Yeast Growth

Grade Level: 5th - 8th; Type: Cooking Science

To find out how much yeast can cause bread to rise.

The purpose of this experiment is to measure the growth of bread dough and find out how long it takes for the dough to stop rising.

• Why does bread rise?
• What kind of yeast is added to bread to make it rise?
• Is this the same type of yeast that is added to other foods?
• What is a fungus?
• How is a fungus like an animal?
• How is a fungus like a plant?
• What alcohol content will cause yeast to die?

An ingredient in many common foods, yeast is a single celled fungus that feeds on sugars. When mixed with bread flour and warm water, the yeast goes to work consuming sugars that are naturally contained in the flour. As a byproduct of its digestion, yeast releases carbon dioxide and alcohol. The carbon dioxide, in the form of bubbles, disperses throughout the dough and makes the bread rise. While bread does not contained noticeable amounts of alcohol, this waste product of yeast is the way that alcoholic beverages, such as beer and wine are prepared. Many recipes recommend that the baker allow the bread to rise for a few hours. After that time, most of the yeast in the dough has lived out its lifespan and does not create more carbon dioxide or alcohol.

• Baker’s yeast
• Flour
• Salt
• Sugar
• Olive oil
• Water
• Large bowls
• Cloth towels
• A wooden spoon
• Measuring tape
• Scale
• Calculator

1. Place ½ tea spoon of dry baker’s yeast in a bowl with 2 ½ cups of warm water.

2. Stir these ingredients rigorously.

3. Wait ten minutes. If the mixture starts to bubble, the yeast is active and can be made into bread. If the mixture does not bubble, the yeast is dead and you will need to start over with a new packet.

4. Mix 1 tablespoon of salt into the water.

5. Mix about 6 cups of bread flour into the water.

6. Knead for twenty minutes, adding up to another cup of flour if the mixture is too wet to stay together.

7. Form the dough into a ball.

8. Place the ball on the counter.

9. With the dough in a ball (it will not be exactly spherical), measure the distance from the center of the ball to the outer edge. You will need to do your best to measure where the center is using the top of the dough to where the outer edge is at the center of the dough (measured from the table up). Do not measure on an arc along the outer edge of the dough, rather, measure a line parallel to the plane of the table. This will be the length variable in the equation.

10. Measure the distance from the center of the ball to the outer edge 90 degrees from your previous measurement. This will be the width variable in the equation.

11. Measure the distance from the center of the ball to the table. This will be the depth variable in the equation.

12. Calculate the volume of the ball by using the following formula: (4/3)(π)(length)(width)(height). (This formula is a variation of the formula to find the volume of a sphere and assumes that your shape is not exactly spherical.)

13. Take the mass of the dough.

14. Pour one tablespoon of olive oil into a large bowl and coat the bottom and the sides.

15. Place the dough in the bowl.

16. Get a kitchen towel damp with water.

17. Place the towel over the bowl.

18. Place the bowl in a cool dark cupboard or room where it will not be exposed to a draft.

19. Wait 30 minutes.

20. Repeat steps 7-13.

21. Wait 1 hour.

22. Repeat steps 7-13.

23. Wait 2 hours.

24. Repeat steps 7-13.

25. Wait 4 hours.

26. Repeat steps 7-13.

27. Wait overnight.

28. Repeat steps 7-13.

29. Wait 8 hours.

30. Repeat steps 7-13.

31. Wait overnight.

32. Repeat steps 7-13.

33. Wait 24 hours.

34. Repeat steps 7-13.

35. If you have time, see how the dough fares over the next week, taking daily measurements.

Terms/Concepts: yeast; byproduct; alcohol; sugar; carbon dioxide

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