An investigation into a modified Tyndallization process for the reduction of heat resistant sporeforming organisms in milk and cream was carried out. This involved two heat treatments separated by a period of anaerobic incubation. Laboratory experiments were performed on both mixed and pure populations of sporeforming bacteria, and a plant experiment on the natural sporeforming flora of 18 per cent cream. No evidence of any worthwhile reduction of these organisms was found.

Single cream was pasteurized over the range 74°­81.5°C (16S°­179°F) for 15 s and 80°­90°C (176°­194°F) for 1 s. packed aseptically and stored at 7°C. The longest shelf life was obtained when either the time or the temperature was at the minimum consistent with adequate pasteurization. The shorter shelf lives obtained at higher temperatures of pasteurization were attributed to the effect of heat activation on the spores of Bacillus spp, which were then capable of germination and outgrowth at 7°.

The comparative microbiological shelf‐lives of skimmed, semi‐skimmed and whole milks were studied under controlled conditions. No difference in shelf‐life between the milks was observed whatever the conditions of storage or contamination. The factors that were established to affect shelf‐life, irrespective of fat content, were the presence or absence of post‐pasteurization contamination and the temperature of storage.

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