Basic Principles of Operation

Pasteurisation draws its principles and its name from the work of Louis Pasteur (1822 - 1895) the famous French chemist who was instrumental in establishing industrial microbiology. He demonstrated that the souring of milk was similar to the spoilage of wines and beers, which he had already determined was caused by the growth of undesirable micro-organisms.

As well as the spoilage organisms, he found it was necessary to destroy pathogenic bacteria such as Mycobacterium tuberculosis and Brucella to stop the spread of these diseases. Pasteur achieved this by heating to a certain temperature and holding at this temperature for a period of time before cooling down to a suitable temperature for storage.

The batch pasteurisation process originally developed commercially required that milk should be held at not less than 62.8ºC and not more than 65.6ºC for at least 30 minutes and immediately cooled to not more than 12.8ºC. Dahlberg (1932) presented a definitive comparison of the time / temperature combinations required to inactivate Mycobacterium tuberculosis and it was shown that higher temperature and shorter times give similar results

Shorter holding times allow continuous flow systems to be used and these systems in modern day industrial use are termed High Temperature Short Time process or HTST. The regulations in the United Kingdom allow heat treatment at 71.7ºC for 15 seconds followed by cooling to not more than 8ºC

The HTST system effectively superseded the holder system because of its practical advantages for large scale operation

The Armfield Ltd Laboratory Pateuriser has been designed to accurately reproduce the industrial HTST process on a miniature scale requiring only small quantities of raw material to carry out thorough and meaningful experiments. Nominal throughput is only 10 litres / hour

The heat exchanger has been designed to allow incoming cold product to be preheated by out going pasteurised product. This heat recovery feature enhances the economic efficiency of the process

As this is a laboratory pasteuriser, temperatures and holding times can be easily adjusted to give product of varying qualities. Samples are taken for biological analysis and a continuous computer printout of relevant temperatures enables the student to produce all information required for a detailed study of the process. All this can be achieved within a normal 3 hour laboratory period