BULLETIN 141 APRIL, 1905 



ONTARIO AliRll^yLTORAL mm AND EXPERIMENTAL FARM 



GAS-PRODUCING BACTERIA AND THEIR EFFECT ON MILK 



AND ITS PRODUCTS. 



By F. C. Harrison, Professor of Bacteriology. 



One of the commonest troubles in a cheese factory is the affection 

 known to cheescmakers as "gassy" milk, which gives rise to off-flavors, 

 and swelling and huffing of the cheese, and whilst it is impossible to give 

 figures showing the financial loss by depreciation in the value of such 

 tainted cheese, we know that such losses are frequently very serious. 



Considering the importance of the bacteria which induce these 

 changes in milk, very little attention has been given them by American 

 bacteriologists, but in Europe, a number of valuable investigations have 

 been made but under conditions which are very different from our own. 

 On this account, a number of experiments were planned and carried out 

 in the Bacteriological Laboratory of the College, aided by the facilities 

 afforded by the College cheese factory. 



Many of the details of these experiments are of a technical nature, 

 dealing with the peculiarities of the shape, structure, and growth of the 

 sixty-six varieties of gas-producing bacteria isolated from various sources. 

 No mention will be made of these in this bulletin, but, in addition to the 

 scientific data, a number of practical points were investigated which are 

 now set forth in this bulletin. 



The gas-producing bacteria were isolated from the milk supplied to 

 the College Diary by farmers in the vicinity. This milk compared favor- 

 ably with the ordinary factory supply, as constant endeavors have been 

 made to instruct the patrons in the most approved manner of handling 

 their milk. In spite of this fact, the College cheesemaker is very often 

 bothered with gassy fermentations in the curd and cheese, and this inves- 

 tigation was undertaken in order to find out the habitat, ascertain the 

 number and study the effects of the various species of gas-producing bac- 

 teria present in milk and cheese. 



Samples of milk were taken in sterile tubes from the mixed milk of 

 each farmer, and immediately brought to the laboratory and analysed. 

 This sample, after taking out the quantity that was used for the analysis, 

 was kept for a day or two at blood temperature in order to ascertain if 

 gas was produced. Occasionally, we found gas bubbles in the milk sam- 

 ple, but no gas-producing bacteria developed in the gelatine plates, a pro- 

 bable proof of the small number of this class of organisms in the sample 

 at the time the examination was made. 



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