CAUSES OF RIPENING CHANGES 371 



only after the lapse of about one year, a*id the increase 

 is so very slow, that even after two years, only minute 

 amounts are present. From these results, it apfpears 

 that while galactase performs important work in the 

 ripening of cheese, it cannot be the chief factor in this 

 process, because its action produces amino acids only 

 very slowly, and ammonia practically not at all within 

 the normal lifetime of cheddar cheese. 



One of the properties of galactase is its sensitive- 

 ness to acids. In milk containing 0.15 per cent of 

 hydrochloric acid, the galactase is much less active 

 than in milk containing less acid. In the work done 

 at the New York experiment station, the addition of 

 as much as 0.2 per cent of acid materially increased 

 the amount of soluble protein compounds in cheese. 

 Thus, cheese made with no acid had not ripened at all 

 in 3 months, while cheese made with acid under con- 

 ditions otherwise the same, contained 32.37 per cent 

 of its nitrogen in soluble form in 3 months. This fact 

 also is not consistent with the belief that galactase 

 is the chief agency in the process of cheese-ripening. 



ACTION OF MICRO-ORGANISMS IN 

 CHEESE-RIPENING 



We come now to a consideration of the fourth and 

 last agency which has been assigned as one of the 

 causes of the chemical changes in the ripening of ched- 

 dar cheese, micro-organisms. Although we discuss 

 this subject last, it was, in point of time, the first to 

 be studied. When the subject of cheese-ripening was 

 first taken up for serious study, it was thought that 

 the whole process was due to the action of bacteria, 

 and all efforts were confined to this single line of 



