Kitchen Laboratory II: the CO2 Trap




Introduction: Kitchen Laboratory II: the CO2 Trap

About: Food Chemist, bug lover and enthusiastic crafter with a passion for papercrafts, specially origami

In this instructable, I'll show you how to make the classic natural indicator from red cabbage and then, will use it to demonstrate the production of CO2 during the fermentation process of the yeast Saccharomyces cerevisae.

This is a very simple and fast demonstration, however I think is a nice one and you can show it to your kids, I'm sure they are going to be impressed and they will learn something about bread making.

Step 1: Saccharomyces Cerevisae and CO2

First, let me introduce Saccharomyces cerevisae, this yeast is also known as brewers yeast or beakers yeast and I'm sure you can guess its main uses in Food and Beverage Industry. In this instructable I'm going to explain Sacharomyces role in bread making.

Saccharomyces comes from Greek meaning sugar mould and Cerevisiae comes from the Latin meaning of beer.

Bread making is known since ancient times (archeologists have found evidences of bread making in ancient Egypt.) and Saccharomyces cerevisae is responsible for many of the desirable characteristics in bread.

When Saccharomyces is added to the dough, it changes sugars present in the flour or added to the dough, giving off carbon dioxide (CO2) and alcohol (ethanol). The CO2 is trapped as tiny bubbles in the dough and expands the flour's gluten proteins, and as a result, causes the dough to rise, while alcohol is rapidly evaporated during baking. This process is called fermentation and is the way for gaining energy for many microorganisms

So, in bread making, the carbon dioxide is the more important of the two products, with the evolving gas causing the bread dough to rise. On the other hand, in beer and wine-making, the alcohol is the important product, although the carbon dioxide may be used in beer and champagne.

Shacharomyces is not only important for food and beverage production but for genetic investigation.

Because of the importance of this yeast in Industry and the role of CO2 in breadmaking, I think it could be interesting to use it for the Science Fair contest so I designed this simple experiment to demonstrate the production of CO2 during Saccharomyces cerevisae sugar fermentation.

To do this, we are going to make a very simply home apparatus to collect the CO2 produced during fermentation and then, will conduct it into a red cabbage solution which will act as a pH indicator.

We will need a pH indicator to demonstrate the presence of CO2 because when we make CO2 solution in water it forms carbonic acid (H2CO3), so we can detect the formation of this acid using a pH indicator.

Step 2: Anthocyanins

Red cabbage contains on its leaves, great quantities of anthocyanins with are pigments found in red/purplish fruits and vegetables, Within the plant they serve as key antioxidants and pigments contributing to the coloration of the flowers. But also anthocyanins have the quality to act as a natural pH indicator because it shows color variations depending of the pH of the solution (acidic, basic or neutral)

Other advantage is that we can easily make this pH indicator at home.

Step 3: Materials


A red cabbage
Two small crystal flasks
Aquarium hose (15 cm are enough)
Some modeling clay
Any ammonia based home cleaner (you will only need some drops)
A colander
One package of dry yeast for bakery
A bowl
Some water

Step 4: Making the Indicator

Cut the cabbage into slices and put them into the bowl
Add water enough to cover the slices and soak it for an hour (or boil it for half and hour, but you should let it cool before you can use it)
Using the colander, filter the liquid that now should have a violet color
Congratulations, you have done the indicator

If you have never done this indicator before, maybe you want to experiment with it, feel free to try different substances to find out if they are acidic or basic (some examples are lemon juice, vinegar, baking soda, milk, wine, beer, coke, cleaners, just be cautious and never mix ammonia cleaners with acids because you are going to form NH3 and its fumes are very toxic)

The cabbage indicator color for basic solutions goes from blue to emerald green and from violet to brilliant pink for acids

The cabbage slices are edible and you can use it in a salad.

Step 5: The CO2 Trap

Using the modeling clay, make a cap for one of your flask, insert the aquarium hose in he center and make sure it is completed surrounded by modeling clay to be sure it is sealed (if you don't want to make the whole flask and you have the flask cap, you can make a hole in the center of the bottle cap, introduce the hose and seal it with modeling clay)

Pour some red cabbage indicator on the other flask and add only a few drops, enough to change your indicator into greenish-blue color (do not add too many because is going to be very difficult see the reaction, if your indicator turns green emerald you added more than you needed).

Pour half spoon of sugar in the flask you are going to cover with the cap, add some water; finally add half teaspoon of yeast, mix it very well and cover it with the cap (make sure the cap is sealing very well the flask)

The last but not the least: introduce the free extreme of the hose into the flask that contains the indicator

Now, you just have to sit down and see what happens (it is going to take a half and an hour so please be patient)

After 5 minutes, you will notice that some gas bubbles starts to emerge from the hose very slowly, then the gas flow will become faster.

After and hour or half an hour, you will notice that the liquid is starting to change its color from greenish-blue to light purple.

Success! We just caught CO2 produced from Saccharomyces cerevisae and turned it into carbonic acid. This CO2 is the responsible from producing the classic texture in bread that everyone likes.

Step 6: To Learn More

Hope you enjoyed this demonstration and if you want to learn more or simply make delicious bread, you can try the following books

The Bread Bakers Apprentice Mastering the Art of extraordinary bread

Principles of fermentation technology



    • Organic Cooking Challenge

      Organic Cooking Challenge
    • Fix It! Contest

      Fix It! Contest
    • Game Life Contest

      Game Life Contest

    11 Discussions

    visit our website for educational research works

    It works over a wide range pH
    Check this link, there is a red cabbage pH chart from 1 to 12

    Your picture looks on the alkaline side as compared to the chart, and I know vinegar will give you the pH 1 red - I don't trust that chart. L

    The pKa of Vinegar (acetic acid) is 4.7 (depending on temperature.) I think the actual pH of common household vinegar is somewhere around 2.5.

    But the problem is that vinegar strengths depend on what they are designed for (salad, pickling, etc...)

    Good question though. It's important to find solutions and questions that are posed by a problem

    I looked again, "I made solutions of NaOH or HCl in water" - no buffers...? I have a red cabbage, might test something myself. L

    Both HCL and NaOH do have a certain pKa. They will buffer but the constant of dissociation is high/low (I can't remember which way it goes.) But in practical terms, there is no real effective buffering terms for biological systems.

    Yes you are right, it seems they made the scale without use buffer solutions, but I looked over the net and I found other sites that describes red cabbage indicator. However you will notice that all scales are slightly different. Maybe it depends of the content of anthocyanins in the red cabbage and because is a natural product, I’m sure that the anthocyanin content of the cabbage depends of different factors like season.

    I’m sorry I didn’t pay to much attention to red cabbage indicator because the objective of my instructable was fermentation process and I designed this to be a qualitative demonstration but I think it could be very interesting to make a serious pH scale of red cabbage juice.

    You can see the colors I obtained using different solutions in step 4 (I added notes to the picture so you can now what I used to get these colors.) But some colors like blue are very difficult to get (I got a nice blue color but it lasted only a few seconds)

    If you make your scale please let me know

    Here are the links I found

    Thanks, if I can get some solutions of which I'm sure of pH I'll do something (doesn't seem likeley at the moment though...) L

    simple idea to make a better lid(not as safe though although it'd last alot longer) punch a hole through a mason jar lid and glue the tube into place

    Pretty nifty, I'm sure there's a lot of people that have no idea what's behind fermentation other than it makes you drunk and bubbles. Thanks for the instructable. -Punk