Z Value in Steam Sterilization

Z-value is the number of degrees the temperature is required to change a D-value one factor of ten (a 10-fold variation in the D-value). 

The z-value is considered as 10°C for the temperature range from 100 to 130°C for steam sterilization.

Z Value Calculation

Calculating a Z-value graphically is relatively easy. Plot at least 3 D-value/temperature pairs on a semi-logarithmic graph and, using your best judgement, draw a straight line through the points that most closely fits the data. From this line, determine the number of degrees required to change the D-value by one factor of 10 (see the below figure).

In the above case the Z-value appears to be approximately 8°C.

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