RELATION BETWEEN THE BACTERIAL COUNT OF 
WHOLE MILK AND THAT OF THE CREAM AND SKIM 
MILK SEPARATED FROM IT 1 
By C. S. Leete 
Associate Market Milk Specialist, Bureau of Dairying, United States Department 
of Agriculture 
INTRODUCTION 
In studying the milk ordinances of many municipalities it is found 
that when a maximum bacterial count for milk is designated, a 
much higher maximum bacterial count for cream of the same grade 
is allowed. This increase covers a wide range, varying usually from 
300 to 500 per cent. A review of the literature upon this subject 
shotvs that but little work has been done, or at least few results have 
been published, dealing with the effect of separation upon the bacterial 
count of cream and skim milk. It would seem that the maximum 
bacterial standards for cream appearing in many milk ordinances 
are not based on scientific facts. 
The Bureau of Dairying of the United States Department of Agri¬ 
culture has been carrying on work with centrifugal and gravity 
separators in order to determine what effect separation has upon 
the bacterial count of the cream and skim milk. 
✓ 
CENTRIFUGAL SEPARATION 
A steam-turbine separator with a capacity of 1,350 pounds per 
hour was used. It was rim at its rated capacity. After use, the 
separator parts were cleaned with hot water containing a strong 
washing powder, then thoroughly rinsed with hot water, and steamed 
for three minutes over an open steam jet. After cooling, the parts 
were assembled, again steamed, and then placed in a clean inclosed 
cabinet until the next run. 
After the separator had attained its proper speed, mixed-herd 
milk at a temperature between 80° and 85° F. was separated. Sam¬ 
ples of the whole milk, cream, and skim milk were taken after separa¬ 
tion had been in progress about three minutes. The milk sample 
was taken at the outlet of the supply bowl, and the cream and skim 
milk samples from their respective spouts. The samples for bac¬ 
teriological analysis were immediately plated. Standard methods for 
bacteriological analysis of milk, as recommended by the American 
Public Health Association, 2 were followed. Plates were incubated 
for 48 hours at 37.5° C. Fat determinations were made with the 
Babcock fat test. Samples were taken from 100 separate runs of 
1 Received for publication Jan. 23, 1925; issued December, 1925. 
2 American Public Health Association and Association of Official Agricultural Chemists. 
STANDARD METHODS OF MILK ANALYSIS. BACTERIOLOGICAL AND CHEMICAL. Ed. 4, 40 p. f illUS. New 
York City. 1923. 
Journal of Agriculture Research, 
Washington, D. C. 
(695) 
Vol. XXXI, No. 7 
Oct. 1, 1925 
Key No. 1-1. 
