DECOMPOSITION OF ORGANIC COMPOUND 235 



make a marked difference in the texture and flavor of the 

 product. 



7. Time of ripening. Some cheeses require a very much 

 longer period of time for their complete ripening than do 

 others. 



8. The organisms present and active in the ripening 

 process. The kinds of microorganisms present and active 

 will depend very largely upon the factors already enumer- 

 ated. Perhaps it may be emphasized that all the preceding 

 conditions are attempts to vary the conditions under which 

 microorganisms will be active and consequently vary the 

 type and proportion of products developed. In some cases 

 particular microorganisms will be active and consequently 

 vary the type and proportion of products developed. In 

 other cases, certain microorganisms are intentionally intro- 

 duced. Usually they are present in the material and there 

 is no need of special inoculation. 



Types of Cheeses. Cheeses may be differentiated into 

 acid curd cheeses and rennet curd cheeses; the latter, in 

 turn, into the hard cheeses and soft cheeses. 



Acid Curd Cheeses. Acid curd cheeses are prepared by 

 allowing the milk, usually whole milk, to sour spontaneously 

 or after the introduction of a suitable starter. When the 

 acidity has reached a suitable point the material is heated, 

 whereupon the whey separates out. The curd is then 

 made into balls or cakes and sometimes mixed with cream 

 or butter before use. The so-called Dutch cheeses and 

 cottage cheeses prepared in the household are of this type. 

 They are usually not ripened before they are used. By a 

 special process, sour curd cheeses are ripened in some of the 

 Scandanavian countries and a peculiar type of cheese pro- 

 duced. Ordinarily acid curd cheeses are not held for very 

 long periods of time, inasmuch as the yeasts and molds soon 

 make the cheese unfit for use. 



Rennet Curd Cheeses. Of the many types of rennet curd 



