APPLICATIONS OF LACTIC ACID FERMENTATION 111 



manufacture involves a very thorough washing. The explanation 

 is that butter-fat is able to absorb essential oils and other odiferous 

 substances, both pleasant (a property which has been made use of 

 in perfumery) and unpleasant, and the aroma of the cream will 

 therefore pass into the fat globules. The greater the proportion 

 of fat globules present, the less aroma will be available for each 

 globule, and experience also shows that a high fat percentage is 

 not conducive to the production of an aromatic butter. Un- 

 fortunately there is a tendency to work with richer cream in 

 dairies where increasing quantities of milk have to be treated ; 

 thus in Denmark it was formerly considered inadvisable to churn 

 cream containing more than 20 per cent, of fat, but of late the 

 practice has generally been to increase the percentage to thirty or 

 even more. Fortunately difficulties in churning prevent the raising 

 of the latter limit to any extent. 



As far as the pasteurising of the cream is concerned, it need only 

 be mentioned that out of consideration for the keeping properties 

 of the butter, the pasteurising temperature should be as high as 

 possible. As the cooked flavour which milk acquires on heating 

 does not originate in the fat, cream is not particularly sensitive to 

 this treatment, and if the subsequent cooling be sufficiently rapid, 

 no harm will be done by raising the temperature to 95 C. In 

 this connection we must bear in mind the well-known fact that 

 milk fat occurs naturally in different stages of supercooling, and 

 that a partial alteration of this condition must take place before 

 the butter can " come." As all the constituents of the fat melt 

 completely on pasteurisation, freshly pasteurised cream is difficult 

 to churn. The longer the cream has stood, the nearer will the fat 

 globules be to the point of crystallisation, and the quicker will the 

 butter come. In order to promote crystallisation, it is usual to 

 cool the cream as completely as possible for a short time im- 

 mediately after pasteurisation, and then to warm it up to the 

 souring temperature 1 . The crystallisation of fat, however, takes 

 time, and less is achieved by a cooling of short duration at a low 

 temperature than by a more prolonged cooling at a somewhat 

 higher temperature. Prolonged cooling, lasting many hours, is 

 more practicable after the souring process than before, and under 

 these circumstances the cream is only cooled to the souring 



1 Cf. the author's theory of churning (" Maelkeritidende," 1907, p. 943) 

 van Dam's investigations (" Molkereizeitung," 1915, Nos. 25 and 26) clearly 

 show the great importance of cooling the cream to a low temperature. At 

 16 C. all the fat was liquid even after twenty-one hours. At 11 C. one- 

 half of the fat had solidified in the same time, and at 6 to 8 com- 

 plete crystallisation had taken place in four hours. It is, therefore, 

 recommended to cool the cream for some time to 6 C., especially in 

 autumn. 



