Samples of sterilized milk from fifteen dairies in the Midlands have been examined, and seasonal variations were detected in the incidence of mesophilic and thermophilic sporeformer contamination. Seasonal variation in the rate of spoilage at 30° C. was also apparent.The lower incidence of contamination in summer was considered to be due to (a) less sporeformer contamination during milk production at the farm in the period when the cattle are not housed, and (b) increased processing times and temperatures in warm weather.Cleansed milk bottles were examined and found to be an important source of contamination by mesophilic sporeformers, but the incidence of thermophiles of the type commonly found in sterilized milk was low.Methods of reducing contamination in sterilized milk were discussed.

Cultures of sporeforming bacteria isolated from commercially sterilized milk were examined and seasonal variations in the incidence ofB. subtilis/B. licheniformisstrains were apparent which may account for the increased rate of spoilage at 30° C. during the winter.B. subtiliswas the most common mesophilic sporeformer isolated, and under favourable conditions it produces rapid digestion of milk.Thermophilic sporeformers are frequently present, and usually produce a firm acid clot in milk held at temperatures favourable for their growth. The classification of the thermophiles isolated is uncertain and a review of the classification of the aerobic thermophilic sporeformers in general is required.Cl. thermosaccharolyticum, a gas-producing thermophile, was isolated from sterilized milk.