LABORATORY WORK IN DAIRY BACTERIOLOGY 307 



small quantity of the culture from the package into a water 

 blank, and, by thorough agitation, distribute evenly through the 

 water. From this inoculate litmus gelatin tubes, some with one, 

 some with two and some with three loopfuls of the diluted cul- 

 ture. Pour into Petri dishes, incubate at 70, and after three 

 days examine to see whether any bacteria can be found in the 

 plate except lactic germs. 



No. 66. Effect Upon Butter of Pasteurizing Cream. Divide 

 a lot of cream which is to be made into butter into two parts, 

 pasteurize one at a temperature of 155 for 15 minutes, leaving 

 the other without pasteurization. Add to each the same amount 

 of starter. Ripen in the usual way, churn and make into butter, 

 and compare the products, to see if any difference can be noted 

 between the butter from pasteurized and non-pasteurized cream. 



No. 67. The Effect of Different Bacteria on Butter. The fol- 

 lowing experiment can be performed only where conveniences 

 are at hand for churning small quantities of cream. Pasteurize 

 a considerable quantity of cream, as above described, and divide 

 into several lots, placing each in a separate vessel. Inoculate 

 each lot with a starter made from different species of bacteria, 

 which have been isolated during the laboratory experiments. 

 Allow the cream to ripen in the normal way for the usual length 

 of time, and churn into butter. Compare the texture, taste and 

 aroma of the butter obtained in the different experiments. 



No. 68. The Effect of Light Upon Butter. Place two lots of 

 butter, one in a bright light and one in the dark, and after sev- 

 eral days compare them as to appearance, smell and taste. 



No. 69. Ripening of Cream at Different Temperatures. Di- 

 vide some cream into three lots. Place the usual amount of 

 starter in the cream, and ripen one lot at 50, one at 65 and one 

 at 85. After proper ripeness has been reached (determined 

 by acid test), churn and compare the butter which is obtained, 

 unsalted, to detect any difference in flavor and aroma. 



*No. 70. Analysis of Bacteria in Cheese. Determine the num- 



