Canning and Fish Packaging Technology

4.8.1.Calculation of Fo value

Unit 4 - Thermal process for canned foods

4.8.1.Improved general method of process calculation (Calculation of F_o value)

Since general method is laborious and not well suited for routine calculations, Shultz and Olson (1940) introduced further modifications based on ball’s concept of hypothetical microorganism which has a Z value of 18F^o or 10C^o (as for Cl. botulinum) and it passes through the point of 1 minute at 250^oF. He also gave the equation to calculate lethal rate i.e., Lethal rate = 1/Antilog (250-T/Z) in the case oF is used and when measurements in ^oC is used it is L.R = 1/Antilog (121.1-T/Z)

Because of this equation, lethal rate can be calculated for all other temperature. To illustrate significant contribution of Ball described above, it is seen from the TDT curve of Cl. botulinum, TDT (F value) is 2.45 min at 121.1^oC while at 113^oC it is 10 min. Therefore, 1 minute at 113°C is equivalent to TDT of 0.245 min (F value) at 121.1^oC. By improved general method, both Fo value of the process as well as process time required can be calculated.