Free tool · no sign-up
Kombucha tuner
Tell us what you want and how warm your kitchen is. We'll give you your amounts and the days it comes into its prime.
How you want it
Adjust the proposal
More profiles
Fizz
Here you adjust the proposal from above; the four axes — intensity, balance, fizz and complexity — are the mentor's fine controls and they live in the app. What the four axes are · Formulate with the four axes
Your proposal, for 3 litros
See the numbers
This window assumes a steady 22 °C. Your kitchen isn't steady.
Thanks — that genuinely helps
The model improves with real fermentations, not with theory. If you like, we'll email you on the day this calculation says your kombucha comes into its window, and you tell us how it went.
One email only, if that's all you tick. One click to unsubscribe, always. Privacy
Done — we've sent you the proposal. Check your inbox.
You're going fast
With a free account you keep them all, sorted by ferment — and the mentor turns any of these calculations into a batch it walks with you.
Create a free accountThat's two calculations. Shall we ferment them together?
A calculation is the beginning. With a free account it becomes a batch: the mentor walks the days with you, tells you when the window opens and keeps how it turned out — which is what makes the next one surer. Three minutes and the first one is under way.
Free, 2 active batches, no card.
How much sugar per litre of kombucha
The usual reference is around 70 g per litre, but the number on its own means nothing: part of that sugar ends up in the glass and part gets eaten by the microbes to make the fizz. If you're bottling with bubbles, what leaves as carbon dioxide has to be replaced. That's why the tuner splits the sugar in two rather than handing you a single figure.
How long does kombucha take to ferment
Mostly it depends on temperature. Every 10 °C warmer doubles the speed: what takes ten days at 18 °C can be there in six at 28 °C. That's why a recipe saying «14 days» is right in one kitchen and wrong in the one next door. The honest answer is a window, and a window that moves when conditions do.
Why never less than five days
Even when the numbers come out sooner, kombucha doesn't speed up below five days. It isn't a matter of speed but of order: the yeasts work first, the acetic bacteria after. Skipping that order doesn't give you fast kombucha, it gives you sweet tea with alcohol in it.
How much starter liquid
Between 8 and 20 % of the volume. More starter is faster and protects against contamination, but it leaves less room for aromas to develop: the kombucha comes out flatter. Less starter gives more complexity and more risk.
The second ferment and the fizz
What matters here is the sugar left at bottling plus whatever the fruit brings. And there's an uncomfortable consequence: the fizz and the alcohol come from the same sugar, so they rise together. That's why the tuner tells you the estimated pressure and how many days are left before the risk zone, not just how many bubbles you'll get.
If it comes out too sour
Almost always it was cut late, and almost always because it was warmer than anyone thought. This is the case that keeping records fixes best: once you know what temperature it really sat at and which day you cut it, adjusting the next one stops being guesswork. The full kombucha guide goes into detail.
Frequently asked
Do I need to sign up?
No. The tuner is free and doesn't ask for your email. An account is for something else: turning the calculation into a batch the mentor walks with you.
Where do the numbers come from?
From a model anchored in real fermentations measured over years, not from copied recipes. It returns ranges, not certainties, and it's built so a single data point can correct it.
Does it work for any kombucha?
It's built for tea-and-sugar kombucha, between 1 and 12 litres, and between 16 and 30 °C. Outside that it will tell you, instead of making a number up.
Does it work for Jun or honey kombucha?
You can pick honey as the sugar and the calculation adjusts, but Jun has its own culture and its own rhythm. It's a candidate for a tuner of its own.
What about the other ferments?
The kombucha tuner is the first one. For sauerkraut and pickles there's the brine calculator, and the rest lives inside the app.
What are the four axes?
They're the four decisions that describe the kombucha you want, before anyone talks grams. Intensity: how much body and how much sweetness to start from. Balance: which way the result leans, from sweet to sour. Fizz: how many bubbles you want in the bottle. And complexity: whether you're after something clean and direct or something with more depth and layers. Every preset in the tuner is one concrete, already-tested combination of the four: when you pick «balanced» or «strong» you're not picking a name, you're setting those four values at once. We deliberately don't show them loose here — a phrase decides just as well, without having to understand the scale. Moving them one by one is what the app's formulator does.
The pressure and alcohol figures are estimates. The risk threshold depends a great deal on the bottle you use: a swing-top soda bottle doesn't take what a champagne bottle takes. When in doubt, chill it early and release the gas daily.
The calculated alcohol is indicative. If you're going to sell what you ferment, European rules set 0.5 % and 1.2 % as the relevant thresholds and it has to be measured, not estimated.