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Bottling from a keg: beer guns and counter-pressure fillers

Bottling from a keg with a beer gun or counter-pressure filler: chilling, CO2 purge, fill pressure, capping on foam, plus nitro basics and safety limits.

Updated November 2026 · 7 min read

A glass being filled from a row of chrome beer taps
Photo: Connor Ki, CC BY-SA 4.0, via Wikimedia Commons
The short version
  • Bottling from a keg lets you take carbonated, clear beer to a club meeting or competition without priming or yeast sediment.
  • Counter-pressure fillers purge the bottle with CO2 and fill it under pressure; beer guns are simpler and fill at low pressure into a CO2-purged bottle.
  • Cold beer foams less: chill the keg as cold as practical, and BYO suggests raising pressure 2–3 psi overnight to offset carbonation loss.
  • BYO’s method fills at roughly the keg’s conditioning pressure (often 8–12 psi) in about 5–10 seconds per bottle, then caps on foam.
  • Keg-filled bottles are ready to serve, but they are not primed, so they stay at the keg’s carbonation level.

Bottling from a keg solves a problem every kegger runs into: how to share beer that lives in a corny keg. Competitions want bottles, friends want a six-pack, and a growler goes flat within days. Filling bottles from the keg keeps the carbonation and clarity you already have, with no priming sugar and no yeast layer.

This guide compares the main tools (beer guns, counter-pressure fillers, multi-head fillers and automated fillers) from maker listings and BYO’s counter-pressure technique articles, then walks through the steps. Nitro beer gets a short section at the end. We did not fill bottles with these products; follow each maker’s instructions.

Beer gun vs counter-pressure filler

A counter-pressure filler seals onto the bottle, fills it with CO2 to the same pressure as the keg, then lets beer flow in as you slowly bleed off the gas. Because the pressures balance, the beer barely foams and keeps its carbonation. A beer gun purges the bottle with CO2 and fills from the bottom at low pressure without sealing the bottle; it is simpler and faster to clean, and BYO-cited sources note it does not control headspace pressure the same way.

Ball-lock corny kegs and a larger keg stacked on a pallet
Both fillers start from a cold, carbonated corny keg.Photo: Czeva, CC BY-SA 4.0, via Wikimedia Commons

Ways to bottle from a keg

MethodHow it worksBest forTrade-offs
Counter-pressure fillerSeals the bottle, purges and pressurizes it, beer flows in as gas bleeds offCompetition bottles, highly carbonated styles~ More valves to learn and clean
Beer gunCO2 purge, then bottom fill at low pressure, unsealedBatches of a dozen or more, quick sessions~ Some carbonation loss; needs very cold beer
Faucet-mounted fillerSlides into a forward-sealing faucetKegerators with forward-sealing faucets~ Faucet must be compatible
Multi-head or automated fillerSeveral heads or a programmed pinch valveLarge runs, cans~ More parts, more setup, may need 110–120V power
Tube from a picnic tapBottom fill with no purgeSame-day drinking only✗ Oxygen pickup and foam

Source: BYO: Counter-pressure bottling techniques; maker listings

Bottling from a keg, step by step

  1. Carbonate fully and chill hard

    The keg should be fully carbonated and as cold as practical; cold beer holds CO2 and foams less. BYO notes some brewers raise CO2 pressure 2–3 psi overnight to offset the loss during transfer.

  2. Chill and sanitize the bottles

    Cold, sanitized bottles reduce foaming. Use a no-rinse sanitizer at label dilution and let it drain.

    Five Star Star San Acid Sanitizer, 32 ozFastRack Bottle Rinser (Sulphiter)
  3. Set up with valves closed

    Close every valve on the filler and turn off the gas before connecting. Gravity-type fillers need the keg higher than the bottles.

  4. Purge with CO2

    Fill each bottle with CO2 first to push out air. Oxygen is what makes bottled beer taste stale weeks later.

  5. Fill under pressure

    BYO’s guidance is roughly the keg’s conditioning pressure, often 8–12 psi, filling from the bottom under the CO2 blanket in about 5–10 seconds with only a little foam.

  6. Cap on foam

    Cap right away. Capping over a little foam pushes out the last air; a light tap on the bottle can raise foam. Oxygen-absorbing caps add margin.

    Ferrari Super Agata Bench CapperFastRack Oxygen Absorbing Crown Caps, 26 mm, 144 Ct
  7. Clean the filler

    BYO suggests soaking the filler in a cleaner such as PBW after each use, then rinsing with hot water, so beer does not dry inside the valves.

    Five Star PBW Alkaline Cleaner, 1 lb

Pressure and carbonation numbers

8–12 psiTypical fill pressure, about the keg’s conditioning pressureBYO
2–3 psiOvernight pressure bump some brewers use before bottlingBYO
5–10 sTarget fill time per bottleBYO
3.0 volRough upper limit for standard 12 oz bottlesBYO priming chart
Close-up of chrome beer faucets on a stainless panel
Cold, carbonated beer foams least when filling bottles.Photo: kvanhorn, CC BY 2.0, via Flickr

Your bottles end up at the keg’s carbonation, less a little lost in filling. Use the keg carbonation chart to set it and the carbonation guide to choose a style target. Standard bottles are not meant for very high carbonation; weizens and some Belgian styles above about 3 volumes need heavier bottles.

CO2 volumes by style family (bottle or keg)

Style familyVolumes of CO2Bottle-safe?
British ales1.5–2.2✓ standard bottles
American ales2.2–3✓ standard bottles
European lagers2.4–2.6✓ standard bottles
American lagers2.5–2.8✓ standard bottles
Belgian ales2–4.5~ standard bottles only to about 3 vol
German weizen2.8–5.1~ standard bottles only to about 3 vol

Style ranges: BYO: Carbonation priming chart. Standard 12 oz pry-off bottles are not meant for more than about 3.0 volumes. Bottle only after the gravity reads the same 2–3 days in a row.

Bottles for competitions, growlers and cans

Most homebrew competitions ask for plain brown or green bottles without raised logos or labels, often 10–16 oz, with blank or blacked-out caps; the entry rules list exactly what they accept and how many bottles per entry. Keg-filled bottles suit this well because they arrive clear and fully carbonated with no yeast cake to stir up in shipping. Fill an extra bottle and open it a few days later: if it is already flat or foamy, adjust your technique before the real entries go out.

Taking homebrew to a competition or club event is allowed under federal rules, which permit removal for organized affairs, exhibitions and competitions; state transport rules vary. See is homebrewing legal for the citations.

Growlers

A growler filled from a picnic tap is fine for the same evening. If you want it to keep for a few days, purge it with CO2 first and fill from the bottom with a counter-pressure filler or a beer gun; once opened, drink it that day. Carbonated growlers with their own CO2 cap are another route for parties.

Cans

Canning homebrew needs a seamer and the right can ends; automated fillers like the KegLand Cannular handle the fill step on 110–120V power with a pinch valve and regulator, per the listing. The same rules apply: cold beer, CO2 purge, quick close.

Why oxygen matters more than carbonation

Bottle-conditioned beer has live yeast that soaks up some of the oxygen picked up at bottling. A keg-filled bottle has very little yeast, so whatever oxygen goes in stays in and slowly turns hop aroma dull and malt papery. That is why every method above starts with a CO2 purge, and why capping on foam and oxygen-absorbing caps are worth the extra step for beers you want to keep more than a couple of weeks.

Nitro beer basics

Nitro stouts are served with beer gas, a nitrogen and CO2 blend (often 75/25), through a stout faucet with a restrictor plate. Beer gas cylinders use a different valve than CO2 cylinders, so they need a nitrogen regulator; the regulators in the catalogue are listed with a CGA-580 inlet. Do not use a CO2 regulator on a nitrogen or beer gas cylinder.

Bottling a nitro beer from the keg does not reproduce the cascade you get from a stout faucet, so most brewers serve nitro on draft only.

CO2 cylinders and pressureKeep cylinders upright and secured, and always use a CO2-rated regulator (US CO2 tanks use the CGA 320 valve fitting); never connect a cylinder straight to a keg. Store tanks cool and away from heat. CO2 displaces oxygen and collects low: ventilate, close the tank valve and leave the room if a tank leaks. Never exceed a fermenter’s or keg’s rated pressure.Source: Kegco: Everything you need to know about CO2; OSHA hazard bulletin on CO2

Mistakes to avoid

  • Bottling warm beer. Everything foams; chill keg and bottles.
  • Skipping the CO2 purge. The beer looks fine for a week, then tastes papery.
  • Leaving headspace huge. BYO notes that a smaller headspace reduces carbonation loss.
  • Cranking pressure to speed up the fill. Higher pressure without balance just makes foam; never exceed the keg’s or filler’s rating.
  • Storing filled bottles warm for months. Keg-filled beer is best kept cold and drunk fresh.
  • Forgetting the gas side. Turning off the gas between bottles or running the cylinder low mid-session changes fill pressure and causes foam; check the tank gauge before you start.
  • Not labeling. Mark each cap or bottle with the beer and fill date; keg-filled bottles all look alike in the fridge.

Which filler should you pick?

If you bottle a few competition entries a year, a basic counter-pressure filler is enough. If you regularly fill a case for friends, a beer gun or a faucet-mounted filler is quicker. If you have forward-sealing faucets, a faucet-mounted filler saves a gas line. For bottling a whole batch you never kegged, use priming sugar instead: see how to bottle homebrew. Entering competitions? See homebrew clubs and competitions and the bottling category.

Know what’s in the glassHomebrew is often stronger than commercial beer. One US standard drink is 14 g of alcohol: 12 oz of 5% beer or 5 oz of 12% wine. Brewing and drinking are for adults 21 and over; never drink and drive.Source: NIAAA: What is a standard drink?

Gear picks for this guide: best beer guns and counter-pressure fillers and best bottle cappers.

Priming sugar calculatorHow much corn sugar, table sugar or DME to prime homebrew: CO2 volumes by style, residual CO2 from the…Keg carbonation chart and PSI calculatorKeg carbonation chart and calculator: regulator PSI by beer temperature and CO2 volumes, with an altitude…

Questions

Can you bottle beer from a keg?
Yes. A counter-pressure filler or beer gun purges the bottle with CO2 and fills it from the keg so the beer keeps most of its carbonation. No priming sugar is needed.
Is a beer gun better than a counter-pressure filler?
Neither is better for everything. Counter-pressure fillers control pressure in the bottle and suit highly carbonated beer; beer guns are simpler and faster for routine bottling of very cold beer.
What pressure should I bottle from a keg at?
BYO’s guidance is roughly the keg’s conditioning pressure, often 8–12 psi, with very cold beer and bottles. Never exceed the keg’s or filler’s rating.
How long does keg-bottled beer last?
Kept cold and well purged, it stays fresh for weeks; oxygen pickup is what limits it. Keg-filled bottles have no yeast to scavenge oxygen, so drink them fresh.
Do keg-filled bottles need priming sugar?
No. They are already carbonated and ready to serve. Adding sugar would raise the pressure and risk bottle bombs.
Do I need special bottles to fill from a keg?
Standard 12 oz pry-off bottles work for normal carbonation levels up to about 3 volumes. Use heavier bottles for highly carbonated styles, and check competition rules for bottle size and color before you fill entries.
Can I bottle nitro beer from a keg?
You can fill bottles, but the nitro cascade comes from the stout faucet’s restrictor plate, so the result in a bottle is not the same. Most brewers serve nitro on draft.

Sources

  1. BYO: Counter-pressure bottling techniques
  2. BYO: Carbonation priming chart
  3. Kegco: Everything you need to know about CO2
  4. Brewers Association: Draught Beer Quality Manual (free PDF)
  5. NIAAA: What is a standard drink?