A text-book of cooking

The following experiments show the growth of bacteria on food : THE PRINCIPLES OF PRESERVING FOOD 293 Experiment 90 : Growth of Bacteria. — Into test tubes put one of the following foods: (1) bit of uncooked meat; (2) small quantity of egg ; (3) piece of bread ; (4) crushed peas or beans ; (6) sugar or syrup. Add a little water to each tube. Set aside in a warm place. After several days, examine. What change in appearance dp you note ? What has caused the foods to spoil ? Experiment 91 : Effect of Boiling on the Growth of Bacteria. — Place a little chopped meat in two test tubes. Add lukewarm water to each. Boil the contents of one of the tubes for several minutes. Set both aside. After 24 hours, examine. What difference is there in the condition of the meat in each tube ? Explain this difference. From the result of this Experiment draw conclusions regarding the boiling of food to prevent spoiling. Experiment 92 : Effect of Preservatives on the Growth of Bacteria. — Beat slightly an egg-white. Add to it J cupful of water. Pour a little of the diluted egg-white into four test tubes. To three of the test tubes add one of the following: (1) salt; (2) sugar; (3) vinegar. Put all of. the tubes in a warm place. After several days, examine. What is the condition of the egg-white in each tube ? Explain. Draw inferences regarding the use of " safe " preservatives to prevent foods from spoiling. The Principles of Preserving Food. — Food may be preserved by opposing the growth of microorganisms or by destroying them. Low temperatures, certain preservatives, and drying destroy microorganisms or retard their growth. Drying is effective in preserving such foods as fruits, certain vegetables, fish, and meats. The drying of fruit and vegetables may be done in the home. This process of food preservation is practical only when there is an excessive supply of fruit or vegetables in the orchard or garden. It is usually not economy to buy fruits or vegetables at market for home-drying. Substances known as preservatives are used in food preservation. Some of these are harmless, as sugar, salt, vinegar, and spices. Others are harmful, as formaldehyde, salicylic, benzoic, and sulphurous acids, with their related compounds. Saltpeter and smoke are also preservatives. There is some doubt concerning the harmlessness of these latter preserving agents. Foods preserved with harmful materials should never be used. Good food materials can be preserved without the use of harmful preservatives. The destruction of microorganisms by heat is the basic principle of preserving much food, especially fruit. This process is called sterilization. In order to preserve fruits it is necessary not only to sterilize them, but to place them in sterilized cans and to seal these to exclude the air from them. It is necessary, also, to sterilize all utensils which come in contact with the foods in the processes of cooking and sealing. If canned fruits do not "keep," some microorganisms either in the fruit, on the can, or on the utensils used in canning, have not been destroyed, or the can has not been securely sealed. A perfectly sterilized and securely sealed jar of fruit ivill keep indefinitely. Slight flaws in the can which were not detected at the time of sealing may cause the spoiling of carefully canned fruit. In the preservation of fruit, one should make every effort to secure sound fruit, perfect jars, and good rubbers, and to have the fruit and utensils perfectly sterilized, and the jars securely sealed. Failure to accomplish these ends may result in much loss of materials and time. Explain why boiled milk keeps sweet for a longer time than uncooked milk. Why do foods need to be sealed to preserve them ? Why does cooked meat " keep " longer than uncooked meat ? STERILIZATION WITH LITTLE SUGAR 295 LESSON CI