Microbiology (continued)

UHT milk was introduced to Australia at the end of the 1950s. This milk is flashed up to about 135^oC for a very short time (2-3 seconds), crash cooled and aseptically filled into cartons. In unopened cartons it keeps at ambient temperatures for 5-6 months. The method is valuable for fruit juices and fruit drinks also.

The introduction during the 1950s of tanker collection of milk from refrigerated vats on farms greatly improved the microbiological quality of milk but brought with it a new microbiological hazard, psychrotrophic organisms which grow at refrigeration temperatures (2-7°C). Non-pathogenic, these organisms are destroyed by pasteurization but they induce unwanted flavours and thus impose an unexpected constraint on a technological change; increased incidence of psychrotrophs has influenced the length of time for which milk may be satisfactorily held at refrigeration temperatures and has imposed tighter controls on the industry.

Food microbiology was almost non-existent in Australia before the Second World Wan As noted, only one or two companies practised it and W. J. Scott who began CSIR's work in this area was appointed only in 1933 -as a biochemist![171] Specific training was hard to get, as all bacteriology then taught in Australian universities was taught if not within at least to support medical and veterinary faculties. Melbourne's first professor in the discipline was appointed in 1935.[172] Scott's, Shew's and Christian's first degrees were in Agriculture, the microbiological content of which had caught their imagination. More general training has become available only since the Second World War and while there is still a long way to go to accomplish the desired degree of microbiological surveillance, there is a greater realization by the Australian food industry that microbiological support is essential, and more people with at least some training in microbiology are being employed in it. The thorough cleaning of the whole plant, its treatment with antiseptics (sanitization) and the importance of the personal hygiene of plant operatives have been emphasized in special courses. Aseptic packaging has been introduced and treated filtered air is supplied under positive pressure to some rooms in which sensitive products are packaged without heating.

The major Australian contribution to food microbiology has been Scott's classic demonstration that it is not the water content but the water activity of a food system which governs microbial growth and toxin production. Scott's work was expanded by his colleague, J. H. B. Christian, and it has had a profound impact on food technology.[173] The understanding and control of water activity has contributed to the better storage of foods generally and is the basis of much modern food formulation, especially of intermediate moisture foods such as certain types of sausage.

Australian Academy of Technological Sciences and Engineering