The Problem of Transporting Milk in Hot Condition

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Abstract
Since glass-lined tanks mounted on railroad cars and auto- mobile trucks have come into use for the transportation of milk, the question has again been raised as to whether milk could not be heated and kept hot during transportation and bacterial growth checked by heat rather than by refrigeration. This is a logical question for an engineer to ask, for he is not expected to have any knowledge of the thermophilic types of bacteria. (The term thermophilic is used in its correct sense, meaning bacteria which grow at high temperature.) But the bacteriologist will at once think of these bacteria and will question the practicability of shipping the milk hot. However, even though we admit there are thermophiles in milk, we can not tell in ad- vance what their action will be or how quickly they will act, without actual data on the subject: For this reason we wish briefly to report the results of a few experiments. As early as 1867 Muller (4) while studying the influence of temperature on milk souring found that milk held at 50°C. (122°F.) became sour and appeared greenish-yellow, the same as at 35°C. (98°F.). He came to the conclusion, however, that at 50°C. (122°F.) the souring appeared to be due to a different kind of fermentation from that at lower temperature, and that it should be investigated. Leichmann (3) in 1894 found that milk coagu- lated after twelve to fifteen hours when held at 50°C.(122°F.) and that a fine coagulum appeared. He pointed out that this fermentation was not due to the ordinary milk-souring organism. These fermentations were undoubtedly due to thermophiles, which under favorable conditions may develop and play an im- portant rSle in the changes that take place in the milk and 608

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