EU legislation indicates that total bacterial count (TBC) in milk should be less than 100,000/ml. However, ideally and on many farms, a TBC of less than 15,000/ml can be reached. Thermoduric bacteria counts of greater than 1,000/ml are generally penalised. However, ideally this count should be less than 200/ml.
Thermoduric bacteria can survive exposure to temperatures considerably above their maximal temperature for growth. In the dairy industry, the term is applied to those organisms which survive, but do not grow, at pasteurization temperature. They usually include species of Micrococcus, Streptococcus, Lactobacillus, Bacillus, and occasionally gram-negative rods. The sources of contamination are poorly cleaned equipment on farm. These bacteria contribute to significantly higher Standard Plate Count on pasteurized milk (LPC counts). The thermoduric count has been used in the dairy industry as a means of detecting sources of organisms responsible for high counts in the final product.
In the dairy industry, the term thermophilic bacteria applies particularly to bacteria which grow in milk held at elevated temperatures (55 C or higher), including pasteurization, 62.8 C. The species that grow in higher temperatures include Bacillus species which enter milk from various sources in the farm, or from poorly cleaned equipment. When the milk is held at high temperatures for long periods, these bacteria rapidly increase in numbers and may cause taint defects or problems with respect to bacteria standards.
The microorganisms which play a significant role in biological processes in low-temperature environments have usually been called psychrophilic, meaning cold-loving. Psychotropic is used to refer to the bacteria that are able to grow rapidly at 7 C and below. Species of Pseudomonas, Flavovacterium, Alcaligenes, Acinetobacter, and Bacillus are often encountered among psychotropic group. These group of are generally non-pathogens, but in dairy products they can cause a variety of taints, including fruity, stale, bitter, putrid and rancid taints. Psychotropic bacteria are rarely present in the udder. The numbers of bacteria depend upon sanitary conditions prevailing during production and upon time and temperature of milk storage before processing. The influence of psychotropic bacteria in the shelf life of pasteurized milk will depend mainly upon the number present after packaging, the rate of growth, the storage period, and the biochemical activity of the organisms.
The simple answer for avoiding these organisms is sanitation!!!!