Butter

89. - Heat a teaspoon each of pure butter, renovated butter, and oleomargarine in separate tablespoons over a bunsen burner.

Note the manner in which each melts and the appearance after melting.

This is called the foam test for butter. Why should the butter boil quietly while the renovated butter and the oleomargarine sputter and crackle?

90. - Place a tablespoon of each of the three samples used in Expt. 89 in each of three small beakers containing four tablespoons of sweet milk. Heat the beakers until the fats are melted, then place them in cold water and while the fat is still melted stir each vigorously with a splint of wood. Note the form the pure and renovated butters take and contrast with the condition of the oleomargarine.

Buttermilk

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.)

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 difference 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 sufficiently 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 biuret1 and xanthoproteic 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 filtrate. Apply the xanthoproteic 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 protein, in solution, and then an excess of caustic potash added, a red to violet coloration is produced.

2 Xanthoproteic Reaction. When nitric acid is added to protein (either in solution or in solid form) a yellow color is produced which, on the addition of ammonia, becomes bright orange.

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 1 c. sweet milk and \ junket tablet dissolved in 3/4 tsp. cold water in each instance. Proceed as follows: a. Add dissolved junket to cold milk.

b. Add dissolved junket to warm milk.

c. Add dissolved junket to milk and boil 1 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.

f. Which method has proven most satisfactory ?

g. Why?

h. What is junket ?

101. - Prepare 1 qt. of junket according to the most successful method. After the mixture has stood for 1 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 cheesecloth.

b. Apply the following tests to residue and filtrate respectively :

Biuret, page 85

Coagulation on heating Xanthoproteic, page 85 Fehling-Benedict solution, page 13 c. What are your conclusions ?

Milk (Sour)

103. - Have ready milk which has been sour 1 day, 2 days, 3 days.

a. Test equal volumes of each with litmus paper.

b. Neutralize each with-a solution of baking soda, testing with litmus paper.

c. Note the amount of soda required in each instance.

104. - a. Heat equal portions of each specimen of sour milk in a double boiler.

b. Note the clotting which appears.

c. Which clots quickest and in largest quantity ?

d. To what is this due ?

105. - a. Add salt to each portion in double boiler in the proportion of 1/8 tsp. to 1 c. of sour milk.

b. Note the effect.

c. How do you explain the result ?

106. - Strain the clotted masses from Expt. 105 through wet cheesecloth and allow to hang undisturbed until filtrate no longer drips. Test as usual with :

Biuret, page 85 Xanthoproteic, page 85 Coagulation on heating Fehling-Benedict solution, page 13

107. - a. Compare the cheese obtained in Expt. 106 with that made from sweet milk.

b. Note the difference in consistency, texture, and flavor.

c. To what is this due?

108. - Test each specimen of sour milk with litmus paper.

a. Which turns the paper quickest ?

b. What acid is present in sour milk?

c. How does it originate ?

(Leach, Food Inspection and Analysis) d. With the litmus paper still in the milk, add sufficient baking soda to neutralize the acid. Is a physical or chemical change produced ?

e. What is the gas given off after the soda is added ? f. In what food products is this principle applied?

g. Test 1 c. of sour milk with litmus paper and determine how much soda it is necessary to add to neutralize the acid.

h. Take an average of the results of the class and compare with the amount usually given in cook books. How does it compare ?

109. - a. Test 1 c. of sweet milk with litmus and add sufficient vinegar to produce the same intensity of color as in 108, g.

b. Neutralize a part of this milk with soda.

c. Compare the amount of soda needed with 108, g.

d. Prepare gingerbread, using the milk in 108, g in one instance and that in 109, a in the second instance.

e. Compare the two products. Is one preferable to the other?

f. Repeat g and heat the milk until the curd separates out. Compare this curd with that of normally sour milk and also with the curd made with junket and sweet milk.

g. What are the noticeable differences and to what are they due?

h. What sources of sour milk and curd have we?