BITTER MILK AND BITTER CHEESE 251 



regarded from a bacteriological standpoint seems almost self-evident, viz., 

 the difficulty experienced in the working up of milk at such times of the year 

 as a change is made from dry to green fodder, and vice versd. The bacterial 

 flora of fresh grass is of a much more diversified character than that on dry 

 hay ; only a few species remaining alive and capable of development in the 

 latter. 



183. Counteracting 1 Puffiness in Cheese. 



The reader will now probably inquire whether any method exists whereby 

 milk that will produce puffy cheese may be recognised as dangerous before it 

 is worked up and rejected by the cheese-maker. This course will be advisable 

 when the gas-forming bacteria greatly preponderate, a condition ascertainable 

 by the so-called fermentation test. A sample of the milk to be examined is 

 kept in a fermentation flask ( 126) for twelve hours at 40 0., a conclusion 

 based on experience being then formed as to its suitability or the reverse, 

 according to the changes occurring during this period. Fuller particulars on 

 this point will be found in Adametz's monograph, as also in the highly com- 

 mendable text-book of W. FLEISCHMANN (I.). 



As a means of preventing the malady, FREUDENREICH (IX.) recommends the 

 addition of 3 per cent, of common salt to the freshly precipitated curd, freed 

 from the main bulk of the whey. For restricting incipient puffiness, Adametz 

 counsels setting the cheese to cool, since the ferment is found, by experience, to 

 be violent and injurious solely at higher temperatures. 



From the results of an investigation made by H. L. BOLLEY and C. M. 

 HALL (I.) it must be concluded that gas-forming bacteria are not present in milk 

 at the moment it leaves the udder. If this observation is confirmed by renewed 

 (highly, desirable) researches in other places and under different conditions, and 

 thus become a general law, it will indicate the means of preventing puffiness, viz., 

 by taking care to keep the fresh-drawn milk free from dirt and dung, which are 

 the vehicles by which the gas-forming bacteria are introduced. 



184. Bitter Milk and Bitter Cheese. 



According to a rule based on experience, and observed by all housewives 

 skilled in cookery, boiled milk must be stored in uncovered vessels, otherwise 

 it is liable to turn bitter. The attention of Pasteur was also directed to this 

 matter in the course of his studies on spontaneous generation. We have already 

 seen, in a previous section, that the French investigator here made the important 

 discovery that, though the lactic acid bacteria are thus destroyed, the more highly 

 resistant spores of butyric acid bacteria can withstand such a brief exposure to 

 boiling heat. Now, since the majority of these latter are anaerobic, they can 

 then only manifest their activity provided the admission of oxygen is either 

 entirely prevented, or at least restricted, a condition ensured by covering the 

 milk-pan with a lid. There then gradually accumulates within the pan an 

 atmosphere of carbon dioxide, &c., produced by the vital activity of bacteria and 

 preventing the access of oxygen to the strongly fermenting milk. The existence 

 of this gaseous stratum can be detected by the sense of smell on carefully raising 

 the lid. 



The bitter flavour developed in the milk was formerly ascribed e.g. by 

 K. KRUEGER (II.) to the chief product formed by these bacteria, viz., butyric 

 acid, until WEIGMANN (IX.) in 1890 showed that no bitter taste is produced in 

 milk by the addition of butyric acid. Like HUEPPE (VII.), he attributes the 

 bitter flavour to the peptone formed from the albuminoids in milk. Later re- 

 searches on this point have led, in the main, to the same results. Consequently 



