Milk storage and microbial growth

It is common practice to collect milk of several milkings in a bulk tank before transportation of the milk to the dairy (e.g. milk of about four milkings in the UK and milk of six milkings in the Netherlands). To prevent microbial growth in the farm bulk tank, milk has to be cooled during storage. The European Union requires cooling of bulk tank milk to a temperature below 8 °C when milk is collected daily, and to a temperature below 6 °C when milk is not collected daily. However, cooling of milk does not prevent the growth of microorganisms completely. Some psychrotrophic organisms, such as Pseudomonas spp. and L. monocytogenes, still grow at temperatures below 6 °C, although at reduced rates. Modelled studies showed that, in adequately functioning bulk tanks, the concentrations of psychrotrophic L. monocytogenes and B. cereus will not increase significantly.