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Investigating Alcoholic Fermentation and the Affects of Yeast on Dough

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Biology Lab Report

Investigating Alcoholic Fermentation and the Affects of Yeast on Dough

Aim: The aim was simply to investigate whether or not yeast had any affect on causing dough to rise when baked and to experiment with alcoholic fermentation eg. to see if it gave off carbon dioxide.


Introduction: Following a few weeks of fermentation theory, groups of three to four were assigned and told to conduct a series of experiments involving the affects of fermentation. My group consisted of myself, Won Jin, Brendan and Sun-Ho and we chose to investigate alcoholic fermentation and the affects of yeast on dough, more specifically to see if yeast caused the dough to rise in anyway. We followed the instructions in our biology textbook on page 129.


Hypothesis: According to what I’ve learned, I would expect that the yeast does indeed cause the dough to rise due to the carbon dioxide gas given off by the yeast. For our alcoholic investigation, I can safely assume that carbon dioxide will be given off as the formula for anaerobically respiration in alcoholic fermentation for turning glucose into alcohol is [ Glucose -> Alcohol + Carbon Dioxide + Energy ] so obviously Carbon Dioxide is a part of this. Also I assume that the fermentation will give off heat and the sugar will probably be turned into alcohol.

Materials:     ca. 100 g flour
          Water
          Yeast
          10 per cent solution Glucose
          Liquid Paraffin
          Four Test Tubes
          Lime Water (Used as an indicator)


Practical: Our first experiment was to see if yeast impacted dough in anyway and to do this we brought in supplies such as flour and yeast. We followed the instructions and made three groups of dough. For each group we added 50 g of flour and added a little bit of water while mixing it. Due to my lack of “kitchen skills” I had to throw away my first two attempts, as they had gotten too sticky. But like they say, third time’s the charm and we finally made suitable dough.

We mixed warm water and yeast together in a bowl and added about 10 g of sugar, which is necessary for the dough to expand. We split the dough into two smaller mounds and added the yeast solution with only one of them to see the difference of dough with yeast and dough without yeast subjected to the same conditions to analyse the difference.

We placed both mounds of dough on top of a windowsill where we would leave it for an hour. We though this was a suitable place as the sun had already caused the surface to warm up. After an hour, the Dough mound with yeast did rise while the Dough mound without, didn’t. Not much of a surprise. I’ll return to the rest of our results in my conclusion.


For our second experiment (Alcoholic Fermentation) we moved to the Chemistry lab, from the kitchen, in order to better our chances of conducting a good experiment in a suitable environment. Our teacher, Mr. Barling, provided the Liquid Paraffin used in this experiment.

We poured the 10 per cent Glucose solution into a test tube and boiled it to be rid of any excess oxygen that could contaminate the experiment by affecting the yeast. After cooling the test tube, we added a little Yeast and poured a thin layer of Liquid Paraffin to, once again, stop oxygen from reaching the yeast. The layer of Liquid Paraffin created a surface on top of the Glucose/Yeast solution disabling any foreign gasses to mix with it. To better conduct the experiment, we set up an additional test tube and followed the instructions exactly, except this time we didn’t add any Yeast to the Glucose in order to see if Yeast really did cause the Glucose to ferment into Alcohol.

To determine if Yeast in Alcoholic Fermentation gives off Carbon Dioxide, we made another test tube with Lime Water in it and connected a tube leading from the first Test Tube to the container with Lime Water in it. Through the Test Tube, we hoped that the Carbon Dioxide given off would travel through the tube and turn the Lime Water (used as an indicator) into a milky colour. Without much surprise it did and we could conclude that the Yeast did give off Carbon Dioxide, much like our previous experiment (Carbon Dioxide given off by the Yeast causing the Dough to rise).


Conclusion: From our results I can safely assume that my Hypothesis was correct for both experiments and I can now, for sure, say that Yeast does cause Dough to rise. Other than stating that obvious fact, not much can be said for the first experiment other than we proved Yeast is extremely important for making the Dough rise. Without the Yeast giving off Carbon Dioxide, the Dough wouldn’t rise. It would also be good to note that the Dough’s sticky material traps the Carbon Dioxide, causing the mound to rise.


For our Alcoholic Fermentation experiment, once again, my Hypothesis was right on the mark. The Fermentation caused by the Yeast created heat, warming up the tube. Also it turns the sugar into Alcohol and simply smelling the Test Tube, after the experiment, can also prove this as Alcohol has a very distinctive smell, easily recognised. My third observation of this experiment showed that Carbon Dioxide was given off, turning the Lime Water milky.

I cannot say I learned a lot from these two experiments but as my knowledge was solely based on Theory, doing it in practise helped to reassure what little doubts I had. Practical work is always good for testing Theory and I’m glad that we were allowed to take part in this.

Written by Thomas Grome

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