Canned food is sterilized to kill bacteria and their spores. The number of bacteria and spores killed during sterilization of a can depends on
- the temperature at which a can is heated, and
- the length of time a can is heated.
The higher the temperature and the longer the heating time, the greater the number of bacteria and spores killed. The exact relationship between the length of time a temperature is used to sterilize a can and the resulting kill rate of bacteria and spores can be determined using a mathematical formula known as the F-value.
The F value is the result of a calculation and therefore a measure of the number of bacteria and spores killed during sterilization of a can. To prevent the canned goods from becoming inedible due to excessively high temperatures, sterilization to F-value can be used to achieve the same result as cooking at a higher temperature but for a shorter time by extending the sterilization process at a lower temperature.
To be on the safe side when determining the sterilization temperature, the temperature must be determined at the most thermally unfavourable point of each container, i.e. at the coldest point. In a can of cooked sausage meat, for example, this is the geometric center, which lies exactly in the middle of the can. The temperature sensor must therefore be located here.
The temperature 121.1°C (equivalent to 250°F) is a standard temperature with regard to the F-value. If a can is heated for 1 minute at exactly 121.1°C, the F value is 1.
Of course, the quality of the canned food before the sterilization process begins is essential for a sterilization process. If the quality of the canned food is poor at the start of the sterilization process, i.e. it has a high initial bacterial content, top quality cannot be achieved even by sterilization using a corimat.