46 
WORLD OF INVISIBLE LIFE 
How do microbes 
help to ma\e 
butter? 
The part that microbes play in the making 
of butter is very important. On them depends 
the proper ripening of the cream, which is 
necessary for the making of a pleasant flavor. 
Butter made from sweet cream has the right 
taste, but cream that has been soured too long 
or by the wrong kind of microbe will have a 
bitter, or fishy, or soapy taste. Some of the 
lactic-acid microbes, which sour milk or cream, 
will give the butter a good taste, while others, 
closely related, will give it a bad taste. There 
are so many different lactic-acid microbes that 
the flavor of the butter varies in different dairies 
and in different countries. 
Because of these differences, scientists have 
spent much time in trying to find out just which 
of the lactic-acid microbes makes the best taste, 
and then growing them in the laboratory. 
They have selected the several kinds that will 
make good butter when they are put in cream 
that has been pasteurized to kill any other 
microbes that might cause trouble. The grow¬ 
ing of the pure microbe that is put in the cream 
