THE USEFUL MICROBES 
47 
is called an artificial starter. To use such an 
artificial starter successfully, the place where 
the butter is made, and the containers used, 
must be kept extremely clean, so that no other 
kind of microbe, besides the one especially put 
in the cream, will produce the desired action. 
Microbes play an even larger part in the 
making of cheese than in the making of butter. 
When cheese is made, the milk is allowed to 
sour and then a microbe growth, known as 
rennet, is added, which separates the curds from 
the liquid. The curd is then ripened by the 
action of another set of microbes, which grow 
in it in enormous numbers. The kind of 
cheese that results, and its flavor, depends on 
what sort of microbes are used. Most of these 
microbes belong to a class known as molds, 
and several different kinds of molds are often 
used in the making of a single kind of cheese. 
The green spots found in Roquefort cheese are 
one kind, and give it its sharp flavor. Two 
kinds of molds are used in making Camembert 
cheese. One forms the feltdike surface on the 
How do they 
help to ma\e 
cheese? 
