The F-value is a measure of the thermal load on food during cooking or processing. It indicates how much heat energy is absorbed in a food within a certain period of time.
The F-value is given in units of minutes x degrees Celsius and is generally used when steam sterilizing food. It is calculated by knowing the temperature and duration of the heat treatment in a particular food.
The formula is: (F = D (\log N_0 – \log N))
The F-value provides information on how deeply the thermal stress penetrates into the food and how intensively it has been processed. A higher F-value means that the food has been exposed to a higher temperature for longer and has therefore been processed more intensively. A lower F value, on the other hand, means that the food has been subjected to less thermal stress and has therefore been processed less.
The F value is used in the food industry to ensure that food is processed sufficiently to kill potential microorganisms that can lead to food spoilage or intoxication without causing too much damage to the food. It can also be used to monitor the quality of food during processing and storage.
Two methods can be used to obtain a final F value. The first option requires the core temperature to be recorded as a curve using a temperature recorder. This curve is divided into minute intervals in the range above 55 degrees Celsius. The entire temperature curve above 55 degrees is decisive. This includes the time until the temperature falls below 55 degrees again during cooling. Each time interval is now assigned the F value corresponding to the temperature value and added up continuously. The addition results in the final F-value. This method is only used if you want to check the progress of a cooking process.
A second option is the use of microprocessors. These devices use a core temperature sensor to register the temperature curve during the cooking process and automatically calculate the F value reached. With these control units, it is also possible to control a final F-value and stop the cooking process based on this criterion. This type of F-value cooking is standard with our controls.
A recommendation on the F-value to be achieved states that this should be 40. This recommendation is based on the following values:
In practice, this reduction in the number of germs means that 99 out of 100 products are germ-free and that one piece still has a germ.
Since cooking according to the core temperature is already known and it seems much more complicated to determine the F-value, this question is understandable. In our opinion, setting a specific final core temperature value, as is done in many places today, does not always make sense. Due to the diverse range of products, the different calibers, the different product dimensions, the varying product weights and, last but not least, the different thermal conductivity values, the same core temperatures produce different results in terms of shelf life and the killing of microorganisms. Based on experience in canning, it is obvious that the F-value is the decisive factor. The problem is that different final core temperature values must be used for each caliber, dimension, weight, etc. in order to achieve the same F-values. This is virtually impossible, even with today's control systems.
The microorganisms on which the calculations are based, in particular the D-streptococci, are killed from a temperature of 55 degrees Celsius. This means that the total number of germs is reduced at temperatures above 55 degrees Celsius. Depending on the level of this temperature reached, a corresponding F-value is achieved per unit of time of one minute. The following values are important for the F-value of pasteurization:
