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A draft system you never clean doesn't just get "a little less fresh". It moves through four predictable stages — and at every one you're paying a real amount, long before a guest ever tastes it.
A guest sends a pint back. "Tastes off tonight." Your bartender smells it, tastes it herself, and decides: this keg's no good. The next keg tastes exactly the same. By the end of the shift you've got three complaints, a supplier swearing there's nothing wrong with the brew, and nobody has so much as looked at the three metres of tubing between the keg and the tap — because it sits inside a cooler, behind a panel, and nobody has ever pulled it apart since the system went in.
That's the problem with a draft line: the fault sits invisibly on the inside, and the clock starts the moment you stop cleaning — not when you notice something's wrong. A line pouring perfectly today is a completely different line in three weeks, even though nobody has changed a single thing. That's exactly why it gets misdiagnosed so easily: the CO2 pressure gets adjusted, the cooler temperature gets checked, the keg gets sent back — everything except the line itself, because it "was only cleaned a few weeks ago", except nobody actually remembers when that was.
And this goes beyond beer. Any line pushing a drink through tubing under pressure — a postmix system for cola and tonic, a wine-on-tap system, a nitro coffee tap — builds up exactly the same problem, at exactly the same pace. A venue with no beer tap at all but a soft drinks system behind the bar has this problem just as much; it's just rarely recognised, because nobody associates a cola tap with "contamination".
This article follows that clock: four stages, from a perfect pint to a keg you've effectively poured down the drain without realising it, each with its own recognisable off-flavour or foam problem. Then the mistake that persists even among bars that DO clean, a calculator that puts a euro figure on what a neglected line costs you, and a routine you can realistically keep up. For the pricing and measurement mistakes on your drinks list itself, see Pour Cost & Beverage Margin — this article is about the physical condition of the line, not what's printed on your menu.
Why the keg always gets the blame
A draft system has no warning light. There's no moment where it flags itself as "dirty" — it just keeps pouring, day after day, until the taste has drifted far enough that a guest notices. By then nobody has a reference point left: was this keg always a bit sharper, or is that the line? Most venues have no answer, because nobody ever wrote down what a genuinely clean pint is supposed to taste like.
On top of that, the symptoms of a dirty line look uncannily like symptoms you already know how to adjust: too much foam gets read as "CO2 pressure too high", a flat beer as "poured too cold", an odd finish as "bad keg". Every adjustment you make in response — lowering the pressure, raising the temperature — hides the problem for a few days instead of solving it, and sometimes makes it worse (lower CO2 pressure gives the line even more chance to go flat and stale between shifts).
And the supplier is rarely the culprit, precisely because it's the easiest thing to check: a keg has a use-by date and a batch number, and nine times out of ten that keg is perfectly fine right up until it leaves your cooler. What happens to it in the last three metres — the tubing, the coupler, the tap itself — falls outside their responsibility and, in practice, outside everyone's attention.
The ultimate guide Menu Engineering & Drinks: 6 Steps to More Margin From list design to pour cost: everything your menu can earn for you, in one guide. Open the guideThe 4 stages of a draft line nobody cleans
A draft line doesn't get dirty in a straight line. It moves through four recognisable stages, each with its own time window and its own specific symptom — and it's no coincidence the industry sticks to a two-week cleaning rhythm: that's exactly the moment stage 3 begins.
The figures below are about beer, because that's where most of the research sits, but the same pattern — biofilm, mineral scale, growing pour loss — applies to any drink poured through a line under pressure.
Day 0 to 3: the perfect pint
Immediately after a thorough clean, a draft line is at its best: a pint at the right temperature, two to three centimetres of stable foam that holds for a few minutes, a pour time of eight to ten seconds, and no off-flavour. This is the reference point most venues never record — which means there's also never anything to measure later drift against.
What few people realise: this state doesn't last, it's a starting point. Every night the system sits idle — after closing, on a quiet day — liquid sits still in the line at room temperature in the uncooled stretch, and that's exactly the environment stage two needs to begin.
Day 3 to 10: the invisible film
Bacteria and wild yeast colonise the inside of a line remarkably fast: research into beverage systems shows a measurable biofilm can form within 24 to 72 hours on a wet surface that hasn't been chemically cleaned. At this stage you can't yet taste or smell anything — the colony is too small to affect flavour — but the clock has irreversibly started.
This is also the stage where the material of your line makes a difference. Stainless steel is smooth and makes it hard for bacteria to attach; the flexible plastic tubing most systems use between keg and tap picks up microscopic scratches over time, and those scratches stay a reservoir for biofilm even after a correct clean. That's why a draft line isn't a lifetime part: most installers recommend replacing the tubing itself — not just cleaning it — every one to two years.
From here the graphic below starts to build: four stages, each with a growing share of pour loss on top of what even a perfect line already unavoidably loses to foam.
Each stage shows the estimated pour loss on top of what even a brand-new line already unavoidably loses to foam.
Pour loss is the share of beer you buy but never serve as a full, sellable pint — foam you tip out, a pint you have to pour again. Figures are an average from systems that aren't extremely neglected; a genuinely blocked or damaged line can run higher.
Day 10 to 21: the tipping point
This is exactly the window where the industry standard of "clean every two weeks" comes from, and the reason is measurable: around day ten to fourteen the biofilm is mature enough to produce its first effects, and each effect has its own recognisable cause. A sour, vinegary aftertaste typically comes from acetic- or lactic-acid bacteria that have settled into the film. A flat, papery or "wet cardboard" taste points to oxidation, often made worse because a rough inner surface holds more air than a smooth line would. A medicinal or plaster-like undertone usually comes from wild yeast that's taken up residence in the biofilm, or from cleaning solution that wasn't fully rinsed out at the last clean.
At the same time the foam problem starts, and it has a physical cause, not just a chemical one: mineral scale — beerstone, a calcium-oxalate deposit built up from hard water and compounds from the hops — clings to the inner surface and roughens it. A rougher surface gives CO2 bubbles far more places to form (nucleation points), which means more foam per pint, a slower pour, and a slowly growing queue at the bar during a busy shift.
Notice these are exactly the symptoms dismissed as "CO2 pressure" or "an off keg" in the previous section — except the window in which they appear lines up exactly with the window in which nobody remembers when the line was last cleaned.
Day 21 and beyond: the wasted keg
Past three weeks the problem is no longer marginal. Pour loss — the beer that never reaches a guest, lost as foam or as a badly poured pint tipped down the drain — stacks up well beyond what even the most careful bar unavoidably loses, and the graphic below puts that difference in euros per year for a single beer line.
The real cost isn't only the wasted beer. Complaints pile up right at the point where nobody recognises the cause any more — the "fixes" from the previous stage (adjusting pressure, adjusting temperature) have already been tried and changed nothing, which makes the problem look like a structural quality issue with the brewery rather than with your own system.
And in most EU member states your draft system falls under the same hygiene self-inspection as your kitchen: an inspector on a routine visit doesn't only look at your walk-in, they also check when your draft lines were last cleaned — and "I can't remember" is exactly the answer that earns a note in the report.
More foam means less sellable beer in that same glass — for one beer line, per year.
The difference between the two glasses isn't cosmetic — it's beer that was bought, paid for, and never sold as a full pint. Work out your own figures in the tool below.
The mistake that persists even among bars that DO clean
Most bars that faithfully clean every two weeks use exactly one product to do it — usually an alkaline cleaner — and then keep wondering why the foam problem always comes back. The answer is that there are two completely different kinds of buildup, and one cleaner only solves one of them.
An alkaline cleaner breaks down organic matter: the biofilm itself, proteins, yeast residue. It does nothing about beerstone — that calcium-oxalate scale is a mineral problem, not an organic one, and needs an acid cleaner to dissolve it. A line that's only ever been cleaned with an alkaline product can be perfectly "clean" in the sense that no bacteria are active any more, and still foam excessively because the mineral scale was never touched.
The rule of thumb most professional cleaning services follow: alkaline clean at every visit, and add an acid clean every four to six visits — or as soon as the foam problem persists despite regular cleaning. It's not an extra step for peace of mind; it's the step that actually fixes the foam problem once alkaline cleaning alone stops being enough.
What a neglected line actually costs you
Enter your own figures below. The calculator estimates pour loss based on how many weeks have passed since the last thorough clean, and turns that into a real amount per year — on top of what even a perfect line unavoidably loses.
The starting values already filled in are the same ones used in Pour Cost & Beverage Margin, so the two articles are talking about the same thing.
Calculate your own pour loss
Three figures, and you'll see straight away what waiting costs you.
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Cost price is estimated at roughly 15% of your selling price — a common share for draft beer. Know your own cost price exactly? Carry on with the calculator in Pour Cost & Beverage Margin instead.
Put that amount next to the cost of cleaning itself — the tile above already shows a full year of professional cleaning beside it. At eight weeks without cleaning, pour loss on its own starts closing in on that yearly cost, and at that point cleaning stops being an expense: it's the cheaper of the two options.
And this still doesn't count the guests who never file a complaint, they just order something different next time — or don't come back. That loss shows up in no cost line anywhere, but it's exactly the loss a happy hour or a beer promotion has to fight against if the first impression is already wrong.
A routine you can actually keep up
A cleaning schedule that only exists in one person's head disappears the moment that person takes two weeks off. So put cleaning on the exact same kind of recurring list as the rest of your building — alongside your opening and closing round and the upkeep of your other equipment (see Kitchen Equipment: Upkeep & Costs for the same principle applied to ovens and refrigeration) — with a name attached to every visit, not just a fixed date.
The rhythm differs per drink. Beer lines: every two weeks, no exceptions, because that's where the biofilm clock is strictest. Postmix and soft drink systems can usually get by on a monthly rhythm — the sugary medium is less hospitable to some bacteria strains, but CO2 pressure and mineral scale still apply just the same. Wine-on-tap and nitro coffee are more sensitive and deserve a check every two to three weeks, even though volume is often lower.
If you clean it yourself with a DIY kit, apply the distinction from the previous section literally: alkaline at every visit, acid added in periodically. If you hire a service, simply ask whether both products are a standard part of the contract — it's a ten-second question that makes the difference between a line that's genuinely clean and a line that only smells like it.
- One fixed day on the calendar, every two weeks, with a name next to it — not "someone will get to it".
- Alkaline cleaner at every visit, acid cleaner every four to six visits or as soon as the foam keeps coming back.
- Postmix and soft drink systems on a monthly reminder, even if nobody's ever complained about them.
- Date of the last clean noted somewhere visible — on the system itself, not just in a diary nobody opens at the bar.
- For a persistent foam or taste complaint: check the line first, only then adjust the CO2 pressure or the temperature.
Taste the problem before it becomes a complaint
A draft system gives no warning. It just keeps pouring, moving a little further into the four stages above every single day, until a guest notices and the wrong part gets the blame.
The only thing that breaks that pattern is a date written down somewhere visible and a clean that doesn't depend on whether someone still remembers. Two products instead of one, a fixed rhythm instead of "whenever it seems necessary" — that's the entire difference between a line quietly eating your margin and a line that does exactly what your menu promises.
Work it out for yourself with the tool above, put the date in the calendar, and read Pour Cost & Beverage Margin alongside it if you also want to re-check the pricing on your drinks list.