292 IOWA DEPARTMENT OF AGRICULTURE. 



ized it becomes slimy and lumpy. This was a difficulty commonly encoun- 

 tered when sour hand separator cream was first being pasteurized. This is 

 due to the fact that this quality of cream was pasteurized in the same way as 

 was formerly practiced in the pasteurization of sweet cream and milk. In 

 order to obtain good results by pasteurizing hand separator cream it is 

 essential that special precaution should be taken. 



The first point to be considered in order to avoid sliminess and lumpiness 

 in connection with pasteurization of hand separator cream, is to expose a 

 comparatively small amount of cream to the heat at one time. The cold 

 cream running in should not be allowed to mix with a comparatively large 

 amount of the heated cream already in the pasteurizer. If the cold cream is 

 allowed to mix with that already heated to a large extent in the bottom of 

 the pasteurizer, the whole will be heated very gradually. Such a condition 

 is likely to cause the sliminess referred to above. The heat should be 

 applied to as thin a layer of cream as is consistent with the use of the par- 

 ticular pasteurizer. It seems that when sour cream is heated quickly to 

 pasteurization temperature, the curd breaks up into small or fine particles, 

 while if heated gradually, in many instances, the curd seems to coagulate 

 into a smooth and slimy condition. 



It has also been demonstrated that the slimy and lumpy condition is 

 most likely to form when the cream has an acidity of about three per cent 

 to four per cent. At about this degree of acidity the cream will coagulate 

 when heated, and is likely to coagulate in an abnormal way. If the acidity 

 is much lower than this the cream does not coagulate on heating. If the 

 acidity is higher than four per cent, the coagulation has already taken place 

 in a normal way, and if such cream is rapidly heated, the coagulation will 

 be broken up into smaller particles without any abnormal efifect upon the 

 cream. 



The richness of cream is also a very important point in order to prevent 

 sliminess. The greater the per centage of fat, the less serum there is. As 

 it is the serum portion that causes the difficulty, the less serum or substances 

 not fat in cream, the better it is for pasteurization. Rich cream becomes 

 more liquid on heating, due to the melting of the fat. Cream containing a 

 small amount of fat is likely to become thicker by pasteurizing it, due ta 

 the coagulation of the relatively large amount of serum as described 

 previously. 



In order to be able to heat the hand separator cream to a comparatively 

 high temperature, it should not be allowed to move sluggishly over the 

 heating surface. By this I do not mean that the time it takes for the cream 

 to pass from the inlet to the outlet of the pasteurizer should be of very short 

 duration, but I mean that the cream should not be exposed very long at one 

 place to the heating surface. If cream moves rapidly on a smooth heat- 

 ing surface, burning is in a large measure prevented. By increasing the 

 speed of the agitator a trifle the cream in most types of pasteurizing ma- 

 chines would be caused to move more rapidly over the heating surface. An 

 increase of speed would also, in a measure, prevent the cream from gather- 

 ing at the bottom of the pasteurizer. 



The temperature at which to heat in order to obtain good results in the 

 pasteurization of hand separator cream may vary. A temperature of about 

 180 degrees F. has proven to give good results. At this high temperature 



