THE EFFECT OF SEASONAL VARIATION AND CONDITIONS OF MILK PRODUCTION ON THE BACTERIOLOGICAL QUALITY OF REFRIGERATED FARM VAT MILK SUPPLIES

Abstract

SUMMARYThe bacterial content of daily collected refrigerated farm vat milk from 94 farms in a traditionally dairying district in South Wales was appreciably higher during summer than in winter. This applied to total colony count, thermoduric count and coli‐aerogenes organisms content all determined at 30°C, and even to resazurin reduction in 2 h at 37°C.The type of milking plant and different methods of in‐place cleaning had quite a marked effect on the bacterial content of the milk. Milk from farms with cowshed pipeline milking plants had a much higher bacterial content than milk from farms with parlour pipeline plants.The results obtained with the acidified boiling water method of in‐place cleaning were distinctly better than those obtained with circulation cleaning. The highest total colony counts and coli‐aerogenes counts for the milk supplies were associated with unsatisfactory methods of circulation cleaning.Unsatisfactory cleaning of bulk milk vats was associated with a high coliaerogenes content in the milk from a few farms; it is possible that psychro‐trophic coliforms are derived from this source. Milk from 5 of the 6 farms where tanks were automatically cleaned had consistently low thermoduric counts.