66 
Acidity in Milk. 
loped. As a matter of fact tlie progress of acidification in the 
cheese-vat before the whey is drawn off is very slow. Indeed, 
the degree of acidity shown by the whey at the stage when it is 
drawn off in the ordinary routine of the Cheddar process will be 
sometimes absolutely less than that of the milk before the rennet 
was added to it. This apparent parados is partly due to the 
fact that the observation of the change of colour produced by 
the addition of the Indicator is more easily perceived in a trans- 
parent fluid like whey than it is in an opaque one like milk ; 
and the eye therefore recognises the passage of the stage of 
neutralisation more readily in the former case than in the latter ; 
leading to the impression of a lower grade of acidity in the whey 
than was exhibited by the milk. 
The real rise of acidity in cheese-making does not take place 
until the curd is exposed to the action of the air, as in the 
process of cutting and piling. Then the free access of oxygen 
allows of the rapid development of lactic acid, and the acidity 
may in the course of an hour or less rise from five to twelve or 
fourteen degrees. 
The development of acidity in cream during the progress of 
ripening may be easily traced by the acidometer. Here the 
total acidity is materially augmented by the retention of carbonic 
acid in the viscous fluid, and may rise to as much as sixteen 
degrees before the cream becomes thoroughly clotted by curding. 
This viscosity of cream, which interferes somewhat with the 
delicacy of the acidometric test, may be counteracted by diluting 
the cream with a given amount of water, and multiplying the 
degree of acidity obtained in proportion to the volume of water 
which has been used. 
The acidometer is of gi*eat value in determining the stage to 
which a given sample of milk may have advanced in the process of 
spontaneous acidification. As the curding of milk is entirely 
due to the effect of the acid in neutralising the alkaline phos- 
phates by which the casein of the milk is retained in its viscous 
condition, it is easy to satisfy oneself by the aid of the appliance 
how far any given sample of milk has progressed in this direc- 
tion. 
In fact, no one who handles milk, for whatever purpose, can 
do so with any certainty of what he is about unless he can 
estimate its acidity, and this it is now possible to do with as much' 
ease and certainty as its temperature can be gauged by the 
thermometer or its weight determined by the balance. 
Francis T. Bond. 
