The Principles of Canning for Fishery Products: Calculating Fo Values

Thermocouple probe

To be sure of commercial sterility the Fo value at the SHP, the thermal centre of the container, must be sufficient to kill all Clostridium botulinum and reduce survival probabilities for other more heat resistant bacteria to an acceptable level. It is assumed that bacterial spores will randomly contaminate the fish and that therefore they may be located at the SHP. Although a pessimistic approach, this caters for the ``worst case`` scenario on which product safety must be based.

The measure Fo value heat penetration studies are conducted for representative packs of the canned fish filled to the maximum fill weight likely to be encountered. These cans are then fitted with thermocouple probes which must be located so as to measure the temperature at the SHP. (As can-to-can variation in the rate of heat penetration can be significant, it is recommended that at least twelve replicates are tested before data from the slowest heating of all the test cans are used to compute the Fo value for the process).The thermocouples are connected to digital or graphical recorders, some of which indicate the product temperature during the thermal process, while others can be purchased which automatically compute Fo value. Where automatic computation is not possible, the temperature-time data can be used in a number of ways to calculate Fo value.

Figure 2. Thermal death time curve passing through 1 min at 121.1 ºC

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