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066 fermentation (lactic acid)

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This document describes an experiment to demonstrate lactic acid fermentation in milk. Students will observe two cups of milk, one warm and one hot, each with added curd starter culture. Over 48 hours, they will record observations of color, smell, and appearance to see how bacteria convert milk sugar to lactic acid, causing curds to form. The experiment aims to show how temperature affects the rate of fermentation and curd formation, and to illustrate the beneficial role of microbes in food production.

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066 FERMENTATION (LACTIC ACID) To demonstrate how bacteria convert milk sugar to lactic acid to set curd MATERIALS REQUIRED Two Cups Milk Burner / Stove (to be done under adult supervision) Milk
Take 2 cups of boiled milk Cup A with slightly warm milk and Cup B with bubbling hot milk (this should be done by the adult). Add about a quarter teaspoon of curd to both cups and stir the curd gently but well into the milk. Cover and place both cups inside a cupboard or away from the sun Note the time when the experiment was started (it is preferable to start the experiment in the morning) Curd Curd Milk Milk A B warm milk hot milk
Observe and record from both cups (A & B): Colour Smell Change in appearance (bumps on the surface, bubbles, etc.) The recording of observations should be done at least for 48 hrs: time '0' start of the experiment (morning); after 4 hours in the afternoon; another 4 hours later in the evening before school closes; 2nd day morning, afternoon, evening, and on 3rd day morning A B warm milk hot milk
THROUGH THIS EXPERIMENT: Understand the principles of lactic acid fermentation by bacteria (mainly Lactobacillus sp.) from a simple daily activity in any Indian household. Understand if it is different from alcohol fermentation that you observe in the balloon experiment with sugar and yeast / bread. If it is different why is it different? What is the role of temperature in the process of lactic acid fermentation? Is there a difference in the curd formation in the two cups? If yes, why is there a difference? Does temperature affect the milk or the microbial action of fermentation? Learn that not all microorganisms cause disease! Many of them help in producing food and are beneficial to health.

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066 fermentation (lactic acid)

  • 1. 066 FERMENTATION (LACTIC ACID) To demonstrate how bacteria convert milk sugar to lactic acid to set curd MATERIALS REQUIRED Two Cups Milk Burner / Stove (to be done under adult supervision) Milk
  • 2. Take 2 cups of boiled milk Cup A with slightly warm milk and Cup B with bubbling hot milk (this should be done by the adult). Add about a quarter teaspoon of curd to both cups and stir the curd gently but well into the milk. Cover and place both cups inside a cupboard or away from the sun Note the time when the experiment was started (it is preferable to start the experiment in the morning) Curd Curd Milk Milk A B warm milk hot milk
  • 3. Observe and record from both cups (A & B): Colour Smell Change in appearance (bumps on the surface, bubbles, etc.) The recording of observations should be done at least for 48 hrs: time '0' start of the experiment (morning); after 4 hours in the afternoon; another 4 hours later in the evening before school closes; 2nd day morning, afternoon, evening, and on 3rd day morning A B warm milk hot milk
  • 4. THROUGH THIS EXPERIMENT: Understand the principles of lactic acid fermentation by bacteria (mainly Lactobacillus sp.) from a simple daily activity in any Indian household. Understand if it is different from alcohol fermentation that you observe in the balloon experiment with sugar and yeast / bread. If it is different why is it different? What is the role of temperature in the process of lactic acid fermentation? Is there a difference in the curd formation in the two cups? If yes, why is there a difference? Does temperature affect the milk or the microbial action of fermentation? Learn that not all microorganisms cause disease! Many of them help in producing food and are beneficial to health.