GIFSQ Tools · Module 07 — Dairy, Milk, Cheese & Fermented Products · Tool 129 of 500
Follow the pH fall during yogurt fermentation with a first-order model: pH at any time, and the time to reach your target pH.
Try sample values — fills the form with the worked example below.
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pH at chosen time
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Hours to target pH
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Target pH
Equation: pH(t) = final pH + (starting pH − final pH) × e^( −k × t). Time to target pH = −ln((target pH − final pH) ÷ (starting pH − final pH)) ÷ k.
Method: First-order (exponential) model of the pH fall during lactic fermentation; acidity is checked by ISO/TS 11869 titratable acidity and pH by a calibrated meter. The rate constant k is fitted from your own fermentation data.
Assumptions: the pH falls smoothly toward a plateau with a single rate constant; temperature and culture dose stay constant through the run.
Limitations: real fermentations have a lag phase and slow near the end, so the model is a guide, not a prediction — always confirm the set point with a pH reading.
Rounding: pH values to 2 decimal places; times to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: First-order (exponential) model of the pH fall during lactic fermentation; acidity is checked by ISO/TS 11869 titratable acidity and pH by a calibrated meter. The rate constant k is fitted from your own fermentation data.
Assumptions: the pH falls smoothly toward a plateau with a single rate constant; temperature and culture dose stay constant through the run.
Limitations: real fermentations have a lag phase and slow near the end, so the model is a guide, not a prediction — always confirm the set point with a pH reading.
Rounding: pH values to 2 decimal places; times to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Starting pH 6.6, final pH 4.5, k = 0.5 per hour, target pH 4.6. At 4 hours: pH = 4.5 + 2.1 × e^( −2 ) = 4.78; time to pH 4.6 = −ln(0.1 ÷ 2.1) ÷ 0.5 = 6.09 hours.
| Time (hours) | Model pH |
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Enter values above to see results.
Yogurt is usually set at pH 4.6 or below, reached in about 4–6 hours at 40–45 °C. Tool 129 of 500 — GIFSQ
