338 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



relative to the influence of metal salts on the flavor of butter. These 

 salts, even in the smallest traces, have a very marked effect on butter. 



Exact determination of the pises in butter have been made, and it 

 has been found that peiroptible decrease in oxygen takes place during 

 the storage period. This has an important bearing on the question 

 of oxidation during storage. 



Over 50 samples of butter have been analyzed in an attempt to 

 find means of detecting butter neutralized with lime and soda ash, 

 but so far this work has been unsuccessful. 



A simple test has been perfected for determination of fat in butter. 



Work on the manufacture of butter for storage has been com- 

 pleted. The results consistently show much higher keeping quality 

 in butter made from sweet pasteurized cream. This work includes 

 also the effect of storage temperatures. Results have been submitted 

 for publication. 



A new method of producing dairy cultures of exceptional virulence 

 has been successfully perfected. This work is of essential importance 

 in the manufacture of starters, etc. 



CHEESE INVESTIGATIONS. 



Swiss cheese. — In continuing the investigations regarding the 

 Swiss type of cheese much has been required in the way of working 

 out methods. By the use of some of these methods it has been pos- 

 sible to follow the bacteriological changes in Swiss cheese through 

 the entire ripening period. Several hundred cultures are being 

 studied in connection with this work, and a paper is being prepared 

 on the normal bacteria of Swiss cheese, giving the results. 



Much work has also been done on the gases that are found in Swiss 

 cheese. It has been found that normal cheese contains only carbon 

 dioxid and nitrogen, w^hile abnormal chese contains also hydrogen. 

 These results in detail have been published as Bulletin 151. Chem- 

 ical and bacteriological studies in this connection as made so far lead 

 us to believe that eventually it will be possible to control the ripening 

 of Swiss cheese entirely by the use of pure cultures. This field offers 

 fine opportunities for research. 



Cheddar cheese. — In connection with the cooperative work at the 

 Wisconsin Agricultural Experiment Station on the Cheddar type of 

 cheese it has been demonstrated for the first time that bacteria of the 

 Bacillus hnlgcn^ctis type grow in large numbers after the sugar has 

 been entirely fermented and lactic-acid bacteria have diminished. 

 Results of this work have been submitted for publication. A com- 

 parison has been made of the acid test and the rennet test for the 

 purpose of determining the condition of milk for cheese making, 

 with the result that it is found that wide variations may occur in 

 the bacterial content of different milks without appreciably affecting 

 the amount of acid, but there seems to be a close relation between the 

 time required for coagulation with rennet and the number of bacteria 

 present. 



Chemical w^ork on Cheddar cheese has been devoted largely to a 

 comparison of the acids, esters, and alcohols in cheese of poor and of 

 good flavor, with the object of throwing some light on the origin of 

 flavoring matter. Definite conclusions are not yet warranted. 



The work on manufacture of cheese from pasteurized milk has 

 been continued, with the result that a product uniform both as to 



