Equipment
Draught cider from keg to glass
Why does draught cider sometimes taste flat, foamy or sour?
In short
Usually because of the dispense system, not the cider. Gas pressure and temperature together set how much carbon dioxide stays dissolved, so a keg held at the wrong pressure for its temperature goes flat or foams. Air in place of the proper gas stales it. And a line that is not cleaned often enough grows bacteria that make it taste sour, vinegary or buttery.
The reference for all of this is written for beer. The Brewers Association’s draught manual covers the physics and hygiene of a draught system, and those are the same for a carbonated cider. Its frequencies and figures are beer guidance, and they are labelled that way below.
Described in full
- Shape
- Five stages in a column, top to bottom in the order the cider meets them, each with a dashed box to its right naming what can change the cider there.
- Gas
- The gas fills the keg as the cider leaves it, so whatever is in the gas reaches the cider. Air brings oxygen; the Brewers Association manual says compressed air should never be used, because it stales beer within hours.
- Keg, cold
- At a given temperature, the gas pressure on the keg decides how much carbon dioxide stays dissolved. Change either and the carbonation drifts: too little pressure for the temperature and the cider goes flat in the keg; too much and it gains gas and foams.
- Coupler
- Where the line meets the keg. Its seals and check valve are scrubbed at every line clean; a failed check valve can let product back into the gas line.
- Line
- Where most problems start. Product left in an uncleaned line grows bacteria and yeast; vinyl tubing is porous and lets gases in, which is why long runs use barrier tubing. A line that has carried cider may carry its flavour into the next drink.
- Tap and glass
- The nozzle should never touch the glass or the drink. A glass with a film on it strips the bubbles and makes a lively cider look flat.
- What it does not show
- Numbers. Pressure depends on the cider’s carbonation, its temperature and the system’s resistance, and the manual itself warns against setting a system from a table.
What the gas is doing
The gas does two jobs. It pushes the cider out, and, because it fills the keg as the cider leaves, it sits on the cider for as long as the keg lasts. At a fixed temperature, the pressure of carbon dioxide on the cider decides how much stays dissolved. Hold both steady and the carbonation holds. Warm the keg, or lower the pressure, and gas comes out of the cider; cool it, or raise the pressure, and the cider takes more in.
That is why turning up the gas to make a slow tap pour faster is a mistake. The manual says it overcarbonates the drink, which then foams. The fix for flow is the system’s resistance — line length and diameter — not the pressure on the keg.
Long runs in bars often use a blend of carbon dioxide and nitrogen. Nitrogen barely dissolves at dispense pressures, so it adds push without adding fizz. But the carbon dioxide share still sets the carbonation, so a blend chosen for one product can slowly flatten or over-gas another. A cider served through a system set up for beer is served at the beer’s settings unless someone has changed them.
The line is where it goes wrong
The manual calls poor hygiene the number one preventable cause of off-flavours in draught beer. A film of product left in a line feeds bacteria and yeast, and they grow fast. Aerobic bacteria give sour and vinegar notes, anaerobic bacteria buttery and caramel ones. A sweet cider gives them more to feed on than a dry beer does.
The manual’s routine for beer is a line clean every 7 to 14 days, the Association recommending 14, with the coupler scrubbed at each clean. Every three months comes an acid or chelating clean to remove mineral deposits. Chlorine is never used for routine maintenance. Vinyl tubing is porous and is replaced every one to two years; long runs use barrier tubing that keeps oxygen out.
- Give cider its own line. The manual warns that ciders, flavoured beers and wines may permanently contaminate a line and possibly the lines bundled with it; the flavour moves both ways.
- Clean on a schedule and record it, not when the drink starts to taste wrong. By then the line has a biofilm.
- Never push with compressed air. The manual says the oxygen in it stales beer within hours, and a cider has no more defence against oxygen than a beer does.
- Keep the cider cold all the way to the tap. A line that warms between the cooler and the bar is a line where gas breaks out and the pour foams.
Reading a bad pour
The table is built from the beer manual’s off-flavour and system chapters. No study of draught faults in cider specifically was found. The mechanisms are the same; how quickly a given cider shows them is not documented.
| What the drinker notices | Where to look first | Why |
|---|---|---|
| Flat in the glass, keg not empty | Gas pressure against temperature; the glass | Too little pressure for the temperature lets gas out of the cider; a film on the glass strips bubbles |
| Foams, mostly head | Keg or line too warm; pressure raised to speed the pour | Warm cider releases gas; extra pressure overcarbonates |
| Sour or vinegary | Line and coupler hygiene; air in the keg | Aerobic bacteria in a dirty line; oxygen feeding acetic bacteria |
| Buttery or caramel | Line hygiene | Anaerobic bacteria in an uncleaned line |
| Tastes of another drink | A shared or previously used line | Flavoured products can permanently contaminate tubing |
| Stale, papery, tired | The gas supply; how long the keg has been on | Oxygen from air or a leak; age after tapping |
Cask, bag and keg are different systems
Everything above is about a sealed keg pushed by gas. A vented cask or a bag-in-box served by gravity is a different system: nothing pushes the cider and nothing holds carbonation, so it is still cider by design. A vented cask lets air in as it empties, so its life once tapped is limited by oxidation and acetic spoilage, and a bag collapses as it empties, so it does not. The serving and storage topics for bulk containers cover those in detail.
The glass and the pour
A glass that is not properly clean ruins a draught cider faster than anything in the cellar. The manual gives three tests for a clean glass. In the sheeting test, water should coat the inside evenly, not break into droplets. In the salt test, salt should stick evenly to a wet glass. And a clean glass leaves rings of lacing as it is drunk. The nozzle should never touch the glass or dip into the drink, because a nozzle carries dried product and the organisms living on it.
Also answered on this page
Questions this page covers, so you can tell at a glance whether it is the one you want.
- Why is my draught cider flat?
- How often should cider lines be cleaned?
- Can cider share a line with beer?
- Why does draught cider foam?
Related
What people ask next
Questions readers ask about the things this page mentions. Each one goes to the section that answers it rather than to a page written to receive the question.
- What are carbon dioxide, nitrogen and argon used for in cider making, and how dangerous are they? — Air is what damages finished cider, and the cheapest way to remove air is to displace it with a gas that will not react with the cider. That is the whole purpose of inert gas in a cider house.
- What temperature should cider be served at? — Roughly 8 to 12 °C suits most cider: cold enough to be refreshing, warm enough that aroma survives. Tannic, still, complex ciders show better towards 12 to 14 °C; sweet sparkling ciders are usually served colder.
- Why does my cider taste like vinegar? — Acetic acid bacteria have reached the cider and, given air, are converting its alcohol into acetic acid. The cause is almost always oxygen — an unfilled vessel, a leaking bung, or a slow transfer.
- Does the shape of the glass actually change how cider tastes, or is it just tradition?
- What do caustic and acid cleaners actually do, and how are they handled?
- What kinds of keg are used for cider and how do the fittings work?
Sources
What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.
Draught Beer Quality Manual, fourth edition
Brewers Association, Draught Beer Quality Subcommittee (2019); free PDF linked from the Association’s own page · specialist organisation · passage verified 2026-10-29
How this source was checked
Written for beer. Cited for the physics and hygiene of a draught system, which are the same for a carbonated cider, and labelled as beer guidance wherever a frequency or a figure is given. Its pressure tables are not reproduced: the manual itself says not to set a system from them.
National Association of Cider Makers
NACM · specialist organisation · retrieved 2026-08-24
How this source was checked
The UK trade association. Useful for industry-agreed definitions and for the voluntary labelling standards its members work to. A trade body has an interest in how its product is described, so CiderHQ cites it for what the industry says about itself rather than for neutral scientific claims.
Cider and perry production technical training material
Peter Mitchell / Cider and Perry Academy · reference work · registered as competent for this subject
How this source was checked
Searched again on 2026-08-25 and it remains the one printed source here that a bibliographic check cannot fix, because it is not a published work with an edition. It is course material issued to participants of a training programme, so there is no catalogue record to verify, no ISBN, and no lawful public copy. Its state stays `registered` for that reason rather than through inattention.
Where to go next
- Cider making equipment — The rest of the equipment material, grouped by what each piece is for.
- How cider is made — The methods this equipment exists to carry out.
- Troubleshooting — The faults that are traced back to equipment and to cleaning.