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Calculate an equivalent heat process at a higher (or lower temperature) knowing the z-value and the F (P) value at the reference temperature

 There will be occasions when a food manufacturer wishes to use a different, but equivalent lethal thermal process. How does the processor calculate the equivalent process?

This article explains how to calculate an equivalent thermal or heat process at a higher or lower temperature and provides access to a free On Line calculator for checking your calculations.

Providing that the F value at Tref and the z value are known then the F value at the required temperature, T, can be calculated using equation 1.

Equation 1.  


Equation 1 has been derived from Stumbo (1973).

 An example of how to use equation 1 is given for a fruit drink product.  The product was previously produced using a Tref of 85°C and a holding time of 15 minutes.  The processor has installed a continuous pasteurizer and wishes to use a temperature of 102°C to produce the drink. Calculate the holding time at 102°C, that will give an equivalent lethality to 85°C for 15 minutes given the z-value is 8.7°C.

We will use equation 1 to do the calculation. Firstly breaking down the terms in the equation, we will first calculate:


     = -1.954

Going back to equation 1 we can now insert the -1.954 we have calculated.

Finally, we can add the value for Fref and complete the calculation.

F = 0.167 minutes or 10 seconds.

The same equation and approach to the calculation can also be used to calculate equivalent process lethality at a lower temperature.

Note this approach should be used carefully since the linearity of the D-values (implied in the calculation) may only apply over a limited range of temperature.

Go to the Thermal process equivalence calculator

Literature cited

Stumbo, C. R. (1973). Thermobacteriology in food processing, 2nd ed. Academic Press, New York.

How to cite this article

Mullan, W.M.A. (2016). [On-line]. Available from: https://www.dairyscience.info/index.php/thermal-processing/302-equivalent-process.html . Accessed: 24 October, 2016.

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