A laboratory manual of foods and cookery

91. - - Prepare butter from sweet cream. Prepare butter from an equal volume of sour cream. Compare resulting butter as to flavor, texture, and quantity. (Keep the buttermilk for Expts. 92 and 93.) MILK, CREAM, AND' BUTTER 85 92. - - a. Compare each buttermilk as to flavor and color. b. Use each in gingerbread. Is any perceptible difference noticed? 93. - - a. Reaction of milk. Test fresh milk with delicate litmus paper and record results for comparison with tests to be made later. b. Compare the behavior of the two buttermilks from Expt. 91 toward litmus paper with that just observed in the case of sweet milk and with each other. Is there any relation between the differ- ence here seen and that observed in making gingerbread (Expt. 92) ? Constituents of Milk 94. — a. The presence of water and fat in milk has been suffi- ciently demonstrated in the above experiments. b. If a platinum or quartz dish is available, a little of the milk may be dried and burned to determine whether it yields ash. 95. - - a. Test milk for protein by means of the biuret 1 and xantho- proteic 2 reactions. b. Try heating some of the fresh milk to boiling. Does it contain a protein coagulable by heat like that of egg-white (page 109) ? 96. - - Acidulate another portion of the milk with acetic acid or vinegar, warm gently, and compare with the preceding test. Filter through wet filter paper and save the nitrate. Apply the xantho- proteic reaction2 to the solid which remains on the filter paper. 97. - • Test a portion of the filtrate from Expt. 96 for the presence of sugar by means of the Fehling-Benedict test (page 13). What conclusion can be drawn from the result ? Do all sugars respond to this test ? 98. - - Apply the iodine test (page 13) both to a portion of the filtrate from Expt. 96 and to a separate portion of the whole milk. 1 Biuret Reaction. If a few .drops of copper sulphate solution are added to pro- tein, in solution, and then an excess of caustic potash added, a red to violet colora- tion is produced. 2 Xanthoproteic Reaction. When nitric acid is added to protein (either in solu- tion or in solid form) a yellow color is produced which, on the addition of ammonia, becomes bright orange. 86 LABORATORY MANUAL OF FOODS AND COOKERY What conclusions are justified as to the nature of the carbohydrate portion of milk? 99. — Heat milk in double boiler. Strain the heated milk through a damp cheesecloth and test again for the xanthoproteic reaction. 100. - - Prepare 4 junket custards, using i c. sweet milk and \ junket tablet dissolved in f tsp. cold water in each instance. Pro- ceed as follows : a. Add dissolved junket to cold milk. b. Add dissolved junket to warm milk. c. Add dissolved junket to milk and boil i minute. d. Add dissolved junket to cold milk. Allow a, b, and c to stand in room at room temperature. Put d in refrigerator. e. Compare results at end of 10 minutes. /. Which method has proven most satisfactory ? g. Why? h. What is junket ? 101. - - Prepare i qt. of junket according to the most successful method. After the mixture has stood for i hour, cut with a knife into small pieces. Note results. What is the yellowish liquid that appears ? 102. - - a. Strain mass prepared in Expt. 101 through wet cheese- cloth.