Bottling & carbonation
A keg replaces your bottles, not your brewing jar. Four parts, and the cheapest of them costs less than a bag of tea.
By Scooter M.·Published September 14, 2026
The short answer
A keg is not a brewing vessel. It replaces your bottles — the cold, carbonated, finished end of the process — and the first fermentation still happens in an open-topped jar under a cloth. If all you want is reliable fizz, a ten-dollar carbonation cap and a cartridge regulator get you there without a keg at all. Buy a keg when washing bottles has become the reason you brew less often.
This is the part most kegging pages skip, and it is the part that decides whether you are about to waste a hundred and fifty dollars.
The first fermentation is aerobic. The culture needs air exchange, which is why every brewing jar on this site takes a cloth and a band rather than a lid, and why sealing that stage is the one thing you must not do. A keg is a sealed pressure vessel. It cannot host a first fermentation and nothing you buy on this page changes that. Your brewing vessel stays exactly where it is.
What a keg replaces is the seven swing-top bottles a gallon fills. Instead of distributing the finished drink into glass and waiting days for a second fermentation to build pressure, you move the whole batch into one vessel, push CO2 into it, and pour from it. The carbonation stops being a fermentation you wait out and becomes a dial you set.
That swap buys three things. Washing one keg instead of seven bottles. Carbonation you choose rather than guess at, which is the entire subject of why kombucha does not carbonate. And cold storage that stops the ferment dead, because a keg in a refrigerator is a batch that stops getting more sour on Thursday.
It costs you cupboard space, a gas supply, and the acceptance that your kitchen now contains a pressure vessel.
Kegging gear is sold to beer brewers, and beer brewers make five gallons at a time of something that is finished fermenting when it goes in. Neither of those is true here, which changes what matters.
A working setup is a vessel, a gas source, a way to connect them and a way to pour. You can skip the vessel entirely, which is the route most people should try first.
| Part | What it does | Can you skip it? |
|---|---|---|
| Keg | Holds the batch sealed and under pressure, and dispenses from a dip tube | Yes — a carbonation cap puts a PET bottle in its place |
| CO2 source | Supplies the gas. A cartridge regulator or a refillable cylinder | No. Force carbonation is the whole point |
| Disconnects | Ball lock fittings that clip onto the gas and liquid posts | Sometimes — some kegs and regulators ship with them |
| Line and tap | Carries the drink from the liquid post to a glass | Only if you are carbonating in bottles rather than a keg |
Ball lock is the fitting standard worth committing to. Gas posts and liquid posts are different sizes so they cannot be crossed, the disconnects clip on by hand, and everything on this page speaks it. The alternative standard, pin lock, is older and harder to buy parts for.
The cap is the cheap experiment. The two kegs are the commitment, and which one depends entirely on whether you brew in batches or run a continuous brew.
FERRODAY
A stainless ball-lock cap that turns an ordinary soda PET bottle into something you can push CO2 into, which is the cheapest honest way to decide your own fizz.
#ad Price as of October 18, 2026. How this is funded.
MRbrew
The only keg here sized for the batch this site's readers actually brew, in a named 304 stainless, with both disconnects and a full gasket set already in the box.
#ad Price as of October 18, 2026. How this is funded.
TMCRAFT
Fourteen and a half inches tall with a published 130 psi ceiling and a pull-ring relief valve on the lid — the only keg here that fits a fridge shelf and the only one that can vent itself.
#ad Price as of October 18, 2026. How this is funded.
Two sizes are worth considering for kombucha and the five-gallon default is not one of them. Here is what each maker actually publishes.
| Keg | Capacity | Steel grade stated | Pressure stated | Height | Relief valve |
|---|---|---|---|---|---|
| MRbrew ball lock | 1.6 gal / 6 L | Food-grade 304 | 80-90 psi “safety value” | Not published | Not stated |
| TMCRAFT ball lock | 2.5 gal | Not named | Up to 130 psi | 14.5 in | Pull-ring on the lid |
| Typical 5 gal corny | 5 gal | Varies by maker | Varies by maker | About 24 in | Varies by maker |
The two candidates trade exactly the things you would want them not to. MRbrew names its grade — food-grade 304, which is the answer this site wants — and then publishes no dimensions, no weight and no relief valve. TMCRAFT publishes a pressure ceiling, a height you can measure against a fridge shelf and a pull-ring relief valve on the lid, and then describes its steel only as "fully passivated". Passivation is a surface treatment. It is not a composition, and it does not tell you what alloy is underneath.
Neither omission is disqualifying and both are worth knowing before you order. If the keg will live in a refrigerator and hold a live drink, the relief valve and the published height are worth more. If it will hold a finished, refrigerated batch and you want the alloy named, the 1.6 gallon is the one.
On size: a 1.6 gallon keg takes a standard one-gallon batch with genuine headspace and nothing wasted. A 2.5 gallon keg suits someone drawing off a continuous brew a couple of gallons at a time. The five-gallon keg that dominates this category is sized for a beer batch and is the wrong purchase for almost everyone reading this.
This is where beer guidance will mislead you, because the numbers are not the same and the reason is temperature.
Forced carbonation works by holding a liquid under CO2 until the gas dissolves into it, and how much dissolves depends on pressure and on how cold the liquid is. Cold liquid absorbs far more gas at the same pressure. A refrigerated keg therefore needs modest pressure; a keg at room temperature needs much more to reach the same fizz, which is the practical argument for refrigerating before you carbonate rather than after.
The specific numbers depend on how fizzy you want it and how cold your fridge runs, and this page is not going to publish a table of psi values as though they were a standard. What is worth stating plainly is the shape: a 0-60 psi regulator has far more range than kombucha will ever use, and the risk in this hobby is not that your regulator cannot reach high enough.
The kombucha-specific complication is that the drink is not finished. Beer goes into a keg fermented out. Kombucha goes in alive, with residual sugar and an active culture, and it will keep producing CO2 of its own accord unless it is cold. That is a second pressure source you did not set on the dial, and it is the reason a relief valve on the lid is worth paying attention to.
There are two honest routes to CO2 and the right one depends on how often you will do this, not on how serious you are.
A mini regulator threads onto a disposable CO2 cartridge, reads out on a small dial and fits in a drawer. It is the low-commitment route and it is genuinely sufficient: the FERRODAY unit here publishes a 0-60 psi range, takes 3/8 in threaded cartridges and ships with a ball lock gas disconnect, so it works with either a keg or a carbonation cap the day it arrives. What it does not publish — and this is a real gap — is how much carbonating one cartridge does. Nobody in this category publishes that figure, which means the running cost is something you discover rather than something you can plan.
The other route is a refillable aluminum cylinder with a CGA-320 valve and a full-size regulator. Cylinders ship empty, need filling at a welding-gas or homebrew supplier, and cost several times what a mini regulator does before they have delivered a single bubble. Per ounce of gas they are dramatically cheaper, and the crossover comes quickly if you keg regularly. They also take floor space and have to be driven somewhere.
For a kombucha brewer carbonating a gallon every week or two, the cartridge route is the sane starting point. Buy the cylinder when you have annoyed yourself buying cartridges.
A sealed keg pours nothing until there is a liquid disconnect, a line and a tap on the other end of it. A picnic tap assembly is the cheap version of all three: a squeeze faucet on a few feet of tubing with the ball lock disconnect already fitted.
Two things about it are worth knowing in advance. The first is foam. How fast a carbonated drink can move down a line without breaking out of solution depends on the length and the internal bore of that line, and three feet is short. Most makers, including this one, publish neither the bore nor the tubing polymer, so balancing a pour is trial and error rather than arithmetic. If pours foam, a longer line is the usual fix.
The second is sediment. A corny keg draws from a dip tube that reaches the bottom of the vessel, and the bottom of the vessel is exactly where kombucha yeast settles. The first pour off a freshly filled keg is often cloudy for that reason. It is cosmetic, not a fault, and it clears. Straining at transfer with a fine mesh strainer reduces it.
Most people reading this do not need a keg. They need carbonation they can rely on, and there is a ten-dollar answer to that.
A carbonation cap is a ball lock post on a threaded cap that screws onto an ordinary soda PET bottle. Fill the bottle, cap it, clip the gas disconnect on, apply pressure, shake, leave it cold. You get the same forced carbonation a keg gives you, on one bottle at a time, using the same regulator you would have bought anyway. The cap and the regulator together cost a fraction of the cheapest keg here.
The honest limits: it carbonates one bottle at a time, that bottle is plastic rather than the swing tops you probably already own, and the maker publishes no pressure rating on the cap and no thread standard beyond "most soft drink PET bottles". For finding out whether force carbonation is something you actually want, none of that matters much.
Whichever route you take, there has to be a gas source. The tap is only needed once there is a keg to pour from.
FERRODAY
A cartridge regulator with a 0-60 psi dial and a gas disconnect already in the box — every pressure kombucha needs, in something that lives in a drawer.
#ad Price as of October 18, 2026. How this is funded.
FERRODAY
Two pre-assembled tap-and-line sets with the liquid disconnects already fitted, which is the cheapest way to turn a sealed keg into something you can pour from.
#ad Price as of October 18, 2026. How this is funded.
In relative terms, because the live figures are on the buy rows above and they move.
The carbonation-cap route — one cap plus a cartridge regulator — lands in the same bracket as a decent set of swing-top bottles, and less than a mid-range brewing kit. It is a genuinely small purchase.
A keg setup is roughly four to six times that: the keg is the largest line item by a wide margin, with the regulator and a tap assembly adding meaningfully on top. A keg costs more than most one-gallon brewing jars and more than most starter kits. Nothing about it makes better kombucha. It makes the finishing end of the process faster and more repeatable, which for some people is the difference between brewing monthly and brewing weekly, and for others is a stainless cylinder in the cupboard.
Cartridges are a running cost with no published figure behind it. A refillable cylinder moves that cost down and moves the up-front cost up. If you cannot tell which side of that you are on yet, you are on the cartridge side.
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Ranked on the published rubric. Every row jumps to that product's full write-up below; the button goes straight to Amazon.
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 | FERRODAY Stainless Steel Carbonation Cap, 5/16 in Barb A stainless ball-lock cap that turns an ordinary soda PET bottle into something you can push CO2 into, which is the cheapest honest way to decide your own fizz. | Carbonating without buying a keg | 7.4out of 10 | |
| 2 | MRbrew 1.6 Gallon Ball Lock Keg (Cornelius) The only keg here sized for the batch this site's readers actually brew, in a named 304 stainless, with both disconnects and a full gasket set already in the box. | A one-gallon batch, kegged | 8.4out of 10 | |
| 3 | TMCRAFT 2.5 Gallon Ball Lock Keg with Rubber Handles Fourteen and a half inches tall with a published 130 psi ceiling and a pull-ring relief valve on the lid — the only keg here that fits a fridge shelf and the only one that can vent itself. | Continuous brew, and a keg that fits a refrigerator | 7.9out of 10 | |
| 4 | FERRODAY 0-60 PSI Mini Keg Regulator, CO2 Cartridge A cartridge regulator with a 0-60 psi dial and a gas disconnect already in the box — every pressure kombucha needs, in something that lives in a drawer. | The gas side without a cylinder | 7.2out of 10 | |
| 5 | FERRODAY 3 ft Ball Lock Beer Line Assembly with Picnic Tap Two pre-assembled tap-and-line sets with the liquid disconnects already fitted, which is the cheapest way to turn a sealed keg into something you can pour from. | Getting the drink back out of the keg | 6.7out of 10 |
#1 · Carbonating without buying a keg
A stainless ball-lock cap that turns an ordinary soda PET bottle into something you can push CO2 into, which is the cheapest honest way to decide your own fizz.
Who it is for. Anyone whose second ferment keeps coming out flat, and anyone who wants the carbonation level decided on purpose.
Source: FERRODAY published Stainless Steel Carbonation Cap listing (high quality stainless steel construction, ball lock fitting with 5/16 in barb, ideal for forced carbonation in PET bottles, food-safe rubber gaskets with two spare O-rings and one spare gasket added to the package, about 3.6 oz), Amazon B01K4GGYT0, retrieved 2026-09-14
Skip it if. Your second ferment already carbonates reliably in swing tops. This solves a problem you do not have.
#ad Price as of October 18, 2026. How this is funded.
#2 · A one-gallon batch, kegged
The only keg here sized for the batch this site's readers actually brew, in a named 304 stainless, with both disconnects and a full gasket set already in the box.
Who it is for. A one-gallon brewer tired of washing seven bottles, who wants the whole batch cold, carbonated and on tap in a single vessel.
Source: MRbrew published 1.6 Gallon Ball Lock Keg listing (food-grade 304 stainless steel, 1.6 gallon / 6 L capacity, recommended safety value 80-90 PSI, dual 19/32 in-18 threaded ball lock posts, two included ball lock fittings for gas and liquid, 8-piece silicone gasket set with removal tool), Amazon B0F7XQRNDF, retrieved 2026-09-14
Skip it if. You brew a gallon a fortnight and drink it out of swing tops happily. A keg is a dispensing convenience, not a brewing upgrade.
#ad Price as of October 18, 2026. How this is funded.
#3 · Continuous brew, and a keg that fits a refrigerator
Fourteen and a half inches tall with a published 130 psi ceiling and a pull-ring relief valve on the lid — the only keg here that fits a fridge shelf and the only one that can vent itself.
Who it is for. A continuous-brew brewer drawing off a couple of gallons at a time who would rather have it sealed, cold and carbonated than standing in bottles.
Source: TMCRAFT published 2.5 Gallon Ball Lock Keg listing (fully passivated stainless steel construction, stainless lid with pull-ring style pressure release valve, designed to food-safe NSF and ISO 9001 standards, withstands pressure up to 130psi, double ball lock post design, stated 8.3 x 8.3 x 14.4 in against catalog dimensions of 9 x 8.5 x 14.5 in, one year warranty), Amazon B0C1NB6F3J, retrieved 2026-09-14
Skip it if. You brew one gallon at a time. Two and a half gallons of keg for one gallon of kombucha is a lot of headspace to fill with CO2.
#ad Price as of October 18, 2026. How this is funded.
#4 · The gas side without a cylinder
A cartridge regulator with a 0-60 psi dial and a gas disconnect already in the box — every pressure kombucha needs, in something that lives in a drawer.
Who it is for. Anyone carbonating a bottle or a small keg occasionally, who wants the gas to live in a drawer rather than on the kitchen floor.
Source: FERRODAY published 0-60 PSI Mini Keg Regulator listing (0-60 psi dial display, knob adjustment stated in place of a trigger valve, fits 3/8 in threaded CO2 cartridges with cartridges not included, ships with a 3/8 in adapter and one ball lock gas disconnect, anodized aluminum body with a refined copper cartridge base), Amazon B0B4B4J76D, retrieved 2026-09-14
Skip it if. You expect to keg every week. Buy a CGA-320 cylinder and a full-size regulator instead and stop paying per cartridge.
#ad Price as of October 18, 2026. How this is funded.
#5 · Getting the drink back out of the keg
Two pre-assembled tap-and-line sets with the liquid disconnects already fitted, which is the cheapest way to turn a sealed keg into something you can pour from.
Who it is for. Anyone who has just bought a keg and currently has no way of getting the drink back out of it.
Source: FERRODAY published 3 ft Ball Lock Beer Line Assembly listing (2 picnic taps, 2 x 3 ft clear food-safe lines, 2 ball lock disconnects, 2 swivel nuts and 4 hose clamps, all pre-assembled, ABS ball lock disconnects with stainless steel swivel nuts and clamps, 11.8 x 7.8 x 2.3 in package), Amazon B07VVNRZHM, retrieved 2026-09-14
Skip it if. Your keg already came with liquid disconnects and you own food-grade tubing. This set is convenience, not capability.
#ad Price as of October 18, 2026. How this is funded.
Every specification cited on this page came from one of these documents, retrieved on the date shown against the product it belongs to.
Bottles compared on published pressure ratings, closure type, glass color and size — and which bottles must never hold a second ferment.
Which bottles are built for pressure, which only look like it, and how to run a second ferment without cleaning kombucha off a ceiling.
The five causes of a flat second ferment, ranked by how often each is actually the problem — starting with the one nobody checks.
Three continuous brew vessels compared on published capacity, height with stand and spigot material — plus the tapless option.
Reserve the starter, strain, fill with headroom, seal and condition — with the quantities and the two things people get wrong.
Which swing tops publish a pressure rating, which are storage bottles wearing the same shape, and how to tell them apart before you fill them.