How to Make Kombucha in a Stainless Fermenter: Step by Step, 5 to 33 Gallons
How to make kombucha in a stainless conical fermenter, from steeping the tea to kegging: ratios by batch size, the temperature for each stage, the cold crash, and carbonating the second ferment in the tank instead of bottles.
In this post
The short answer: steep tea, dissolve sugar in it, cool it below 85°F, add starter liquid from a previous batch and a SCOBY, and let it ferment open to the air at 75 to 80°F for 7 to 14 days. For fizz, seal it with a little fruit juice or sugar for a second ferment of 2 to 5 days, then chill it to 34 to 38°F to stop the fermentation before you keg or bottle.
That works in a gallon jar on the counter. Past a couple of gallons the jar stops making sense, and a stainless conical fermenter takes over: the tea steeps in the tank, the tank holds temperature, you taste from a valve instead of dipping a cup, yeast drops out of the cone, and a pressure-rated tank carbonates the second ferment with no bottles at all. Here is the whole process for 5 to 33 gallon batches.
What you need
- A stainless fermenter. 304 or 316 stainless. Kombucha finishes around pH 2.5 to 3.5, more acidic than beer, which rules out aluminum, plastic that scratches, and anything with brass or lead solder in contact with the liquid. Tri-clamp fittings and silicone gaskets have nothing the acid can attack.
- A way to heat water and steep tea. A kettle works, or a heating element in the fermenter itself, with a stainless tea basket hanging in the top opening.
- Starter liquid and a SCOBY from a healthy previous batch.
- Plain black or green tea and white sugar. Avoid flavoured teas with oils; the oils can harm the culture.
- Filtered water. Chlorine boils off, but chloramine does not, and both slow the culture. A carbon filter removes both.
- For carbonation: a pressure-rated tank with a spunding valve, or bottles.
- For selling: a way to chill the tank to 34 to 38°F, and a pH meter.
Ratios by batch size
Per gallon of finished kombucha: about 1 cup (200 g) of sugar, 8 to 10 g of loose tea (four to five tea bags), and at least 10% of the batch as starter liquid from the previous batch. More starter is safer: it drops the pH fast, which is what keeps mould and other organisms out.
| Tank | Max batch | Sugar | Tea | Starter (10–15%) |
|---|---|---|---|---|
| 8 gal | 6.5 gal (25 L) | 1.3 kg | 60 g | 2.5 to 3.5 L |
| 13 gal | 11 gal (42 L) | 2.2 kg | 100 g | 4 to 6 L |
| 26 gal | 22 gal (83 L) | 4.4 kg | 200 g | 8 to 12 L |
| 1 BBL | 33 gal (125 L) | 6.6 kg | 300 g | 12.5 to 19 L |
Kombucha doesn't foam like beer, so it needs much less headspace: fill to about where the straight wall meets the top dome. Above that the surface narrows, and the SCOBY needs the full surface. Leave room to work at the top without disturbing it.
Other batch sizes or your own recipe: the kombucha calculator works out the tea, sugar, starter and water, plus the second-ferment sugar, carbonation pressure and alcohol. Or start from one of our kombucha recipes.
Temperatures at a glance
| Stage | Temperature | Time |
|---|---|---|
| Steep the tea | 190–200°F (black) · 175°F (green) | 10–15 minutes |
| Add the culture | below 85°F | — |
| First ferment | 75–80°F | 7–14 days |
| Second ferment | 72–78°F | 2–5 days |
| Cold crash | 34–38°F | 1–2 days, then keep cold |
Kombucha is a warm fermentation. Most of the time you are holding the tank warm, not cooling it; the only cold step is the crash at the end.
Step by step
1. Heat the water and steep the tea
If you steep in the fermenter, fill it to the full batch volume first. A tea basket hangs from the top opening and reaches down into the tank, so the water has to be high enough to cover the tea in the bottom of the basket; a half-full tank leaves it hanging in the air. Heat the water to steeping temperature with the tank's element, steep loose tea in the basket for 10 to 15 minutes, then lift the basket out by its handle. No kettle to lift, no transfer, and the basket keeps the leaves out of the batch.
Steeping in a kettle instead? Then you can steep in part of the water and top up with cold water later (see step 3).
2. Dissolve the sugar
Stir the sugar into the hot tea until it is fully dissolved. Hot tea dissolves it in a minute; cold tea takes much longer.
3. Cool below 85°F
Two ways:
- Chill the full batch. If you steeped the whole batch in the tank, pump it through a counterflow chiller and back into the tank until it reads below 85°F. With no chiller, seal the tank and let it cool overnight; it is slow, but it works.
- Concentrate and top up. If you steeped in a kettle, use a third to a half of the batch water, then top up with cold, filtered water in the fermenter. It needs no extra equipment. Check the temperature before going on; on a warm day you may need to wait.
Never add the culture to hot tea. Above about 90°F it starts to suffer, and much hotter kills it.
4. Add the starter and the SCOBY
Pour in the starter liquid, then lay the SCOBY on top. Check the pH if you have a meter: it should be below 4.6 right away, and most brewers aim for 4.2 or lower. If it is higher, add more starter.
5. First ferment: warm and open to the air
This is where kombucha differs most from beer. The acetic acid bacteria that give kombucha its tang need oxygen at the surface, which is why the SCOBY forms a mat on top. So:
- No airlock and no pressure. Cover the top opening with a tightly woven cloth to keep fruit flies out and let air in.
- Hold 75 to 80°F. Cooler and it stalls; warmer and it turns vinegary fast. In a cold room, a heating element on a controller holds the temperature: it only pulses at a low setting, which the culture never feels. Only hold temperature with a full batch, so the element stays covered.
- Keep it out of direct sun and away from fermenting beer.
Taste from the sample valve daily from day five. You want a balance of sweet and tart, usually at pH 3.0 to 3.5, in 7 to 14 days. Sampling from the valve rather than dipping a cup is the big advantage over a jar: the SCOBY is never disturbed.
6. Drop the yeast and save the starter
Kombucha throws brown yeast strands and sediment that settle in the cone. Open the bottom valve for a second into a bucket and dump them. What stays is clearer, and the second ferment carbonates more predictably.
Keep a jar of the finished first-ferment liquid as the starter for the next batch, and lift the SCOBY out into it with clean hands or a sanitized tray.
7. Second ferment: flavour and carbonate in the tank
The traditional second ferment is bottles: fruit, sugar, cap, wait, and hope none of them explode. In a pressure-rated fermenter you do it in the tank:
- Add fruit purée, juice or a little sugar through the top (about 1 to 2 cups of juice per gallon).
- Seal the lid and fit a spunding valve set to 10 to 12 psi.
- Hold 72 to 78°F for 2 to 5 days. The remaining yeast ferments the new sugar, and the CO₂ stays in solution instead of venting. Taste from the sample valve.
Want a set carbonation level, faster? Skip the extra sugar and force-carbonate cold through a carbonation stone instead.
8. Cold crash
Chill the tank to 34 to 38°F for a day or two. The crash stops the yeast, so the sweetness, the acidity and the alcohol stop changing; it drops the remaining sediment; and cold kombucha holds its carbonation. Without a crash, kombucha keeps fermenting in the keg or the bottle.
The crash needs real cooling: glycol through the fermenter jacket. Tap water can't get the tank that cold. For home batches, kegging warm and putting the keg straight in the fridge does the same job more slowly.
9. Keg or bottle
Draw the clear kombucha off above the sediment with a racking arm and push it into kegs with a closed transfer kit. Serve from a tap, or fill bottles that are already carbonated and cold. Keep finished kombucha refrigerated.
Alcohol: what sellers need to know
Kombucha always makes a little alcohol, and it can climb past 0.5% ABV, especially in a warm second ferment or if it keeps fermenting after packaging. In the US, a drink at 0.5% ABV or more is regulated as an alcoholic beverage, so commercial producers test every batch and crash and refrigerate to keep it below that. If you sell, check your local food and licensing rules before your first batch.
Cleaning between batches
Rinse, recirculate hot alkaline cleaner through a CIP spray ball for twenty minutes, rinse, and sanitize. Pull the valves and gaskets and soak them; SCOBY fragments hide in gaskets, so inspect them, and replace silicone tri-clamp gaskets when they look tired.
One rule if the tank also makes beer: the acetic acid bacteria in a SCOBY are exactly the bacteria beer brewers fear. Either dedicate the tank to kombucha, or run a full hot caustic clean, sanitize, and replace the gaskets before it sees beer again, and keep separate hoses and sample valves for the two.
Troubleshooting
| Problem | Cause | Fix |
|---|---|---|
| Vinegar in five days | Too warm, or too much starter | Hold 75°F; use 10–15% starter, not more |
| Still sweet after ten days, no new SCOBY | Too cold, or the culture went into hot tea | Warm the tank to 78–80°F; restart with fresh starter if nothing changes |
| Fuzzy, dry, coloured spots on the SCOBY | Mould: not enough acid at the start | Discard the batch and the SCOBY; use more starter next time |
| Flat second ferment | Not enough sugar, or all the yeast dumped | Add 1 cup juice or 2 tbsp sugar per gallon; dump less aggressively |
| Over-carbonated | Spunding valve set too high, or too long warm | Set 8 to 10 psi; crash sooner |
| Keeps getting sourer in the keg | Never crashed | Crash to 34–38°F before kegging and keep it cold |
Frequently asked questions
How long does kombucha take to make?
About two to three weeks from tea to keg: 7 to 14 days for the first ferment, 2 to 5 days for the second, and a day or two to crash.
What temperature should kombucha ferment at?
75 to 80°F for the first ferment and 72 to 78°F for the second. Below about 70°F it slows down a lot and is more prone to mould; above about 85°F it sours fast.
Can you make kombucha in a conical fermenter?
Yes. A stainless conical makes larger batches easier: you steep and ferment in one vessel, taste from a valve, dump yeast from the cone, and, if it is pressure-rated, carbonate the second ferment in the tank. The only change from beer is that the first ferment runs open to the air.
Does kombucha need oxygen?
Yes, during the first ferment. The acetic acid bacteria need air at the surface. That is why the first ferment runs under a cloth, not an airlock, and the second ferment, which is about carbonation, runs sealed.
How do I know if it's mould or a new SCOBY?
New SCOBY is smooth, pale and wet, and often has brown yeast strands hanging from it. Mould is fuzzy, dry and sits on top in round spots, usually white, green or black. If you see mould, throw out the batch and the SCOBY.
The setup
Our Kombucha Brewing System puts all of this in one jacketed stainless Unitank: a stainless tea basket that hangs in the top opening, a heating element and controller to steep and then hold fermentation temperature, a pump and tubing set, a counterflow chiller to chill the batch in one pass, a racking arm and a transfer kit. It comes in 8, 13 and 26 gallon tanks and 1 BBL, making up to 6.5, 11, 22 and 33 gallons a batch. Add the Kombucha Pro Kit to carbonate in the tank and clean in place, and a glycol chiller for the cold crash a kombucha business needs. Ask us if you are planning a kombucha cellar.