BACTERIA IN CREAM AND BUTTER 515 



to obtain definite proof of this, owing to the uncertainty of scores 

 in butter tests. But the fact that all good dairies use them is sufficient 

 testimony to their value in improving the general quality of the 

 butter. 



"4. They are the best means of remedying butter faults. Every 

 creamery has experiences of deterioration in the flavor of the butter 

 without any visible cause. Such troubles are known to be due com- 

 monly to the growth of unusual and undesirable bacteria in the cream. 

 When they are discovered the sterilizing of the dairy utensils and 

 the use of a larger quantity of vigorous starter will generally remedy 

 the trouble at once. Moreover, the constant use of a starter goes a 

 long way toward preventing these ''faults." It is doubtful whether the 

 use of starters produces a butter of a character superior to the best 

 butter made without them. Indeed, some think that it is not quite 

 ^qual to the best butter made without starters. But the uniformly 

 high grade of culture butter is admitted, and the greater satisfaction 

 in being able to control the process has caused the wide adoption of 

 starters among buttermakers." 



Bacteria in Cream and Butter. The ripening of the cream is due to 

 bacterial growth, chiefly lactic-acid bacteria, with the formation of 

 lactic acid from lactose. The proper ripening of the cream, however, 

 cannot be brought about by simply adding to it a certain amount of 

 lactic acid. This shows that a variety of bacterial enzymes are 

 active in ripening cream so that it will be in the best shape for butter- 

 making; this is generally the case when the acidity present is equal 

 to 0.5 to 0.65 per cent. An enormous increase of bacteria occurs in 

 cream during the changes which lead to ripening. From 2,000,000 to 

 3,000,000 bacteria per c.c. may have been present in the sweet cream, 

 and when it is ready or ripe for butter-making the number may have 

 increased to several hundred million per c.c. and even to 2,000,000,000. 

 The ripening is best allowed to continue at 65 F., because at that 

 temperature the danger of development of undesirable butter-spoiling 

 bacteria is much less than at higher temperatures. The growth of 

 bacteria in ripening cream is generally stopped by churning ; many of 

 them are removed with the buttermilk and more with the subsequent 

 washing and kneading of the butter. While butter is being kept 

 the number of bacteria rapidly decreases, particularly in salted butter. 

 Conn gives the following examples : Number of bacteria present per 

 gram of butter two hours old, 54,000,000; one day old, 26,000,000; 

 four days old, 2,000,000; thirty days old, 300,000. There are, however, 

 some bacteria present even in very old butter. In order to protect 

 butter against subsequent changes it must be kept at a low tem- 

 perature and protected against light and air. If this is not done it 

 will soon become rancid, i. e., some of the butter fat is decomposed 

 and changed into butyric acid, a fermentative process due to certain 

 bacteria and their special enzyme. 



