Investigation of the Role of Yeast and Bacteria in the Fermentation of Flour and Milk

Abstract

This investigation explores how microorganisms like yeast and bacteria aid in the fermentation process of flour and milk. The experiment helps students observe the transformation caused by microbial activity and understand its importance in food processing.

Introduction

Fermentation is a metabolic process where microbes convert sugars into gases, acids, or alcohol. Yeast plays a key role in the fermentation of flour during bread making, while bacteria, particularly lactic acid bacteria, are essential for milk fermentation in yogurt and cheese production.

Procedure

1. Take two clean jars: one with a flour-water mixture and the other with milk.
2. Add yeast to the flour mixture and lactic acid bacteria (from yogurt) to the milk.
3. Cover both jars with a cloth and leave them at room temperature for 24–48 hours.
4. Observe the smell, texture, and formation of bubbles or curd.

Observation and Calculation

Flour + Yeast: Dough rises, smells slightly alcoholic or sour, and shows bubbles indicating gas production (CO₂).

Milk + Bacteria: Milk thickens into curd with a sour aroma, confirming lactic acid fermentation.

Conclusion: Yeast ferments sugars in flour to produce CO₂ and alcohol; bacteria convert lactose in milk to lactic acid, preserving and souring the milk.

20 Short Questions with Answers

1. What is fermentation?
   Answer: Fermentation is a biological process in which microorganisms convert sugars into gases, acids, or alcohol.
2. Name one microorganism involved in flour fermentation.
   Answer: Yeast.
3. Which bacteria are used in milk fermentation?
   Answer: Lactic acid bacteria.
4. What gas is produced by yeast?
   Answer: Carbon dioxide.
5. What is the sour product of milk called?
   Answer: Curd or yogurt.
6. Why does dough rise during fermentation?
   Answer: Because of the carbon dioxide gas produced by yeast.
7. What is the role of lactic acid bacteria in milk?
   Answer: They convert lactose into lactic acid, causing the milk to sour and thicken.
8. How long was the flour mixture left to ferment?
   Answer: For 24–48 hours.
9. What change occurs in the smell of milk after fermentation?
   Answer: It develops a sour smell.
10. What conditions are required for fermentation?
    Answer: Warm temperature, moisture, and absence of air (anaerobic conditions).
11. Is oxygen necessary for fermentation?
    Answer: No, fermentation usually occurs in anaerobic conditions.
12. What is curd scientifically known as?
    Answer: Coagulated milk or yogurt (depending on the process).
13. What sugar does yeast feed on in flour?
    Answer: Glucose (and other simple sugars present in the flour).
14. What sugar does bacteria convert in milk?
    Answer: Lactose.
15. Is the fermentation process chemical or physical?
    Answer: Chemical.
16. Can fermentation occur in cold temperatures?
    Answer: It slows down significantly; optimal fermentation requires warm temperatures.
17. Why is fermentation important in food processing?
    Answer: It helps preserve food, improve flavor, and increase nutritional value.
18. Which vitamin is sometimes produced during fermentation?
    Answer: Vitamin B12 and other B-complex vitamins.
19. Does yeast cause milk to ferment?
    Answer: No, bacteria cause milk to ferment, not yeast.
20. What change in texture is observed in fermented milk?
    Answer: It thickens and forms a gel-like structure.

5 Multiple Choice Questions (MCQs)

1. What does yeast produce during fermentation of flour?
   Ⓐ Oxygen Ⓑ Carbon dioxide Ⓒ Hydrogen Ⓓ Nitrogen
   Answer: Ⓑ Carbon dioxide
2. What is formed when milk is fermented by bacteria?
   Ⓐ Yogurt Ⓑ Butter Ⓒ Water Ⓓ Vinegar
   Answer: Ⓐ Yogurt
3. Which of the following causes the dough to rise?
   Ⓐ Alcohol Ⓑ Lactic acid Ⓒ Carbon dioxide Ⓓ Water
   Answer: Ⓒ Carbon dioxide
4. Which microorganism is used in fermenting milk?
   Ⓐ Yeast Ⓑ Lactic acid bacteria Ⓒ Fungi Ⓓ Amoeba
   Answer: Ⓑ Lactic acid bacteria
5. What is the byproduct of milk fermentation that makes it sour?
   Ⓐ Ethanol Ⓑ Acetic acid Ⓒ Lactic acid Ⓓ Citric acid
   Answer: Ⓒ Lactic acid