236 THE ARTIFICIAL SOURING OF CREAM. 



the way for the action of the acid generator. Sterilisation, or at 

 least Pasteurisation, would afford the best results, but as these 

 are generally difficult to effect in a reliable .manner, a method of 

 weakening the " wild " bacteria present, by cooling the cream down 

 to a low temperature and then quickly warming it up again to 

 i6-2o C., has to be resorted to. The acid generator is then 

 added and well incorporated by stirring, and the cream vat is left, 

 at about 15- 20 C., until the following day, by which time the 

 cream will be ripe for churning. 



If it be desired to cultivate the acid generator further, a small 

 portion is taken from the bulk before use and employed in the 

 same way as a pure culture. 



In spite of the adverse opinion of many practical men, the 

 possibility of producing good butter from Pasteurised, or even 

 sterilised cream, has been demonstrated by the researches reported 

 by P. SCHUPPAN (I.) ; and BENNO MARTIN Y (II.) has drawn 

 attention to the hygienic advantages attending such a method of 

 working. Finally, it was proved by POPP and BECKER (I.) in 

 1893, that butter prepared from sterilised cream keeps better than 

 that from Pasteurised cream, and far better than that from cream 

 which has not been heated at all. 



142. The Aroma of Butter. 



The results of Weigmann's researches up to the present 

 (according to a private communication) indicate that probably 

 only a single species though appearing as numerous varieties 

 of bacterium sets up the lactic fermentation now in question. 

 This organism is a coccus (described by W. STORCH (I.),) measur- 

 ing about i //. in diameter, and uniting to form chains. The 

 varieties (also called races) of this coccus, which, from the point 

 of view of the systematic botanist, do not differ sufficiently 

 to be classified as separate species, generally exhibit one or 

 other of the following good qualities : they either give rise to a 

 powerful aroma, which imparts a very fine flavour to the butter, 

 or else the product, without exhibiting any marked excellence of 

 flavour, is endowed with good keeping qualities. Consequently 

 such races or varieties should be used in the manufacture of 

 butters for export. Whether there are races in which both these 

 advantages are combined cannot yet be definitely asserted. The 

 aroma produced by the bacteria cannot have originated in the 

 volatile acids of the butter, since it is also developed in cultures 

 free from fat, and containing no nitrogenous nutriment other than 

 peptone. Comparative experiments on the flavour of butters pre- 

 pared by the aid of different varieties of lactic acid bacteria were 

 made by ADAMETZ and WILCKENS (I.) in 1892. Owing to a note- 

 worthy discovery effected by H. W. CONN (I.) in 1895, the question 

 has latterly taken a new turn. He succeeded in isolating from a 



