266 LIME AND MILK. 



The addition of soluble lime salts (though the salts themselves 

 may be neutral) radically changes the balance between casein, 

 acid and salts. The adding of the lactate, citrate or phosphate 

 of lime will increase the acidity of the whey. 



Lloyd found in 1892 that during cheesemaking a large quantity 

 of lime is subtracted from the curds. The curd in the cheesevat 

 is a casein salt of lime. Attention has been drawn before to the 

 double potentiality of the casein molecule and we must assume 

 that in contact with lime the anhydric principle is liberated. 



Some authors hold that the lime in the curd is not chemically 

 bound but retained there by adhesion. But this theory is unable 

 to explain the subsequent processes in the curds. 



Duclaux states that curd contains more than two-thirds and 

 sometimes the whole of the phosphates of lime in the milk. Not 

 only the suspended salt but part of the dissolved salt is engulfed 

 by the coagulum. The latter, however, with more difficulty and 

 in proportionate smaller quantities as the milk at the moment of 

 curdling showed a higher acidity. 



This does not explain why neutral lime salts added to the milk 

 before renneting will increase the acidity of the whey. I am 

 inclined to believe that in curdling, acid salts as well are enclosed 

 by the coagulum and that this partly explains the lower acidity 

 of the whey. Apparently neutral lime salts have the tendency 

 of taking the place of acid salts in the forming of coagulum. The 

 casein can only retain a proportionate quantity of salt, the displaced 

 acid salts remain in the whey and increase the acidity. 



The curd formed in the cheesevat is a casein salt of phosphate of 

 lime and the whole process of maturing cheese hinges on the gradual 

 elimination of the lime from the curd by lactic acid and the subse- 

 quent effect of lactic acid on casein. 



Professor Lloyd described ripening Cheddar cheese as "a solid 

 acid in an acid pickle," and this seems a very apt description. 

 Professor Freudenreich maintained that the ripening of Gruyere 

 cheese is caused by the symbiose (co-operation) of four species of 

 lactic acid bacteria. Probably both authors are right, the four 

 species of bacteria produce the lactic acid which disintegrates the 

 casein. 



Fresh curds show an entirely different consistency from ripe 

 cheese. The curd is whitish, practically tasteless, hard and tough. 

 After the lapse of a longer or shorter time the curd changes. The 

 colour is different, the curd becomes smooth, soft and silky. This 

 difference is due to a chemical change in the casein. The lactic 

 acid in the cheese has combined with lime derived from the casein, 

 forming lactate of lime. Even after this the lime present continues 

 to influence the ripening process, as the lactate of lime forms the 

 nutritive medium for certain species of germs. A deficiency of 

 lime in the milk, therefore, materially influences the qualit}^ of the 

 cheese made out of such milk. The lactic acid forming in the milk 

 rapidly absorbs the available basic lime salts and begins to act on 

 the casein much earlier than in the ordinary milk. . » > . 



The coagulum formed on renneting is dift'erent in composition. 

 Casein coagulates with rennet, but precipitates Mdth acid, there- 



