2 BULLETIN 1344, U. S. DEPARTMENT OF AGRICULTURE 
dealers, the cream volume on the bottled milk is of great commer- 
cial importance. 
It has been understood by many plant operators, and some investi- 
gators have shown, that pasteurization of milk decreases the cream 
volume to some extent. From the variation in the cream layer 
obtained by various dealers, it is apparent that the methods used in 
pasteurization as well as the effect of other operations in the han- 
dling of the milk, both before and after pasteurization, have an im- 
portant bearing on this problem. 
To obtain direct information, a questionnaire was sent to the plants 
in Minnesota that label their milk " pasteurized " under the approval 
of the State board of health. The questionnaire asked (1) whether 
a satisfactory cream layer was obtained on pasteurized milk, and (2) 
whether the depth of the cream layer was less than, equal to, or 
greater than that on raw milk of a similar butterfat content. Thirty- 
one replies were received, and the following are the answers to the 
first question : Yes, 23 ; not always, 1 ; at times, 1 ; no, 6. Following 
are the replies to the second question: Greater, 4: equal. 9: the same. 
1 ; less, 10; a trifle less, 4; do not know, 2. 
A similar questionnaire was sent by the Bureau of Dairying of the 
United States Department of Agriculture to the larger milk dealers 
throughout the country asking whether the cream layer of their 
product was injured by the pasteurization process. The following 
are the answers received: Cream volume uot injured, 128; cream 
volume only slightly injured, 31 ; cream volume injured, 21. Of the 
21 dealers who replied that the cream volume was injured, a few 
specified the percentage of reduction that they estimated had oc- 
curred. These estimated reductions varied from less than 10 per cent 
to 25 per cent. 
Replies received to both questionnaires indicated that the majority 
of the dealers are not experiencing any great difficulty with their 
present methods of 'pasteurization. 
Studies on the various factors which may or may not affect the 
creaming ability of market milk were undertaken by the division of 
sanitation of the Minnesota State Board of Health and the Bureau of 
Dairying in cooperation. 1 Experiments were carried on in the 
laboratory of the Minnesota State Board of Health; at the dairy 
hall of the division of dairy husbandry. University of Minnesota, 
the facilities of which were kindly turned over to the cooperators by 
the university: and at commercial milk plants. The laboratory 
tests included the effect of pasteurizing milk, of storage tempera- 
tures, of the rapidity of creaming, etc. The experiments at the dairy 
hall, University of Minnesota, included the effect of vat pasteuriza- 
tion of milk, using heating media of both high and low tempera- 
tures, the effect of cooling after pasteurization to various tempera- 
tures, the effect of storage temperatures, the e^eci of pumping milk 
with various t} 7 pes of pumps, etc. The experiments at the com- 
mercial plants included practically all of the factors previously 
mentioned, with especial regard to the results obtained with various 
types of pasteurizing apparatus, and to the effect of other processes 
that take place at commercial plants. 
1 Studies were begun by the division of sanitation during March, 1919, and cooperation 
with the Department of Agriculture, which had previously done sonie work on the prob- 
Jem. was started during April, 1923. 
