GIFSQ Tools · Module 3 — Food Microbiology & Enumeration · Tool 048 of 500
Measure how much a treatment reduced the microbial count. Enter the counts before and after treatment to get the log reduction and the percent reduction.
Try sample values — fills the form with the worked example below.
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Log reduction
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Percent reduction (%)
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Fold reduction (×)
Equation: log reduction = log₁₀(N₀) − log₁₀(N) · percent reduction = (1 − 10^( −log reduction)) × 100 · fold reduction = N₀ ÷ N.
Method: Log-reduction calculation for disinfection and thermal-process checks. A 5-log reduction is the target in several food-safety validations, for example FDA juice HACCP (21 CFR 120).
Assumptions: the counts before and after are measured the same way and on the same basis; the reduction is due to the treatment.
Limitations: a zero count after treatment is below the detection limit — the true reduction is at least the value shown, not exactly it; the tool does not test whether the reduction is statistically significant.
Rounding: log reduction and percent to 2 decimal places; fold reduction as a whole number; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Log-reduction calculation for disinfection and thermal-process checks. A 5-log reduction is the target in several food-safety validations, for example FDA juice HACCP (21 CFR 120).
Assumptions: the counts before and after are measured the same way and on the same basis; the reduction is due to the treatment.
Limitations: a zero count after treatment is below the detection limit — the true reduction is at least the value shown, not exactly it; the tool does not test whether the reduction is statistically significant.
Rounding: log reduction and percent to 2 decimal places; fold reduction as a whole number; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Count falls from 1,000,000 to 100. Log reduction = log₁₀(1,000,000) − log₁₀(100) = 6 − 2 = 4.00 log; percent reduction = (1 − 10⁻⁴) × 100 = 99.99%; fold reduction 10,000×.
Enter values above to see results.
A 1-log reduction removes 90%, a 2-log reduction removes 99%, and a 5-log reduction removes 99.999% of organisms. Both counts must be on the same basis (per gram or per millilitre). Tool 048 of 500 — GIFSQ
