Just a few minutes of too-low temperatures can make the difference between a sterile product and one that is potentially dangerous. It is also vital to find the coldest point in the product during heating and to measure the temperature there so that the lethal effect on bacteria can be calculated. Pressure and pack-bulge readings are sometimes also necessary in order to validate safety. Several of the companies we work for export their products and some countries, such as the USA, have stringent requirements about the documentation that must be carried out.
When taking readings inside microwave ovens and similar it can be difficult to use traditional methods because metals cannot be used. One must often use several methods in combination. The aim is to carry out controlled trials on a laboratory scale and then to upscale these to larger catering ovens and then to full scale industrial ovens. The temperature distribution is also unpredictable, necessitating the use of more measuring points than for products that are heated in ovens or autoclaves, for example.
The documentation is therefore prepared through a combination of biological time-temperature integrators (TTIs), infra red (IR) cameras and optical temperature sensors. This involves the use of alginate pellets that are fed with a known concentration of bacteria.
With heat treatment corresponding to pasteurisation or lower, we know that harmful bacteria of the types Clostridium and Bacillus may survive to a certain extent and become a potential risk in the product. In most pasteurised products we are looking for a safety level of 6D (a reduction by 6 logarithmic units) of the illness-causing bacteria. This is not always possible since the sensory properties can be spoiled. In the development and production of minimally treated foods therefore the aim is to calculate the lethal effect on such harmful bacteria and build up knowledge of the vital factors 1) survival 2) germination and 3) growth in the products. Each of these factors will vary depending on the method of heat treatment used and the raw materials and ingredients involved.
