BUTTER-MAKING 243 



culture that has just been inoculated in milk, at higher temper- 

 atures, because otherwise the ripening would be too slow. 



" When the starter has been built up to the desired quantity 

 it is carried on, or propagated, from day to day. When a ripe 

 starter is to be added to the cream or used for inoculation, it is 

 best to skim off the top to a depth of about one inch. The top 

 always has a poorer flavor due perhaps to the contamination 

 from the air and the influence of the air itself especially on the 

 growth of fungi like Oidium lactis. These skimmings can be 

 added to the cream and need not be wasted, but their removal 

 before taking some of the starter for an inoculation helps to 

 maintain its good qualities. In this manner the poorer por- 

 tion is not used for propagation, on the same principle that poor 

 seed corn is discarded. The pasteurized milk is inoculated with 

 such a quantity of the mature starter as will ripen the milk by 

 the time it is to be used, usually twenty-four hours. An inocu- 

 lation of two per cent generally accomplishes this. The length 

 of ripening can also be controlled by the temperature. But 

 ripening at a very high or very low temperature is likely to pro- 

 duce bad flavors. If it is desired to retard the ripening, it is 

 better to lower the temperature a little rather than to reduce 

 the inoculation too much. Reducing the inoculation favors the 

 competing bacteria. 



"The quality of a starter should always be examined before 

 it is used for inoculating or before it is added to the cream. 

 At any time it is likely to get so bad that it may do more harm 

 than good, and then it is not worth carrying on. In such a case 

 the maker has to resort to a new culture or a new starter. For 

 this emergency it is well to save out a quart or so of a good 

 starter and keep it cold. A good starter kept at a low tempera- 

 ture will retain its good quality for a week or so. This reserve 

 starter can be built up much more quickly than a commercial 

 culture. 



" A starter sometimes gets so bad in a few days that it is not 



