ILLINOIS DAIRYMEN'S ASSOCIATION. 239 



terial in which they are growing. It may be a useful or a harm- 

 ful one for the dairyman. 



The character of the change will be largely determined by 

 the kind of bacteria present, whether from the dust of the air, 

 dusty hay, the flanks of the animal, the seams of imperfectly 

 washed utensils, from a good home made starter or a commercial 

 starter from a pure culture. The change may be retarded by ex- 

 cluding bacteria, by stopping their growth with cold, or by kill- 

 ing with heat. The change may be hastened by introducing 

 bacteria, or by a favorable temperature. The rapidity of the 

 change will depend on numbers of bacteria present and whether 

 the temperature is favorable to their rapid growth or not. In the 

 farm dairy the ripening of the cream is usually brought about by 

 the bacteria which accidentally gain access to the milk and cream 

 and fortunately for the dairyman the lactic acid germs usually 

 predominate, especially in the clean, well kept dairy. 



An understanding of these principles should materially as- 

 sist in the handling of dairy products to bring about desired or 

 prevent undesirable changes. 



The cream should be kept cold, below 50 degrees if possible, 

 until enough is secured for a churning. It should then be warm- 

 ed up to from 65 to 70 degrees and held until it becomes sour and 

 has a pleasant acid taste; occasionally a little higher temperature 

 may be needed. If the cream was sweet it will usually require 

 18 to 24 hours to sour it. No cream should be added to that to 

 be churned for at least 12 to 18 hours previous to churning; dur- 

 ing this period it should be stirred several times to insure uni- 

 form ripeness. When cream of unequal degrees of ripeness is 

 churned, it requires a longer time to churn and there is a much 

 larger loss of butter fat in the butter milk. When a layer of 

 cream is seen on the butter milk that has stood, it is usually due 

 to churning too sweet, or part sweet and part ripe cream. 



At least two hours before the cream is churned it should be 

 cooled to 50 — 56 degrees. If not too ripe it may be held at this 

 low temperature for 12 hours. This cooling will do much to 



