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    1. Hi Naresh!

      Thanks for your query. Actually, it differs for different micro-organisms. But, when we don’t know exact details, we can consider the z-value as 20°C since you mentioned DHS even at 220°C. If you’d have said moist-heat sterilization (steam sterilization), we then should consider the z-value as 10°C when we don’t know exact microbe details to deal with.

      Or you can determine the z-value as
      1. Determine the D-value of an organism at min. 3 to 4 different temperatures.
      2. Construct a death curve by plotting the log D vs. temperature.

      I hope this clarifies. Please do not hesitate to ask for any additional information and I would be more than happy to respond.

  1. When calculating with a different program, two values were obtained: Fh=13.78(min) and Fh=0.07(min).
    0.07(min) could be obtained in the same way as your writing, but I have no idea how 13.78 is calculated. Do you happen to be able to seek advice?

    1. Hi Jeon!
      Glad to see you. It’d be great if you share more details on this. What are the parameters you are dealing with? This will help me to understand and elaborate on what might be the cause.

      1. Parameters:
        Z = 10
        Tref.℃ = 121℃.
        The duration is 25 minutes and the average temperature is 119.41℃.
        The resulting values were Fh=13.37 and Fh=0.07(min). Please let me know if you need any more information.

        1. Hi Jeon!
          Thanks for getting back. I see your parameters resonate with steam sterilization as Z=10 and Avg. Temperature is 119.41℃ @ 25 mins.
          This particular page discusses dry heat sterilization where the Z-value is assumed as 20℃. So, first of all, you should use the F0 value.

          Now coming back to your values & considering this as steam sterilization, the F0 value for this scenario would be around 17 mins. Use this link instead I would suggest!

          Let me know if this helps.

          1. Oh, I understand. Thank you.
            But when you experiment with steam sterilization at 121℃,
            Can’t I get the Value of Fh?
            ‘Fh’= Is it a Dry Heat Sterilization?

          2. The F0 value also called Equivalent Exposure Time is used for Steam Sterilization. The Fh value also called Heat Penetration Factor is used for Dry Heat Sterilization. You can’t mix them because their purpose is different. You can read above the tabulated differences.
            Hope this clarifies!

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