GIFSQ Tools · Module 4 — Microbiology Methods & Laboratory Operations · Tool 062 of 500
Plate-count worksheet. Enter the sample, dilution and duplicate plate counts to get the yeast and mold count in CFU per gram.
Try sample values — fills the form with the worked example below.
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CFU/g
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Log₁₀ CFU/g
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Detection limit (CFU/g)
Equation: CFU/g = mean count ÷ (V × d), where d = [sample ÷ (sample + diluent)] × further dilution; V = volume plated (mL); d = total dilution factor. Log₁₀ CFU/g = log₁₀(CFU/g). Detection limit = 1 ÷ (V × d).
Method: Yeast and mold count, ISO 21527-1 and ISO 21527-2. Dichloran rose bengal chloramphenicol (DRBC) agar, 25 °C for 5 days. Countable range 10 to 150 colonies per plate.
Assumptions: Each colony grew from one viable unit; the sample was mixed evenly; the dilution series was prepared correctly; spreading moulds did not overrun the plate.
Limitations: Counts below 10 or above 150 colonies are estimates; fast-spreading moulds can hide yeast colonies; yeasts and moulds are reported together unless counted separately.
Rounding: CFU/g shown as a whole number; log₁₀ to 2 decimal places; intermediates unrounded. In a laboratory report, give CFU/g to 2 significant figures.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Yeast and mold count, ISO 21527-1 and ISO 21527-2. Dichloran rose bengal chloramphenicol (DRBC) agar, 25 °C for 5 days. Countable range 10 to 150 colonies per plate.
Assumptions: Each colony grew from one viable unit; the sample was mixed evenly; the dilution series was prepared correctly; spreading moulds did not overrun the plate.
Limitations: Counts below 10 or above 150 colonies are estimates; fast-spreading moulds can hide yeast colonies; yeasts and moulds are reported together unless counted separately.
Rounding: CFU/g shown as a whole number; log₁₀ to 2 decimal places; intermediates unrounded. In a laboratory report, give CFU/g to 2 significant figures.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: 10 g sample in 90 mL diluent with a further 10⁻³ step, 1 mL plated, duplicate counts 82 and 78. Total dilution = 0.1 × 0.001 = 0.0001; mean count 80; CFU/g = 80 ÷ 0.0001 = 800,000 CFU/g, log₁₀ = 5.90. Both counts are inside the countable range.
Enter values above to see results.
Yeast and mold limits vary widely by product: dried fruit is often specified under 1,000 CFU/g, while fermented foods may carry much higher yeast counts — check the specification for the product. Tool 062 of 500 — GIFSQ
