In fermentation, pH isn't a matter of taste: it's what stops pathogens from growing. Enter your reading, pick your drink, and find out immediately whether to drink it, wait, or bin it.
| Drink | Target range (finished) | Do not exceed |
|---|---|---|
| 🍄 Kombucha | 2.5 – 3.5 | ≤ 4.2 |
| 🍵 Jun | 2.5 – 3.5 | ≤ 4.2 |
| 🫧 Water Kefir | 3.5 – 4.5 | < 4.6 |
| 🥛 Milk Kefir | 4.0 – 4.5 | < 4.6 |
| 🫚 Ginger Beer | not documented | ≤ 4.5 |
| 🌿 Plant Soda | not documented | ≤ 4.5 |
| 🍞 Kvass | not documented | ≤ 4.5 |
The first is 4.6. Below that equilibrium pH, Clostridium botulinum cannot grow: it's the line the FDA uses to define acidified foods (21 CFR 114). Above it, a fermented drink is not safe, however good it smells.
The second is 4.2. That's the value recommended before bottling a fermented drink — a safety margin under the 4.6 line. For kombucha the FDA guidance is explicit: if pH hasn't dropped to 4.2 or below by day 7 of the first ferment, discard the batch (contaminated culture, or fermentation kept too cold).
Between the two, remember 4.5. That's the ceiling we recommend for drinks with no published target range (ginger beer, plant soda, kvass): at 4.5 or below, the botulism risk is ruled out with margin to spare. A limit isn't a target — you don't aim for the exact value at which the danger begins.
Everything else — 'a good kombucha sits at 3.0' — is about taste and maturity, not danger. Useful, but a different conversation.
A ferment that never starts gives you no warning. The liquid looks normal, smells of sweet tea, and yet the pH hasn't moved: the culture is dead, or the room is too cold. Nothing in its appearance will tell you. Only the strip will.
The opposite mistake is just as common: a perfectly safe batch, very acidic, binned out of caution because it 'stings'. A kombucha at 2.6 is vinegar in the making — unpleasant, entirely harmless.
That's why pH is the highest-return measurement in home fermentation: it costs pennies and settles the only question that really matters.
Strips are enough. They tell you which side of 4.6 and 4.2 you're on, and that's all you need to decide. Get a narrow range (2.0-5.0 rather than 1-14), otherwise the reading is too coarse to tell 4.0 from 4.5.
An electronic meter only earns its keep if you want to track the acidification curve day by day, or tune recipes to a tenth of a point. It needs regular calibration — uncalibrated, it lies with great confidence.
One rule for both: measure at room temperature, on a drawn sample. Never dip the instrument into the jar.
Beer, cider, mead, braggot: pH is not a safety threshold there. Alcohol plays that role, with hops in beer. pH governs stability and flavour instead, at different values — which is why this guide shows them no target range rather than inventing one.
Amazake is its own case: koji doesn't acidify. A high pH is normal there, and safety rests entirely on refrigeration and drinking it quickly.
FermPal keeps the thread of your ferments, phase by phase, and reminds you where each one stands. The pH checker is built in, already set to the drink type of the batch you're brewing.
Get started for freepH on target? Move on to the second-ferment sugar calculator for bottling.