Thermal Death Time Calculator

Work out thermal death time instantly with clear inputs, formula shown and shareable results.

About Thermal Death Time Calculator

Thermal death follows first-order kinetics: each D value of holding time reduces the population tenfold. Time required is the log reduction needed times the D value at the process temperature, less any lethality already accumulated during come-up. A 6-log reduction needs 6 D values.

Formulas

Thermal death time

Time = log10(N0 / N) x D value

Survivors

N = N0 x 10^(-time / D)

Worked example

With the default values below, Thermal Death Time Calculator returns Hold Time Required of 2.7000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Initial Microbial Countminimum 1 CFU/g: 1,000,000 CFU/g
Target Surviving Countminimum 0 CFU/g: 1 CFU/g
D Value At Process Temperatureminimum 0 minutes: 0.5 minutes
Lethality Credited To Come-Upminimum 0 minutes: 0.3 minutes

Results

Hold Time Required: 2.7000
Total Lethality Required: 3.0000
Log Reduction Required: 6.0000
Predicted Survivors: 1.00000000

Step by step

1Values used
2Thermal death time
3Survivors
4Hold Time Required= 2.7000
5Total Lethality Required= 3.0000
6Log Reduction Required= 6.0000
7Predicted Survivors= 1.00000000

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 8 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Thermal process design is food safety critical and must be established by a competent process authority using validated D and z values for the target organism.

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

Thermal process design is food safety critical and must be established by a competent process authority using validated D and z values for the target organism.

Frequently Asked Questions

Where do D values come from?

From thermal resistance studies on the specific organism in the specific food matrix. D values vary greatly with pH, water activity, fat content and prior stress, so generic values are not adequate for validation.

Why is a 6-log reduction the common target?

It is the conventional performance standard for pathogen reduction in many regulations, chosen to bring realistic initial contamination to a negligible probability of a surviving cell.