170 Report or rHeE CHEMIST OF THE 
the quantity of acid in the milk, not only before adding rennet, 
but continuously throughout the rest of the process of manufac- 
ture. is 
The amount of acid in cheese-curd is roughly measured in a 
mechanical way by means of the so-called “ hot-iron test.” When 
a piece of curd is pressed against a hot iron and then drawn 
away carefully, fine, silky threads are formed, adhering to the 
iron. This phenomenon is closely associated with the formation 
of acid and the length of the strings shown by the hot-iron test 
is utilized as a measure of the amount of acid present and as an 
indication when to perform certain operations. Thus, when 
the curd strings on the hot iron to the length of one-eighth of 
an inch, the whey is removed from the curd, after which the curd 
is “packed” in a pile and allowed to lie until it has passed 
through the so-called “ matting” or “ breaking-down” process, 
when it furnishes strings an inch or more in length by the hot- 
iron test. When this stage is reached, the remaining steps of 
the manufacturing process are at once completed, such as mill- 
ing, salting, and putting in molds for pressing. 
While it has been generally supposed that the presence of some 
acid, presumably lactic acid, in the cheese-making process is, in 
Some way or other, responsible for the most important changes 
taking place, such as the shrinking of the curd, the acquired abil- 
ity to form strings on hot iron and the change in appearance and 
plasticity of curd, no one has ever been able to show in what 
way these changes were brought about by acids. It has been 
commonly supposed that the observed changes were purely physi- 
cal in character and were not the result of chemical changes in 
the curd. In the following pages it is our purpose to consider 
more fully than has been done previously the real function of 
acids in relation to the important changes taking place in cheese- 
curd during the cheddar process of cheese-making. 
Since Sjéquist’s® investigation, we have learned that proteids 
can build salts with acids and bases, and this subject has been 
considerably developed in the last few years. Bugarszky and Lie- 
bermann? have shown that egg-albumin forms with hydrochloric 
acid a salt analogous to ammonium chloride, which they call 
3Skandin, Arch. f. Physiol., 5: 277 (1894). 
4Pfluger’s Archiv, 72: 51 (1898). 
