EXPERIMENT STATION BULLETINS. 261 



THE AERATION OF MILK* 

 CHARLES E. MARSHALL. 

 Special Bulletin 16 — Department of Bacteriology and Hygiene. 



Although practical aeration of milk may be traced back to an indefinite past, where 

 it is simply mentioned and recognized, there has never been any plausible explanation 

 or demonstration of the results claimed for it. Moreover, its application has always 

 been conspicuously limited until within very recent years, and so far as its value is 

 concerned at the present time, nothing has been satisfactorily established regarding 

 it, other than the belief that it eliminates animal odors and removes, to a certain 

 extent, tainted conditions of milk resulting either from physiological metabolism due 

 to ingestion of aromatic food substances or produced by the growth of saprophytic 

 bacteria in milk after the milk has left the udder of the cow. Even these animal 

 odors and taints have been more or less undefinable and immeasurable; only daily 

 practices in dairy operations have indicated and established beyond a doubt that both 

 of these are greatly lessened by proper aeration. 



Many other beliefs have been associated with or attributed to the process of 

 aeration, such as the production of more cheese and better cheese, the production 

 of more butter and better butter, the more rapid rising of the cream, the more rapid 

 churning of the cream, the better keeping qualities of the milk and butter — all of these 

 advantages have been assigned to aeration over the non-aeration of milk. 



I. REVIEW OF AERATION OF MILK. 



Studying from the standpoint of the dairyman, Willard (1), Arnold (2), Lewis (3), 

 Cooke "(4), Wing (5), Plumb (6), Dean (7), and the Danes (8) under Storch have 

 contributed to our knowledge of its application as it is at present practiced, but all 

 of their work fails to explain the process or to state what aeration is. They do not 

 throw light on why aeration may answer any of the above questions named. An attempt 

 is made to demonstrate whether butter made from aerated milk is better than butter 

 made from non-aerated milk, whether more cheese has been made from milk that has 

 been aerated than from milk that has not been aerated. By these methods, perhaps, 

 some valuable points have been settled, and still the future may change the character 

 of this work wholly, since it is true they have not answered the question, "What is 

 aeration?"' or more explicitly, "w r ere they really working with aerated milk or non- 

 aerated milk?" 



It seems pertinent at the start, that before we ran understand or explain aeration 

 of milk it is necessary we understand what aeration is, and we know whether we are 

 producing aerated milk or not. All the practical experiments executed have been with 

 aeration and non-aeration as they are known to us from present methods alone. The 

 difference between the two may not be so marked as suspected and for this reason 

 fail in producing the most noticeable effects. The starting point, non-aeration, must 

 be first established and from that our conclusions should, in a way, be drawn; that is, 

 we must determine any change in the carbon dioxide and oxygen content, with a 

 decrease in the former and an increase in the latter as a process whose final limitations 

 are not known or influences realized. 



It is regretted that the value of our present aerating methods cannot be stated 

 more exactly at this time, rather than depend xipon the virtually negative results 

 obtained by the individuals named in their endeavor to secure some practical explana- 

 tion through their practical experiments. We hope to make this our next task : for 



* Thesis presented for the degreee of Doctor of Philosophy, University of Michigan. 

 (1.) Willard's Practical Dairy Husbandry, 1871, p. 183. 

 C2.) Loc. cit. 



(3.) U. S. Agric. Report, 1874. p. 397. 

 (4.) Ver. Exp. Stat. Report. 1892, p. 123. 

 (5.) Cornell Exp. Stat., Bui. 39. 

 (6.) Purdue Exp. Stat., Bui. 44. 



(7.) College Reports (Guelph, Ont.), 1898, 1899. 1900. 1901. 



(8.) 48 de Beretning fra den Kgl. Veterinaer-og Landbokijskoles Laboratorium for Land- 

 konomiske Farsog. 



