Z-value

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For Z-scores in statistics, see standard score.

Z-value of an organism is the temperature, in degrees Fahrenheit or Celsius, that is required for the thermal destruction curve to move one log cycle. While the D-value gives us the time needed at a certain temperature to kill an organism, the z-value relates the resistance of an organism to differing temperatures. So, the z-value allows us to calculate a thermal process of equivalency, if we have one D-value and the z-value. So, if it takes an increase of 10°F to move the curve one log, then our z-value is 10. So then, if we have a D-value of 4.5 minutes at 150°F, we can calculate D-values for 160°F by reducing the time by 1 log. So, our new D-value for 160°F is 0.45 minutes. This means that each 10°F increase in temperature will reduce our D-value by 1 log. Conversely, a 10°F decrease in temperature will increase our D-value by 1 log. So, the D-value for a temperature of 140°F would be 45 minutes.

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