CHEESE MAKIJTO. 357 



the principles of his business, and then work out his own 

 practice after many mistakes and defeats. 



The Chemistry of Cheese Makii^g is a very involved 

 and intricate study, but it is not difficult to reduce it to 

 a system and explain the causes for the curious effects of 

 the process. When milk is left exposed to the atmos- 

 phere for a varying length of time it becomes acid, and 

 separates into two parts, one a solid and the other a 

 liquid. The time required for this change varies with 

 the temperature, being longer or shorter as the tempera- 

 ture may be lower or higher. The production of acidity 

 is due to the formation of lactic acid by the decomposi- 

 tion of the sugar of the milk. The acid thus formed 

 combines with the free soda which always exists in 

 normal milk in its fresh state, and this combination goes 

 on until the alkali is all exhausted, when acid begins to 

 accumulate. 



The caseine of the milk is soluble in an alkaline flu'id, 

 but not in a neutral one. Consequently, when the alkali 

 (the free soda) in the milk is neutralized by the formation 

 of lactic acid, the caseine is precipitated or becomes 

 solid, being no longer soluble in the milk. But the 

 curd does not separate from the whey until heat is applied, 

 when the curd contracts in bulk and forces the whey out 

 from among its particles, all the more freely when it is 

 cut into small pieces and is raised to a considerably high 

 temperature, as that used in cheese-making; viz., eighty 

 to one hundred degrees. In making cheese it is not 

 usual to permit the milk to' become sour and precipitate 

 the curd in that way. This process is performed by the 

 addition of some substance which acts chemically upon 

 the milk to hasten the production of the curd with de- 

 veloping acidity. Any acid will curdle milk, and in the 

 manufacture of some kinds of cheese, vinegar, tartaric 

 acid, lemon juice, cream of tartar, hydrochloric (muri- 

 atic) acid, and even oxalate of potash (salt of sorrel) have 



