Pasteurization of Mil'k 



17 



correct charts, revolve eccentrically, 

 not adapted to this form of recording, 

 recording lines may be too heavy, too 

 light, may be blurred, poor paper, poor 

 ink, difficulty of adjustment, easily 

 faked by spinning of chart, by falsely 

 adjusting pen. 



(2) Chemical Methods. No purely 

 chemical test capable of differentiating 

 between pasteurized and unpasteurized 

 milk have as yet been developed to a 

 satisfactory point and certainly none 

 have been presented which would give 

 results which would warrant any con- 

 clusion that an appropriate heating as 

 to time and degree had or had not been 

 applied. 



(3) Physico - Chemical ]\lethods. 

 While Frost and others have presented 

 methods for determining by micro- 

 staining reactions whether a given 

 sample of milk has been subjected to 

 a heating process, such procedure-^ 

 have been far from giving results which 

 could be utilized in even estimating 

 the degree of temperature attained or 

 the duration or the thoroughness of its 

 application and yet upon these factors 

 rests the efficiency of all pasteurization 

 processes. 



(4) Biological Alethods. In any sys- 

 tem desig'ned to meastire accurately the 

 effectiveness of the pasteurization proc- 

 ess, the main and special object of the 

 elimination of disease-producing para- 

 sites as distinguished from the reduc- 

 tion in numbers of bacteria must al- 

 ways be kept to the front. Failures to 

 g-ive proper relative values to these 

 two results occur commonly by reason 

 of the past general utilization of the 

 count of the total number of bacteria 

 m a cubic centimeter of a raw milk as 

 an adequate measure of the sanitary 

 quality of that product. However, the 

 almost insuperable difficulties sur- 

 rounding any attempt at testing a 

 practical system by the use of milk ac- 

 tually innoculated with pathogenic 

 bacteria, has left the investigators in a 



degree of uncertainty with no choice 

 but to interpret the results of approp- 

 riate tests on the forms of bacteria 

 commonly found in milk in the light of 

 the probable effects on those having 

 the power of producing disease in man. 



The usual biological determinations 

 aim, therefore, at the demonstration 

 of the direct and indirect effects on the 

 degree, duration, and thoroughness, of 

 the heating and cooling operations 

 upon the bacterial flora of the raw 

 product. 



In view of the relatively large 

 amounts of milk handled even in the 

 very shortest operative runs of even 

 the smallest forms of practical pasteur- 

 ization systems, it is obvious that sub- 

 stantially all control observations must 

 be made while the system is in prac- 

 tical use — that is, the demonstrations 

 of efficiency involving tests of the 

 product, must be made upon the milk 

 as it comes to the plant in the regular 

 course of business, although this tends 

 to introduce a considerable number of 

 variable factors by reason of the mul- 

 tiplicity of experiences and vicissitudes 

 through which the raw milk may have 

 passed which may have affected its 

 bacterial flora. 



(aj Biological Demonstrations of 

 Efficiency, Procedure A. 



A. Comparison made between the 

 counts of viable bacteria in the raw and 

 the pasteurized and cooled milks, sup- 

 plemented by similar bacterial counts 

 at various important intermediary 

 stages. 



These comparisons are frequently 

 expressed in terms of percentage re- 

 ductions in numbers of living, i. e., 

 viable bacteria on the usual culture 

 media. 



Ayers and others have called atten- 

 tion to some of the fallacies involved 

 in the use of this system of percentage 

 reduction in numbers of living bac- 

 teria, as a means of judging the effi- 



