436 BUTTEK, CHEESE, ETC. 



cream be used. An acidity of about 60 will generally yield 

 good results. 



In order to ensure that a good flavoured butter is produced, 

 it is necessary that the proper organisms be present ; this is 

 best ensured by pasteurising the cream, and after cooling adding 

 a starter, which has been found to produce a good flavour. The 

 starter provides an enormous excess of lactic acid bacteria, which 

 at the ripening temperature develop rapidly and overgrow any 

 other organisms that may have found entrance. 



A starter is prepared by sterilising 1 to 2 litres of milk, adding 

 a tube of one of the preparations on the market, which are pure 

 cultures of lactic acid bacteria, and keeping the milk at about 

 70 F. till thick. 



A rough, but usually very successful, method is to allow a 

 specimen of milk, which develops a clean acid taste on keeping, 

 to stand at about 70 F. till sour. The lactic acid organisms 

 are very active at this temperature, and, as they tend to over- 

 grow any others that may be present, a fairly pure culture is 

 the result. 



Starters may be kept going by adding to 1 to 2 litres of milk 

 that has been sterilised a little of a previous starter, and keeping 

 at 70 F. 



Buttermilk Definition. The term buttermilk is applied 

 to the aqueous portion left after churning. It differs only 

 slightly in composition from skim milk. As the cream used 

 for churning is usually slightly sour, the buttermilk contains 

 appreciable amounts of lactic acid ; it will also contain water or 

 any other substance which has been added during churning. 

 There is, in suspension, a considerable amount of Storch's mucoid 

 protein, which may be removed by passing it through a cream 

 separator, when it is deposited on the sides of the drum. 



Cheese. 



Cheese is prepared by the action of rennet on milk ; this separ- 

 ates it into whey and curd ; the curd is finely divided, pressed 

 to separate the whey and to consolidate it, and, usually, salted. 

 From this, cheese is produced by ripening, which is due partly 

 to the action of micro-organisms and fungi, partly (as Babcock 

 and Russell have shown) to the action of an enzyme natural to 

 milk. 



Action of Rennet. The action of rennet is to split up the 

 casein into a dyscaseose, the calcium compound of which is 

 insoluble and which forms curd, and a soluble caseose ; the 

 insolutle curd carries down with it a large proportion of the fat. 



Rennet. This substance is an enzyme produced in the stomachs 

 of mammals ; it occurs in the human stomach, and the curdling 



