# How to Calculate T Value

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```					CALCULATION OF STERILIZING VALUES
This spreadsheet contains two usable functions:
Function gValue calculates the residual temperature difference g = Th-T from the sterilizing value U (equivalent time at Th) and pro
Function Uvalue calculates the sterilizing value U (equivalent time at Th) from the residual temperature difference G and process pa
Reference:
Pham, Q.T., 1987, "Calculation of thermal process'lethality for conduction-heated canned foods". J. Food Sci. 52: 967-974.

Example 1 of Pham's paper
Calculate sterilizing value U from the following data:

Symbol         deg.F         deg.C       Units    Meaning
Ti            160        71.1   F or C   Initial product temperature
Th             230       110.0   F or C   Temperature of heating medium
Tc              50        10.0   F or C   Temperature of cooling medium
z             16         8.9   F or C   Temperature change that will cause a tenfold change in the sterilization rate
f             55          55   mins     Time for residual temperature difference to be reduced by a factor of 10, assuming l
j             2           2   -        Lag factor at centre for heating or cooling: (Th-T)/(Th-Ti) = j.10^*(time/f)
t            169         169   mins     Heating time

Results of calculations:
g        0.118   0.066 F or C             Residual temperature difference, Th-T, at the end of heating
U #NAME? #NAME? mins                      Sterilizing value at centre of can

Example 2 of Pham's paper
Calculate required temperature difference at end of heating, g = Th-T, from the following data:
Symbol deg.F             deg.C      Units      Meaning
Ti         140       60.0 F or C      Initial product temperature
Th          240      115.6 F or C      Temperature of heating medium
Tc           60       15.6 F or C      Temperature of cooling medium
z          18       10.0 F or C      Temperature change that will cause a tenfold change in the sterilization rate
f         195        195 mins        Time for residual temperature difference to be reduced by a factor of 10, assuming l
j         1.8       1.8 -           Lag factor at centre for heating
jc            2          2-           Lag factor at centre for cooling
U          16.2      16.2 mins        Heating time

Results of calculations:
g #NAME? #NAME? F or C                    Residual temperature difference, Th-T, at the end of heating
sterilizing value U (equivalent time at Th) and process parameters
esidual temperature difference G and process parameters

anned foods". J. Food Sci. 52: 967-974.

e a tenfold change in the sterilization rate
ence to be reduced by a factor of 10, assuming logarithmic heating/cooling
ooling: (Th-T)/(Th-Ti) = j.10^*(time/f)

h-T, at the end of heating

e a tenfold change in the sterilization rate
ence to be reduced by a factor of 10, assuming logarithmic heating/cooling

h-T, at the end of heating

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