286 SCIENCE AND PRACTICE OF CHEESE-MAKING 



organisms or of chemical agents. We thus have two 

 general kinds of ferments, (i) organized ferments 

 and (2) unorganized ferments, known also as chem- 

 ical ferments or enzyms. In the illustrations given 

 above, the ferments are ( i ) lactic acid organisms and 

 (2) rennet ferment; in one case the organic matter 

 ohanged is milk-sugar; in the other, milk-casein. 

 Organized ferments are living micro-organisms, 

 capable, as a result of their growth, of causing fer- 

 mentations. Unorganized ferments are chemical sub- 

 stances, or ferments without life, capable of causing 

 marked changes in many complex organic compounds, 

 the enzyms themselves undergoing little or no change. 



General characteristics of ferments. — Ferments 

 possess certain general characteristics in common, 

 among which may be mentioned the following: (i) 

 A very small amount of ferment is capable of pro- 

 ducing very great changes. (2) They are all de- 

 pendent upon temperature as a condition of activity. 

 They cease to act at low and also at high tempera- 

 tures. Most of them find the temperature that is 

 best suited to» their greatest activity between 80° and 

 100° F. (3) Ferments are destroyed by heat, the 

 temperature of boiling water, in most cases, com- 

 pletely destroying their power to act. Their activity 

 is checked by low temperatures, but, when again 

 warmed, they renew their activity. (4) The action 

 of ferments is checked or prevented by many sub- 

 stances. (5) When the products formed by ferments 

 accumulate in certain amounts, the ferment action 

 usually stops. (6) All ferments are closely con- 

 nected with living processes. 



Organized ferments, or living micro-organisms 

 capable of causing fermentations, are divided into 



