A Comparison of the Bactericidal Efficiencies of Laboratory Holder and HTST Methods of Milk Pasteurization and the Keeping Qualities of the Processed Milks

SUMMARY The in‐place sterilization of a laboratory‐scale HTST milk pasteurizing plant and its use for the aseptic treatment of milk samples are described. Comparisons of the effect of laboratory pasteurization by holder and HTST methods on the bacterial content of milk and its keeping quality after pasteurization have been made. Experiments using sterile milk inoculated with specific test organisms showed the HTST treatment to have a greater bactericidal effect than the holder treatment against a strain of Pediococcus but with a Streptococcus strain the reverse was true. However, pasteurization of naturally infected milks from different sources showed that, in practice, both treatments yielded similar results as indicated by the relative proportions of bacteria destroyed and the keeping qualities of representative samples incubated at 22°C after pasteurization.