Current status
— estimated pH
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Estimated time to bottling
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What this means
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Estimates use a rate of change of roughly −0.010 pH units per day at 20 °C, adjusted with a Q10-style factor of about 1.6 for every 10 °C change — a widely used approximation, not a measurement of your brew. Always confirm with strips or a calibrated meter before bottling, and treat pH 3.5 as a threshold to approach, not a target to hit exactly.
Why pH is the measurement that matters
Acidity is safety, not taste
A falling pH is what makes the environment hostile to unwanted microbes. Taste tells you how the brew is progressing; pH tells you whether it is safe to bottle.
Temperature sets the pace
Warmer ferments acidify faster and can overshoot into vinegar. Cooler ferments are slower and gentler. Steady beats fast almost every time.
The 3.5 threshold
pH 3.5 or below is the figure most home-brewing guidance uses as the point at which bottling is considered safe. Below 3.0 the brew is very sharp and better kept as starter.
Estimates are not readings
Culture health, vessel geometry, sugar type and starter proportion all move the rate. Use this estimator to plan, then measure to decide.
Reading the pH scale
| pH reading | What it usually means | What to do |
|---|---|---|
| Above 4.6 | Barely acidified — often the first day or two | Keep it warm, covered and undisturbed |
| 4.0 – 4.6 | Actively fermenting | Taste daily, do not bottle yet |
| 3.5 – 4.0 | Approaching the bottling threshold | Start tasting; prepare bottles |
| 3.0 – 3.5 | Ready to bottle under standard guidance | Bottle, keep back starter, refrigerate once carbonated |
| Below 3.0 | Very acidic | Use as starter for the next batch or dilute |
If a reading looks wrong, check the measurement before changing the brew. Uncalibrated meters, strips read under the wrong light, and samples taken through a pellicle all give misleading numbers. Re-test with a clean sample before drawing conclusions.
About these calculators
The formulas behind these tools are widely published home-brewing approximations, not laboratory-grade models. They are intended to point you in the right direction and to make your own batches repeatable — they are not a substitute for measuring your brew, and they cannot guarantee a result.
- Every calculator runs entirely in your browser. Nothing you type is transmitted, logged or stored.
- Figures are approximate. Tea strength, sugar type, room temperature, vessel shape and the health of your culture all shift the outcome.
- pH is a safety-relevant measurement. Treat the estimator as a planning aid only, and confirm with strips or a calibrated meter before bottling.
- Finished kombucha contains trace alcohol and caffeine. It is not suitable for children, and anyone who is pregnant, breastfeeding, immunocompromised, diabetic or taking medication should consult a healthcare professional before drinking it.
- Kombucha is a food, not a medicine. Nothing on this site claims it treats, cures or prevents any disease.