334 SCIENCE AND PRACTICE OF CHEESE-MAKING 



Neutral salts and acid salts. — As already stated, 

 there rarely appears to be any free acid in normal 

 cheese. The calcium compounds (mainly phos- 

 phates and citrates) are sufficient in amount to 

 make use of the lactic acid which is formed, as 

 previously explained (p. 149). The same process 

 continues in the unripe cheese which previously 

 begins in the milk and curd in the cheese-vat. It 

 is probable that in ripened cheese the ammonia com- 

 bines with the acid salts to neutralize their acidity 

 more or less completely, because, in overripe cheese, 

 we usually find the reaction alkaline instead of 

 acid. 



Salt. — So far as known, salt undergoes no chemical 

 change in cheese-ripening. As the water decreases, 

 the brine or whey of the cheese simply becomes 

 stronger, as a matter of course. 



Gases. — In ripened cheese, different gases in dif- 

 ferent relative proportions have been found, but 

 little work has been done in connection with ched- 

 dar cheese. The amounts and kinds of gases un- 

 doubtedly vary according to various conditions, 

 depending primarily ( i ) upon the kinds of micro- 

 organisms introduced into the cheese through the 

 milk, and (2) upon the temperature at which 

 the cheese is ripened. The gases usually found in 

 largest amounts are carbon dioxld and hydrogen. 

 We have found also hydrogen sulphid. The dry 

 matter in cheese is slightly reduced, owing to the 

 formation and escape of gases. In one experiment 

 at the New York experiment station having for its 

 object a determination of the rate and amount of 

 carbon dioxld formed during ripening at 60° F. by 



