Pasteurization of Milk 



25 



per cent solution of sodium chloride 

 may be advantageously employed as a 

 wash water, with the collection of as 

 much of it as is possible after it has 

 flowed or been washed over the milk 

 contact surfaces. Sterile spoons of the 

 tea or dessert spoon size are very use- 

 ful in the collection of samples of such 

 waters when the latter are small in 

 amount and are in otherwise inacces- 

 sible portions of the apparatus. They 

 make it possible to remove by physical 

 force with the wash or condensation 

 water perceptible portions of the 

 greasy films on the metal surfaces) 

 which almost invariably harbor exces- 

 sive numbers of bacteria. 



The tests should be performed by the 

 Standard Methods of Bacteriological 

 Water Analyses of the Laboratory Sec- 

 tion of the A. P. H. A. 



Tests for Defects in Design or Oper- 

 ation of Apparatus. In addition to the 

 collection of the samples for the deter- 

 minations of the sterility of the appara- 

 tus, samples of milk, foams, drips, etc., 

 should be collected from each unit of 

 apparatus to check up the possibilities 

 of inefficient pasteurization treatments 

 due to defective mechanical design or 

 of improper operation of the unit. At- 

 tention has already been called to the 

 more important of these possibilities 

 in another section of the report. These 

 samples are all in addition to those col- 

 lected for the direct determination of 

 pasteurization efficiencies. The latter 

 should include the following and as 

 many more as may be necessary to 

 give a thorough picture of the effective- 

 ness of each step and stage in the oper- 

 ation : Samples of the raw milk at the 

 very start of the run and at the very close 

 and one or more in between depending 

 upon the history of the milk under 

 treatment; samples of the first, last 

 and several intermediary in the run of 

 the milk after heating and before hold- 

 ing; the same after holding .and be- 

 fore cooling and if there are several 



steps in this portion of the operation 

 then samples from each should be 

 taken ; the same after cooling and 

 before passing into the can or bottle 

 fillers, also after leaving the fillers and 

 before entering the cans or bottles and 

 finally from the cans and bottles. The 

 samples of the product in these later 

 steps in the process are to be collected 

 and tested with the object of determin- 

 ing the possibilities of reinfection of the 

 already heated and held milk. 



All such samples should be subjected 

 to the standard procedures of the Lab- 

 oratory Section of the A. P. H. A. for 

 the bacteriological examination of milk 

 for total counts and for the quantita- 

 tive determinations of B. coli by the 

 standard methods of bacteriological 

 examination of water of the same Sec- 

 tion. 



Interpretation of Results on Tests of 

 Efficiency. When the results on the 

 cleanliness samples do not show the 

 absence of B. coli in one c. c. tests of 

 all drips and condensations and wash 

 waters, and very small numbers of 

 bacteria or none at all, the cleaning 

 and sterilizing processes should be con- 

 sidered as deficient. When the results 

 of the tests of the samples of the milk 

 from the holding system indicate the 

 presence of B. coli in 1 c. c. inocula- 

 tions, further or careful and critical 

 study of operations of each step and 

 stage in the pasteurization process are 

 called for. When the results of the 

 tests of the samples taken at any stage 

 after the holding show the presence of 

 substantially larger total counts of the 

 presence of larger numbers of B. coli 

 than were found in comparable samples 

 of the milk from the holding system, 

 reinfection of the milk is indicated and 

 the cause or causes of the same should 

 be ascertained by further study. 



(5) Conclusions on the Analytical 

 Control of Pasteurization Plants. It 

 is evident that the analytical control 

 of pasteurization plants calls for the 



