518 BACTERIA IN. BUTTER AND CHEESE-MAKING 



has decreased and after some ammonia has been formed, hay bacilli 

 and certain hyphomycetes become more active, they secrete pepton- 

 izing enzymes, and the ripening process makes more rapid progress. 

 The lactose fermentation first occurring in cheese is a most impor- 

 tant process, which prevents true putrefactive changes and prepares 

 the field for a ripening of the proper kind. Saccharomyces, oidia 

 and hyphomycetes probably play an important role in the ripening of 

 cheese and in giving it the proper flavor. Saccharomyces very likely 

 produce esters during the acid formation; oidia and hyphomycetes 

 neutralize the acids and give the peptonizing bacteria a chance to 

 multiply and to produce their proteolytic enzyme." It has been shown 

 by Conn and others that Camembert cheese owes its ripening and its 

 flavor and taste mainly to the presence of Penicillium candidum and 

 Penicillium glaucum, while Roquefort cheese owes its properties to 

 the presence of a variety of Penicillium glaucum(Penicillium roqueforti 

 or Penicillium aromaticum casei). The bacteria in ripening cheese, 

 according to Conn, for a number of days, sometimes for several weeks, 

 increase in numbers. After this they decrease until when the cheese 

 is fully ripened they are very few compared to their number at certain 

 stages of the ripening. An examination showed in fresh cheese 

 6,600,000 bacteria per gram; when four days old, 51,000,000 per gram, 

 and when four months old, 1,000,000 per gram. Faults in cheese, 

 such as a gassy condition, swelling, undesirable flavor, have been shown 

 to be due to undesirable bacteria or torulas. To prevent such faults 

 Conn recommends cleanliness, a vigorous lactic-acid starter for the 

 souring of the milk, and a temperature of 60 F., which is not favorable 

 to those organisms, generally responsible for the faults of cheese. 



QUESTIONS 



1. How can the cream be separated from the remainder of the milk? 



2. What causes the ripening of the cream? 



3. How much acidity does ripe cream contain ? 



4. How can the acidity be ascertained ? 



5. How can the ripening be produced by the addition of lactic acid ? 



6. What is a natural starter? 



7. What is an artificial starter? 



8. What microorganism is more particularly the cause of the ripening of the 

 cream? 



9. What is meant by aroma microorganisms ? 



10. Why is their use sometimes dangerous? 



11. Discuss the advantages of using pasteurized cream for butter-making. 



12. What is the composition of buttermilk? 



13. What is meant by the building up of the starter? 



14. WTiat are the bacterial contents of sweet cream and of ripe (sour) cream 



15. Discuss the decrease in bacterial content during butter-making and in the 

 butter after its preparation. 



16. What is rancid butter; what causes its production ? 



17. What are the proteids contained in milk? 



18. How is coagulation of milk brought about? 



19. What is lab-enzyme or rennet? 



20. How can it be obtained ? 



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