286 
The WorTi oj Acidity in Gheese-mal-inrj. 
the commencement of decomposition in the evolution of gas. 
This gas, unlike that developed by the'natural fermentation of the 
sugar of the milk (carbonic acid gas), is insoluble in the watery 
constituent of the milk, and therefore makes itself evident as 
bubbles. A certain quantity may escape to the surface of the milk 
during the stage of curding, but the bulk will remain imprisoned 
in the curd, and may even so affect its specific gravity that instead 
of sinking in the whey when free to move in it, as sound curd 
should do, it will rise to the surface of the whey, forming the 
" floating curd " with which so many indifferent cheese-makers are 
familiar, and which has been the bete noire of so many cheese- 
factories, especially in America. Professor Sheldon suggests that 
it was in consequence of the trouble experienced in the earlier 
American cheese-factories from this cause that the attention of 
American dairymen was directed to the value of acidity in cor- 
recting it. This was very probably the case, for it is not only in 
America but in this country also that the effect of artificially de- 
veloping acidity in milk which is suspected to be unsound has 
been empirically discovered to be a corrective, and various agents 
have been employed for the purpose of creating it. In some cases 
the result is brought about by the addition to the milk, before 
it is renneted, of a certain amount of sour whey, the action of 
which is to inoculate it with a special dose of the ferment by 
which aciditj^ is developed. In others the addition of an acid, 
such as lactic acid (the natural acid of the milk), or an acid salt, 
such as the acid phosphate of lime or alum, has been employed 
with equally useful effect and without the risk, attendant on the 
employment of sour whey, of introducing with the acid-producing 
germs others which may exist iu the whey with them, and 
which would give rise to special sources of mischief during the 
ripening stage. 
But probably the least objectionable method of neutralising 
the defect in question is to keep the milk in the vat at tlie 
renneting temperature sufficiently long to raise the acidity to 
the required point befoi'e renneting it, taking care, of course, 
that it is well stirred meanwhile, so as to prevent the cream 
rising. The next best remedy is to push on the acidification of 
the curd during the draining stage, by cutting it up well and 
piling it often, so as to expose it freely to the air, at the same time 
l-eepinri it ivarm. In either of these ways the mischievous effect 
of deficient acidity in the milk may be more or less perfectly 
remedied, for the development of acidity airests the multiplication 
of the special germs which flourish in neutral or alkaline luilk, 
and the growth of wliich is attended not only by the evolution 
of the gases of putrefaction, as above indicated, but ])y modifi- 
