PREPARING AND PRESERVING FOOD 



87 



4. You may find the following new words in this 



study: 



fermentation the production of carbon dioxide and al- 

 cohol by the action of bacteria or yeast on sugar. 



spore the reproducing body of plants which have no 

 flowers, such as mosses, ferns, and molds. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 



Experiment 58. What happens to a potato when it is 

 cooked? 



Bring two potatoes to class. Pare one of them and cut 

 a thin slice from it. Place it on a glass slide and look at it 

 through a compound microscope. Can you see grains of 

 starch within the cells? 



Make a drawing of their appearance in your notebook. 



Place a few drops of iodine solution on the freshly pared 

 potato. 



What happens? 



Pare the second potato. Put- it into boiling water and 

 allow it to boil for nearly a half hour. Jab a fork into it 

 occasionally. When it is soft, remove it from the boiling 

 water and examine it carefully. Place a few drops of iodine 

 solution on a slice of the boiled potato and examine it under 

 the microscope. 



In your notebook 1 record the notes of this experiment 

 and answer the questions. 



How did the boiling water affect the starch grains of the 

 potato ? 



Was it easier to apply the iodine test after the potato 

 was boiled? 



Why do we cook vegetables before eating them? 



Experiment 59. What is yeast? 



Secure a yeast cake. Place a small part of it in a solution 

 of sugar and water and allow it to stand in a warm room 

 for a short time. By means of a medicine dropper transfer 

 a drop of the yeast solution to a glass slide and examine 

 it under the high power of a compound microscope. 



Can you see any of the yeast cells reproducing? How 

 do they reproduce? Record the notes of this experiment in 

 your notebook 2 with a drawing of what you observe. Com- 

 pare what you observe with Figure 129. 



Experiment 60. How do yeast plants affect sugar? 



Obtain a flask, a test tube, a one-hole rubber stopper, 

 and some glass tubing. Set up the apparatus as shown in 

 Figure 127. Make a solution of molasses in water, using 

 ten parts of water to one 

 part of molasses. Dis- 

 solve about half of a 

 fresh yeast cake in a small 

 quantity of warm water 

 and mix with the solution 

 of molasses. Pour the mix- 

 ture into the flask. Put 

 limewater into the test 

 tube. 3 In about a half hour 

 examine the apparatus and 

 notice what is happening. 



FIG. 127 



1 See workbook, p. 31. 

 ' See workbook, p. 32. 

 ' See directions for making limewater, footnote, p. 62. 



In your notebook 4 record the notes of this experiment and 

 complete the following statements. 



Bubbles of gas formed in the flask. As the bubbles passed 



through the limewater, the limewater became . The 



name of the gas formed is . 



As the yeast plants grow they feed upon which is 



split into and 



Why is yeast used in baking bread? 



Experiment 61. What are molds and how do they 

 live? 



Secure four wide-mouthed glass jars and four slices 

 of bread. Expose the bread to the air for about an hour. 

 Label the jars 1, 2, 3, 4. 



a. Moisten one slice of bread, put it in jar 1, cover the 

 jar, and keep it in a warm, dark place. 



b. Moisten another slice of bread, put it in jar 2, cover 

 the jar, keep it in strong sunlight. 



c. Moisten another slice of bread, put it in jar 3, cover 

 the jar, and keep it in a dark, cold place, preferably a re- 

 frigerator. 



d. Put the dry piece of bread in jar 4, cover it, and keep 

 it in a warm, dark place. 



Notice the changes that appear from day to day on the 

 four slices of bread and keep a record for about a week. 

 Examine the mold with a magnifying glass. 



In your notebook 5 record the notes of this experiment and 

 answer the questions. 



Does mold grow better in a warm or cold atmosphere? 

 Does mold require water for growth? Does sunlight help 

 or hinder mold in growing? Were different colors present 

 on the bread? What caused them? Under what conditions 

 should food be kept to prevent molding? 



Experiment 62. From where do bacteria that cause 

 food to spoil come ? 



Thoroughly wash a potato and boil it for fifteen minutes. 

 Cut it into thick slices with a knife that has been sterilized 

 in boiling water or a flame. Sterilize several saucers by 

 placing them in boiling water. With the sterilized knife 

 place a slice of potato on a saucer and let it be exposed 

 to the atmosphere for an hour. Cover it with a sterilized 

 glass and keep it in a warm place for a week. 



Place another slice of potato on a saucer, rub your fingers 

 over it, cover it with a sterilized glass, and set aside in a 

 warm place. 



Watch the development of bacteria colonies for a week. 

 Some molds may also appear. Why? 



If a microscope is available, smear some bacteria on a 

 slide and look at them with the high-powered lens. Try 

 to identify different kinds of bacteria. 



In your notebook 6 record your observations and results, 

 make drawings, answer the questions, and complete the 

 statements. 



Are bacteria in the air? Are bacteria on our hands? What 

 happens to bacteria when dishes are boiled in water? What 

 causes milk to sour? 



Bacteria are classified according to their shape. What 

 are rod-shaped forms called? Spherical-shaped forms? 

 Spiral-shaped forms? 



4 See workbook, p. 32. 



5 See workbook, p. 33. 

 * See .workbook, p. 33. 



