52 



Method of Experiment. 



It may be well first to explain the method of experiment which 

 has been found after considerable trial to be, all things considered, the 

 most satisfactory. 



When experiments in the creamery or elsewhere are desired, the 

 procedure is as follows : There is first placed in an ordinary flask a half 

 pint of milk, and this is sterilized by discontinuous steaming for three 

 or four successive days. This sterilized milk is inoculated with a small 

 amount of the Bacillus No. 4-1, and the culture thus made is allowed to 

 grow at about 23 ° 0. (74 ° F.) for a couple of day-. The object of 

 this growth is merely to increase the number of bacteria and thus make a 

 larger inocu^tion in tne creamery possible. After two days' growth 

 the culture is sent to the creamery and the rest of the experiment is 

 performed there by the butter-maker. 



A lot of cream, amounting to six or eight quarts, is placed in a 

 metal vessel and pasteurized, by being put into a tub of water into 

 which steam is allowed to run. The temperature of the cream is allow- 

 ed to rise to about 69 ° 0. (156 ° T.) and to remain there for some ten 

 minutes. The cream vessel is then removed and placed in cold water 

 and cooled as rapidly as possible. When the temperature has fallen to 

 about 23 ° G. (74 ° F.) the milk cultuie of the bacillus above described 

 is poured into it and is thoroughly mixed with it by stirring. The vessel 

 is then covered and placed in the ripening room of the creamery for 

 two days, at the end of which time the cream is churned and the butter- 

 milk re served for further use. The object of this ripening of a lot of 

 six quarts of cream is to increase the nurrber of bacteria in order that a 

 large and strong culture may be obtained for use in the large vat of 

 cream in the creamery. The buttermilk from the churning of the six 

 quarts of cream is then inoculated into the day's cream as soon as the 

 cream is placed in the vat for Ipening. The cream in the large vat 

 receives no preliminary treatment, the prepared milk being poured 

 into it directly. The cream is ^heu allowed to ripen at a normal tem- 

 perature for about twenty-four iaours and churned as usual. Before the 

 churning two or three gallons of the ripened cream is set aside to be 

 added to the next day's cream collection to insure a continuation of the 

 process. In this way tiie ripening is continued day after day, a small 

 amount of each day's churning being set aside for the next day's inocu- 

 lation, and the process is continued as long as the good effects ot the 

 original culture are seen. In the series of experiments which were in- 

 stituted it was found that the effect of the first culture could be kept up 

 in this way from three to six weeks, after which a new pure culture 

 from the bacteriological laboratory was needed. 



It will be noticed in these experiments that in practical use the 

 cream of each day's gathering is not pasteurized nor treated in any way 

 to insure removal of the bacteria which chanced to be in it. It may seem 

 strange that under these conditions the addition of a pure culture would 

 have decided effect upon the ripening of the cream. The explanation 

 of the matter seems, however, to be simple. As is well known,a proper- 

 ly ripened cream needs to be slightly acid in order to give the flavour 



