190 BUTTER-MAKING. 
stances are. They are evidently volatile, ether-like compounds, 
which are produced by bacterial growth during the ripening 
process. Few years ago it was thought that these flavoring 
substances were due entirely to the oxidation process, and 
that in order to get these flavors in butter it was necessary to 
expose the cream to pure air during the ripening. It has now 
been proved that air might be excluded from the cream-vat, 
and still good results be obtained. This does not, however, 
demonstrate that oxygen is not essential for the best results in 
cream-ripening. All cream contains more or less oxygen in 
solution. It has been thought that the oxygen that cream 
holds in solution may favor the growth of the desirable germs 
in cream, and that as soon as this has been utilized, conditions 
may become unfavorable for the desirable germs and favorable 
for the undesirable germs. 
Practically, all the investigators agree that the flavor and 
aroma substances which are characteristic of butter and which 
are developed in ripening cream, are due to bacterial growth, 
and that the germs producing lactic acid are the most desirable 
ones. We quote the following instances to show what effect 
some species of bacteria may have upon the quality of butter, 
when present in the cream: 
Number. Species Used for Starter. sear ent Pisyon, Peete 
1 Bacterium lactarti...........- 39 $.20 
2 Bacillus subtillis............ 31 14 
These two samples of butter were made from the same 
kind of cream which was pasteurized and inoculated with 
starters from the different germs as indicated in the table.* 
The butter ripened with Bacillus subtillis sold for 6 cents 
per pound less than the other, a difference of nearly one-third 
in value, due to the character of fermentation in the cream 
during ripening. Therefore in developing the proper fiavors in 
* Bul. 40, Iowa Experiment Station. 
