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D Value And Z Value Calculator

Work out d value and z value instantly with clear inputs, formula shown and shareable results.

About D Value And Z Value Calculator

The z value is the temperature change that alters the D value tenfold: z = (T2 - T1) / log10(D1/D2). A z of 10 C means each 10 degree rise cuts D by a factor of ten. Vegetative bacteria typically show z of 4-8 C and bacterial spores 8-12 C, which is why spore destruction needs retort temperatures.

Formulas

z value

z = (T2 - T1) / log10(D1 / D2)

Rate factor

Rate increase per 10 C = 10^(10 / z)

Worked example

With the default values below, D Value And Z Value Calculator returns z Value of 10.0000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Time At First Temperatureminimum 0 minutes
10 minutes
First Temperatureminimum 0 degrees C
60 degrees C
Time At Second Temperatureminimum 0 minutes
1 minutes
Second Temperatureminimum 0 degrees C
70 degrees C

Results

z Value
10.0000
Log Ratio Of D Values
1.00000
Temperature Difference
10.00
Rate Increase Per 10 Degrees
10.0000

Step by step

  1. 1Values used
  2. 2z value
  3. 3Rate factor
  4. 4z Value= 10.0000
  5. 5Log Ratio Of D Values= 1.00000
  6. 6Temperature Difference= 10.00
  7. 7Rate Increase Per 10 Degrees= 10.0000

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • D and z values must be determined for the specific organism and food matrix. Using literature values without confirmation can lead to an unsafe process.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

D and z values must be determined for the specific organism and food matrix. Using literature values without confirmation can lead to an unsafe process.

Frequently Asked Questions

Why do D and z both matter?

D fixes how long a given temperature takes to achieve a tenfold reduction; z fixes how much faster a higher temperature works. Together they allow any time-temperature combination to be compared for equivalent lethality.

Can z be extrapolated widely?

Only with care. The log-linear relationship generally holds over the range tested but can break down at extremes, and shoulder or tailing behaviour invalidates simple first-order treatment.

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