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A technique has been developed for production of a stable suspension of spores of Bacillus stearothermophilus var. calidolactis. The organism was grown in a sporulating medium on a rotary shaker at 55°C. After 4–5 d, spores were centrifuged and washed to obtain a clear spore suspension, which was able to detect as low as 0.008 I.U./ml of penicillin in 2 h. The spore suspension retained its viability up to 5 months.

Butter samples treated with potassium sorbate and sodium chloride were analyzed weekly for bacteriological qualities after storage at different temperatures. Addition of 0.1% potassium sorbate and incorporation of 2% sodium chloride plus 0.1 percent potassium sorbate resulted in inhibition of mold growth in all the samples at the end of 4 weeks at 18 C and 5 C. However the effect of potassium sorbate alone was less pronounced, irrespective of storage temperature. As regards coliform count in control butter, it increased rapidly at 22 C, but decreased when butter was stored at 5 C or – 18 C. Addition of potassium sorbate to butter samples stored at 18 C reduced the coliform count to zero after 4 weeks. while butter with added potassium sorbate and sodium chloride showed a zero count after 1 week, indicating a cumulative inhibitory effect.

Potassium sorbate was incorporated at the rate of 0.1% in a lot of butter at the time of working. Samples of butter were analysed each week for 6 weeks for mold, coliform bacteria, free fatty acids and thiobarbituric acid values after storage at different temperatures (20 C, 27 C, 37 C). Potassium sorbate inhibited the mold in all the samples at the end of 5 weeks at −20 C. Coliform counts increased rapidly in control samples at 37 C; however, consistently lower coliform counts were recorded in the butter samples containing potassium sorbate.

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