BACTERIA IN THE INDUSTRIES. 1 07 



and in that state is scraped from the cylinders. Dry milk is a common in- 

 gredient of baby foods and invalid foods, and is also very extensively used 

 in the manufacture of chocolate creams. The condensed and dry milks do 

 not keep long in spite of the greatest care in manufacture. The containers 

 and milk must be thoroughly sterilized or pasteurized, and the cans must 

 not be opened until ready for use. Such preservatives as salicylic and boric 

 acid are sometimes added to condensed milk. 



It is known that sweet cream yields a very insipid, flavorless butter, 

 whereas cream which has " soured" for a few days yields a pleasant tasting 

 and pleasingly flavored butter, provided the desirable species or variety of 

 bacteria are present. If the souring is continued too long the flavor may 

 be hopelessly vitiated. In the past it was customary to add a small amount 

 of old cream, having a desirable flavor, to a new lot of cream. This mother 

 cream was designated the " starter." It contained the desirable cream- 

 ripening bacteria, mostly of the lactic acid variety. These old-time natural 

 starters are now largely replaced by starters, prepared in the laboratory 

 consisting of pure cultures of certain breeds or varieties of cream flavor, 

 producing germs of the lactic acid group. A proper regulation of the tem- 

 perature is very important in the ripening of cream (60 to 75 F.). It is 

 also necessary to pasteurize the cream before adding the bacterial starter 

 in order to prevent the development of microbes which might interfere with 

 the proper development of the starter microbes. Naturally the use of clean, 

 sterilized utensils and uniformity of methods are all-important, in order that 

 uniform results may be obtained. 



Cheese flavors are also due to bacterial action, but not wholly so, 

 as many of the higher fungi, as species of Penicillium (Camembert 

 Penicillium) and of Oidium (O. lactis) also play a very important part as 

 flavor producers. The Roquefort cheese owes its characteristic flavor, in 

 part at least, to a variety or form of Penicillium glaucum. The qualities and 

 properties of some Swiss and soft Belgian cheeses are largely due to Oidium 

 lactis. The ripening of hard cheeses (Cheddar, Edam, American, some 

 Swiss varieties, and others) is due exclusively to bacterial action. Cream, 

 butter and cheese are very prone to the attacks of objectionable bacteria and 

 moulds which cause very unpleasant flavors and bitter taste. 



It must also be borne in mind that cream, cheese and butter may carry 

 disease germs. Tubercle bacilli have been reported in these food articles, 

 but it has not been demonstrated that they are frequently present. Typhoid 

 infections have been traced to the use of cream, but no case of typhoid fever 

 has ever been definitely traced to eating butter or cheese. Of course, these 

 articles may become infected after manufacture and thus become a possible 

 means of spreading disease. 



