z-value

The temperature change needed to change the D-value by a factor of 10. If an organism's z-value is 10 °C, raising the temperature by 10 °C makes it ten times faster to kill. The z-value lets you convert time at one temperature into equivalent lethality at another, which is the basis of F₀ calculations. By convention, 10 °C is used for steam F₀ calculations and 20 °C is common for dry heat.