Signs of a badly kept pint at a bar and what to say

Why draught goes wrong

Between the keg and your glass, beer travels through a coupler, lines, a cooling system and a tap. Each part needs to be clean, cold and at the right pressure. Lines that are not cleaned regularly build up yeast, bacteria and beer stone. Kegs stored warm age quickly. Glasses with grease or detergent kill foam.

Draught lines are commonly recommended to be cleaned every two weeks, though practice varies widely. Our guide to draught line cleaning covers how it is done.

Signs in the glass

• No head, or one that vanishes. Often a dirty or greasy glass. Look for bubbles clinging to the inside walls below the surface, a sure sign the glass is not clean.
• Flat beer. Low carbonation can come from gas pressure set wrong, or from a keg that has been open too long.
• Too much foam. A glass of mostly foam usually means the beer or lines are too warm, or the pressure is too high.
• Haze in a clear beer. A pilsner or lager that should be bright but looks cloudy may be infected, old or served from a line that needs cleaning.

Check the pour as well. Our guide to how to pour beer covers what a good pour looks like.

Signs on the nose and palate

Butter or butterscotch. In draught beer this often comes from bacteria living in dirty lines, especially Pediococcus. It can also come from the brewery. If the same beer in a can tastes clean, the line is the likely cause.

Sour or vinegar. Unexpected sourness in a non-sour style points to bacterial infection in the lines or keg.

Stale, cardboard or honey notes. A sign of oxidation, often from a keg that is old or was stored warm. Our guide to oxidised beer explains the flavours.

Metallic or chemical. Can come from line cleaning chemical not rinsed out properly, or from damaged fittings.

Warm beer. Draught lager served well above about 6 °C tastes flabby and sweet. In a hot city with an overloaded cooler, this is common in the evening rush.

Confirm before you complain

Before blaming the bar, ask yourself a few questions. Is this style meant to taste this way? Some English ales are served with a soft, low carbonation. Some styles are naturally hazy. Have you tasted this beer elsewhere recently? Was it different? Is it just one beer, or do several taps taste off?

If one beer tastes buttery or sour and others from the same bar taste fine, the problem may be that keg or line. If every beer tastes slightly off, the bar's system or glass washing is the likely cause.

Timing matters too. The first pour of the day from a tap that has sat overnight can taste warmer or flatter, because beer sitting in the line above the cooler warms up. A good bar pours that off before serving. If your first pint tastes odd and the second is fine, that is probably what happened.

What to say

Be polite and specific. Staff are more likely to help when you describe what you notice rather than declaring the beer bad.

• "I think this one might be a bit off. I'm getting a buttery note. Could you taste it?"
• "This seems quite flat compared with usual. Is the keg new?"
• "There are bubbles stuck to the side of the glass. Could I have it in a fresh glass?"
• "Do you know when the lines were last cleaned?"

Most good bars will taste the beer, swap it for another or pour a fresh one. If they will not, choose a different beer and consider giving feedback later. If you know the brewery, telling them is useful too. Breweries care about how their beer is served and many will follow up with the bar.

How to spot a well-kept bar

Look for clean, cold glasses rinsed just before pouring, beers served with a proper head, bright and lively lagers and staff who know what is on tap. A bar that can tell you when its lines were last cleaned is usually a bar that cleans them.

Learning to recognise these faults with confidence takes practice. A buttery line infection and a brewery diacetyl problem can taste similar. Telling them apart is the kind of skill that structured sensory training with reference samples builds.