buy in stores is alive. It may not seem like it because it’s just a dry powder, but the yeast are just resting, until we tell them it’s time to wake up and get going. How do we do that? Just add a little water – and sugar.

• Begin by preheating your oven to 450 degrees.
• Activate the yeast by mixing it with ¼ cup of warm water and a teaspoon of sugar, then wait for about 15 minutes. In a second bowl, add just the yeast and water, but no sugar. Does the yeast react the same way with or without the sugar? Why do you think this is happening? (After observing the two mixtures, discard the one without the sugar)
• Mix 2 tsp of yeast with 3 cups of flour and 2 tsp of salt. Add another cup of warm water. Stir until it’s all combined into a doughy blob. If needed, add a little more warm water until the mixture sticks together. In a separate bowl, mix the same ingredients – but without the yeast.
• Cover both bowls and leave them out at room temperature for 2-3 hours. The room should be warm, at least 70 degrees. What happens to the mixture in each bowl at the end of the time?
• Sprinkle some flour on a table or surface to shape the dough, then place the dough on top of it. Fold the dough into a round shape, then push down on it to squeeze out the air bubbles. Do this once or twice more. Repeat with the other dough.
• Grease the inside of the pans with butter or a similar product and place the loaves into the pans. Note which pans have the dough with and without the yeast.
• Bake for 30-40 minutes, checking periodically to see how the loaves look. Watch their color and take them out when they begin to turn golden brown. Let them cool for about 10 minutes before cutting into them. What does each loaf look like when you cut into it? How does it taste?

What Did You Learn?

• What happened to the loaves with and without the yeast? Why?
• Did the two loaves taste different? What about their texture (how they felt)? Would you want to eat bread made without yeast?
• Is what happened to the bread the same as what happens when soda or other drinks have bubbles in them? How is it the same or different?
• What the yeast did with the sugar and the water is a process called fermentation . The yeast changed the sugar into a kind of gas, called carbon dioxide. Do you think any of the other foods that you eat are made using fermentation?

To see how else scientists are experimenting with yeast, check out the resources below.

It’s not just for food – some scientists are using yeast to make fuel for cars too.

Yeast might even help feed astronauts in space.

Where does the yeast we use in baking come from?

Scientists are exploring whether foods made with fermentation are especially good for us, by helping to feed the bacteria in our stomachs. Bacteria are living things that are too small to see, but all around us.

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Question: Question 5: Describe an experiment you could perform to test the effect of salt on yeast fermentation. You have all of the supplies available to you that were used in the virtual lab as well as solutions containing 2% NaCl, 10% NaCl, and 20% NaCl. Your experiment must include a negative control and a positive control and must use test all 3 salt solutions.

In order to examine the effect of salt in fermentation, the presence of sodium chloride during fermentation was examined.yeast was allowed to ferment in different anaerobic environment with varying levels of salt concentration inorder to determine th …

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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.

More Fun Science Experiments

Explore chemistry , biology and more, including…

• Bread Mold Experiment
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• Bread In A Bag
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Helpful Science Resources To Get You Started

Here are a few resources that will help you introduce science more effectively to your kiddos or students and feel confident presenting materials. You’ll find helpful free printables throughout.

• Best Science Practices (as it relates to the scientific method)
• Science Vocabulary
• All About Scientists
• Free Science Worksheets
• DIY Science Kits
• Science Tools for Kids
• Scientific Method for Kids
• Citizen Science Guide
• Join us in the Club

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• 90+ classic science activities  with journal pages, supply lists, set up and process, and science information.  NEW! Activity-specific observation pages!
• Best science practices posters  and our original science method process folders for extra alternatives!
• Be a Collector activities pack  introduces kids to the world of making collections through the eyes of a scientist. What will they collect first?
• Know the Words Science vocabulary pack  includes flashcards, crosswords, and word searches that illuminate keywords in the experiments!
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