APPLICATIONS OF LACTIC ACID FERMENTATION 117 



the tops of the cans project. The cans are covered with steam 

 sterilised double covers which allow of air circulation. As nothing 

 is gained by keeping the starter cold overnight, there is no reason 

 to add more culture than is necessary to ripen the starter before 

 the following morning ; about \ to 1 per cent, is sufficient. Im- 

 mediately before use the starter is skimmed, as the top layer will 

 be richest in foreign germs if infection has taken place 1 . The 

 starter is given a more liquid consistency by stirring it vigorously, 

 after which it is poured into the cream ripening tank . As the starter 

 is more easily titrated than cream, its acidity should be checked 

 from time to time. Experience has shown that the best results 

 are obtained with an acidity of 90 to 100 (number of cubic 

 centimetres of normal soda per litre, corresponding to 18 to20c.c. 

 of decinormal soda per 20 c.c. of milk). This corresponds to 

 36 to 40 Soxhlet-Henkel degrees. If the starter becomes weak 

 and shows a lower acidity although it has been kept at a tempera- 

 ture over 22 C. all the time, the culture used is weak, while if the 

 acidity is too high the milk has probably been oversoured, and the 

 most beneficial bacteria will not be in full vigour. The culture will 

 thus often contain rod-shaped lactic acid bacteria, in which case 

 it will be best to use a new culture. 



What has been said regarding the starter also applies to the 

 culture from which the starter is made, only in this case still 

 greater care is necessary, for an infection in the starter need only 

 degrade the quality of a single churning, while an infected culture 

 may cause repeated trouble. Fortunately it is easier to keep the 

 culture pure, and there is not the same difficulty in obtaining the 

 small amounts of finest grade milk required for this purpose as 

 may be experienced in obtaining sufficient quantities of milk in 

 the condition in which it should be used for the starter. Herein 

 lies the advantage of propagating the culture and the starter 

 separately instead of simply inoculating the new starter milk 

 with some of the old starter. It is a good plan to keep two or 

 three cultures going independently of one another, inoculating 

 daily into fresh milk, for by comparing the tastes of the different 

 cultures the detection of defects in taste is much facilitated and 

 as it would be a very exceptional misfortune if all the cultures 

 became bad at once, at least one good culture will always be 

 available if the precaution is taken of renewing any bad cultures 

 as soon as possible. Several forms, of culture making apparatus 

 are on the market ; it is important that means should be provided 



1 If the milk is stirred during the souring there is no benefit to be derived 

 from this precaution. According to Bostrorns experiments at Alnarp 

 dairy, the lactic acid bacteria thrive better if the milk is stirred occasion- 

 ally. By this means local over- or under-souring is avoided. 



