38 



2. First care of milk at the factory . — While the milk is accumulating 

 in the vat, it should bo stirred frequently up to time of setting in order 

 to keep the cream from sej)a rating. When the vat is full enough, the 

 amount of milk present being figured, the acidity of the milk is deter- 

 mined or a rennet test made. If, r.s usually happens, the milk is sweet, 

 heat to 84° to 86° F. and ripen (reference No. 8, p. 49). 



3. Ripening milk. — (References No. 3, p. 68, and No. 8, p. 49.) 

 This consists in the formation of a certain amount of lactic acid. Its 

 object is to control more completely the operations of cheese making. 

 Lactic acid may be formed by allowing milk to stand a while at a tem- 

 perature of 84° to 86° F. Wlien lactic-acid bacteria are not present 

 abundantly or are kept back in growth by injurious organisms, it is 

 necessary to use a "starter." 



4. Prejmration of starter. — (References No. 3, p. 43, and No. 8, p. 

 50.) A starter is a material containing large numbers of lactic-acid 

 organisms added to milk or cream for the purpose of causing lactic fer- 

 mentation. Starters are of two kinds — (1) natural and (2) pure 

 culture (references No. 8, p. 51, and No. 9, pp. 1*97, 199.) A nat- 

 ural starter may be prepared as follows: Milk of the best possible 

 character, taken under precautions necessary to insure cleanliness, is 

 heated to 90° F. and then kept at 65° to 70° F. In twenty-four hours 

 this is ready for use. Some of this starter may be used in preparing a 

 starter for the following day, putting a little into some skim milk that 

 has been heated to 180° F. for thirty minutes and then cooled to 70° 

 F. and allowed to stand twenty-four hours. The starter may thus be 

 propagated from day to day. A new starter should be prepared as 

 soon as any unfavorable quality is noticed. Pure-culture starters are 

 special preparations consisting of certain selected organisms known to 

 be adapted to forming lactic acid. Several such are on the market 

 and give good results (reference No. 8, p. 51). Starters should not 

 be prepared from the milk mixed in the vat or from whey (reference 

 No. 8, p. 48). 



5. Use of starter in cheese making. — In using a starter reject the 

 upper portion and pass the rest into the milk through a fine strainer. 

 The amount to be used depends upon the acidity or ripeness of the 

 milk at the start, but will vary from 2 to 5 pounds for each 100 pounds 

 of milk (reference No. 3, p. 69). Experience must serve as a guide 

 to some extent. 



6. How to ascertain the proper degree of ripeness. — Since ripeness in 

 milk is the same as acidity, the ripeness can be measured (1) by deter- 

 mining the acidity, as described in I^ecture 5, paragraph 19, or (2) by 

 making a rennet test. The general aim is to have such an amount of 

 acid formed when the rennet is added that the curd will remain in the 

 whey not more than two and three-(iuarters to three hours. This 

 result is usually accomplished when the acid test shows 0.19 to 0.21 



