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 \^'as 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 imdesirable 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 foflowing instances to show what effect 

 some species of bacteria may have upon the quality of butter, 

 when present in the cream: 



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 subtilHs 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 flavors in 



* Bui. 40, Iowa Experiment Station. 



