298 DAIRYING. 



process of sour-cream butter-making is therefore, at the bottom, 

 a question of keeping the fermentations during the ripening of 

 the cream in the right track, of controUing the same so as to 

 exclude all but lactic-acid-producing bacteria. The old 

 original way of reaching this end was to allow the cream 

 to sour spontaneously, trusting to luck to obtain the desired 

 fermentation of the cream by leaving it standing in a warm 

 room for a couple of days. Later on, a buttermilk starter 

 from a preceding churning or a skim-milk starter was added 

 for the purpose of ripening the cream ; by this means 

 the lactic-acid bacteria contained in the starter were intro- 

 duced in such large numbers that they generally were able to 

 crowd out other kinds of bacteria that might be found in the 

 cream, and which, if left alone, would produce undesirable 

 fermentations in the cream and bad flavor in the butter. 

 The next step in advance was the introduction of pure 

 cultures of lactic-acid bacteria; these consist of one or a 

 few forms of bacteria, and when introduced in milk or 

 cream will be apt to overpower all other forms of bacteria 

 therein, and thus produce the pure mild flavor of sour- 

 cream butter desired. 



The honor of having first introduced pure cultures in 

 butter-making belongs to Dr. V. Storch, the chemist of 

 the Danish state experiment station in Copenhagen; the 

 bulletin describing Dr. Storch's investigations of this 

 subject, "On the Ripening of Cream," was published in 

 1890. Other bacteriologists in Europe and in this country 

 have worked along this same line, and as a result we find 

 that pure cultures are at the present time used almost 

 universally in the manufacture of sour-cream butter in 

 the creameries and dairies of northern Europe, and also 

 in this country their use has become general and is spread- 

 ing. The expected result of adding a pure culture-starter, 

 viz., that of excluding all undesirable fermentations in 

 the ripening of the cream, will not, however, follow with 

 any certainty unless the seeding with the pure culture 

 is preceded by pasteurization or sterilization of the cream, 

 that is, at least a partial destruction of the bacteria already 

 found therein. In Europe, notably in Denmark and the 



