There is no greater disappointment after a hard day than to sit down in the pub for a refreshing pint to find that something is not right. Some poor flavours are caused by the brewing process and as a pub landlord are out of your control, but below we have listed some of the most common flavour and odour taints that can occur and that can be prevented.

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These taints are generally caused by types of chemicals called phenols, part of the phenolic group of chemicals, the most common in the pub industry is Chlorophenol. It only takes a very very small amount of chlorophenol to develop within the system to taint the beer, they can taste and smell like antiseptic solutions, mouthwash cleaner or even spicy like cloves.

Chlorophenol taints are thought to be caused by a reaction between the beerline material and beerline cleaners when they are not used correctly. Using more beer line cleaner than the manufacturer recommends or leaving cleaner in the lines for longer than the recommended time can cause damage and a taint to form. The best way to prevent this is to use a good quality beer line cleaner and follow the manufacturers dosing and cleaning instructions.

There are some products on the market which can remove chlorophenol taints from the system, but if the taint is too severe or cannot be removed then the whole python or pipe line will need to be replaced.


An easy to prevent taint if you follow the proper beer line and glass hygiene practices. This form of taint is generally caused by either poor or infrequent line hygiene, which has allowed mold and mildew to get into the dispense system and form bio-film colonies, it can also be formed by the process of pouring slops back into a cask at the end of each session, this should never be done as it is a false economy and ruins the taste of your beverage.

These taints are easy to remove from the system by using a deep cleaning method or calling a cellar services technician, although in the case of a bad infection or one caused by pouring beer back into a cask, the product may have to be disposed of, as the whole cask or keg is ruined.


This is more a flavour taint rather than odour but in very severe cases there can be a faint metallic smell to the beer. A metallic taint alters the way the beer feels in the customers mouth, and has been compared to the taste of a penny coin, blood or sometimes ink. The main cause is ferric sulphate (Iron Sulphate) from rust or non-stainless steel fittings. When the beer comes into contact with an unsuitable metal it removes some of the iron oxide (rust) from the surface of the fitting or container, which then dissolves into the beer. The only way to remove one of these taints is to check that all metal fittings that the beer will come into contact with are made of a suitable material and replace incompatible components, followed by a good beer line deep clean.

Skunk Like

Also known as Light-Struck or Cat Musk aromas, these are mainly found in bottled beers (Green or Clear) which have been stored in direct sunlight or under fluorescent lights for too long. UV light from these sources reacts with the beer to form a chemical called Mercaptan or 3-methyl-2-butene-1-thiol (Smells like natural gas from the cooker as its the same chemical added to natural gas to give it a detectable smell). It tends to effect lighter beers or those with hoppy characteristics. This is prevented by making sure your beer in green or clear bottles is stored out of direct sunlight or fluorescent lighting. Beer in brown bottles tends to be unaffected as the colour of the glass blocks light in the UV spectrum.


Beer which has been oxidised tends to have a musty, wet cardboard/paper type of smell and taste. It is caused by beer that has started to age and there is nothing that can be done to recover the beer. Once a cask has been opened and conditioned it should be emptied within 3 days, and Kegs should be emptied within 3-7 days of connecting to the dispense system, to give the best flavour, after this the beer will have reacted with the air and oxidisation will have occurred causing a chemical to form called Nonenol.

The best way to prevent this type of taint is to follow proper stock rotation and only order keg & cask sizes that can be sold within the recommended period.


Simply put this is another issue of poor line hygiene, and is caused by wild yeasts and bacteria which have managed to invade your beer line system and establish bio-film colonies. These contaminant metabolise within the beer and form acetic acid as a bi-product giving your beer a sour taste and smell. These taints should be treated in the same way as a moldy flavour taint with a deep clean and then follow proper line hygiene standards.


This is often compared to sucking on a used wet teabag with a puckering, dry/powdery feeling in the mouth. This is again caused by poor line hygiene practices. If beer lines are not cleaned often enough then tannin from the beer and bacteria will begin to be deposited on the inner surface of the beer line and fob chamber. Over time if these are not removed then they will slowly change the flavour of the beer. Astringent taints can sometimes be confused with vinegar taints as they can be similar in nature and the bacteria which cause astringent flavours will also create acetic acid. Proper line hygiene with a beer line cleaner suitable to your water hardness conditions and beer type is the key to keeping this style of taint away.


Fruity flavours are common to many styles of beer but when they are overpowering/stronger than normal or develop in beers without the characteristic it can be a sign that a taint has occurred. This flavour is imparted to the beer by yeast during fermentation through the creation of esters such as isoamyl acetate, with different yeasts giving different flavour profiles. If the beer has been contaminated with wild yeasts this can then cause the flavour to become off balance and be unpleasantly strong. Proper beer line hygiene and storage of beer is key here.


This is a wet, damp soil type of flavour, similar to the taste in your mouth after freshly digging the soil when gardening. This is a very serious taint and occurs due to bacteria found within groundwater and damp cellar walls/floors. The nasty part is that the bacteria doesn’t even have to get into the beer line system to impart the flavour taint. Within pubs this is usually caused by poor cellar hygiene and damp conditions, bacteria within the walls produce a chemical called 2-ethyl fenchol which has the ability to pass through the semi-porous surfaces of some packaging and beer line materials into the beer line systems. Good cellar hygiene and regular cleaning will help to prevent this type of taint with proper cellar ventilation helping to reduce the climate that the bacteria thrive in.

If you have any questions about best hygiene practice for your cellar and beer lines just ask our friends at CellarCraft.