Mrs. Pfahnl’s BioA Lab: Fermentation 2 Yeast Dough

Yeast is an eukaryote. It is a single cell fungi. Bacteria is a prokaryote.

The products from yeast fermentation are carbon dioxide and ethanol. This is why using store bought yeast you can make bread without sour taste. The carbon dioxide in the dough causes the volume to rise.

Sourdough is fermented by a mixture of bacteria and acid tolerable yeast. Similar to bacteria making yogurt, lactatic acid is one of the byproducts. That is why it tastes sour. It takes longer time for yeast in sourdough to produce carbon dioxide and ethanol.

Purpose:

Observe yeast fermentation process.

Materials:

1. Commercially available yeast product within expiration date

2. All purpose flour or bread flour

3. water

4. sugar

7. measurement tools

8. four dishwasher cleaned clear cups or jars at least 2 cups in volume

9. ruler

10. marker

Prodecure:

1. Label cups 1-4

2. Addd 0, ½teaspoon, 1 teaspoon and 2 teaspoon sugar into the 1-4 cups separately

3. Add half cup of room temperature water into each cup

4. Stir and make sure liquid becomes clear

5. Add ¼ teaspoon of yeast to each cup

6. Stir and let it sit for about 5 min (Activation of yeast activity, or waking up yeast from dormant state.)

7. Add half a cup of all purpose or bread flour to each cup and mix well

8. Let sit for a couple of min for the dough to settle to the bottom of the cup

9. Use a marker to mark the level

10. Keep it at room temperature and observe how the dough rise, mark the dough level on cups at 0.5h, 1h, 1.5h, 2h, 2.5h, 3 h, 3.5 h, 4h, 12 h

11. Use a ruler to mearure the height at each time point

12. Make a graph based on your data: X= time points, Y= rising dough level comparing with the original dough level. Use different color of simbol to represent different sugar level.

Grading:

1. Three Pictures 34%

2. Data and graph 33%

3. Presentation in Flipgrid 33%

Reference:

Bread Chemistry https://www.compoundchem.com/2016/01/13/bread/ Yeast and bread https://www.thekitchn.com/the-science-behind-yeast-and-how-it-makes-bread-rise-226483

Bread making https://www.theguardian.com/science/blog/2009/nov/26/science-breadmaking

Science of sourdough bread https://www.scientificamerican.com/article/the-science-of-sourdough-how-microbes-enabled-a-pandemic-pastime/

Global sourdough project http://robdunnlab.com/projects/sourdough/

Making sourdough bread https://www.theguardian.com/science/2020/may/23/the-science-of-making-sourdough-bread

Biology of sourdough https://www.discovermagazine.com/planet-earth/the-biology-of-sourdough

Intro video for sourdough https://www.youtube.com/watch?v=i6rdK_3_8Wg

Beginner sourdough video https://www.youtube.com/watch?v=BJEHsvW2J6M

Science behind sourdough https://www.youtube.com/watch?v=l_8UDwFETZo

UC Davis sourdough secretes https://www.youtube.com/watch?v=y5xOpss4j5E

CNBC repot on Sourdough bread https://www.youtube.com/watch?v=nX6SAH3w6UI

Mrs. Pfahnl’s experiment

1. four clean jars2. 1/2 teaspoon sugar into jar 2

3. 1 teaspoon sugar in jar 3, then 2 teaspoons sugar in jar 4
4. Add half cup water in each jar
5. sugar is not dissolved

6. use spoon to stir for sugar to dissolve 7. sugar dissolved in water completely

8. commercially available yeast
9. Add ¼ teaspoon yeast in each jar
10. Yeast floating on top11. Use spoon to stir and mix yeast into water

12. Add half cup of flour to each jar
13. use chopstick to stir and mix flour into liquid
14. Since the jar is almost full I transferred the content to a bigger jar.
15. Mark the original level of the mixture
16. Record time and temperature
17. At ½ hour, increased about 2 mm
18. At 1 hour, increased about 1 cm

19. At 2 hours it almost filled the whole jar.

20. At 11 hours, the level actually falling. 21. From 11 h to 25h they were left in 4 C refrigerator. Jar 1 and 2 fall to 1 h level, but 4 and 5 only dropped half a cm.