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The reasons customers return their pints.

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All beer is create with a complexity of flavours and as we all perceive this flavour differently, you might like lemon in your Sol or Corona, I may not and will look at you as though you have just crawled out of a sewer and want a hug!

We also have higher sensitivities to certain flavours creating a standard of what we find enjoyable or objectionable. But, there is almost universally agreed upon group of flavours that can be considered “off” when tasted and nowhere is this more unacceptable than in beer.

Here are some of the most common, but there are a lot more.

Lightstruck (3-methyl-2-butene-1-thiol)

Lightstruck is the most common off-flavour that ruins beer and is often perceived as: skunky or sulphuric. This off-flavour only occurs in finished beer and for consumer’s it has become part of the flavour profile of many well-known imported beers due to poor handling, shipping, and storage and will get worse with age, speeding up, if the beer is not stored in darkness.

That’s because Lightstruck is caused by a chemical reaction between daylight or artificial light, riboflavin and hop alpha acids. Some breweries use modified hop alpha acids which do not react with riboflavin, allowing them to continue to use their signature green or clear bottles (buying beer in cans or brown bottles is best, so if your beer of choice comes in clear or green bottles, store carefully and in darkness.

When drinking a beer keep your bottle or glass out of direct sunlight especially if it’s heavy on the hops. It takes a very short time to start the reaction and once started there’s no way to stop it.

Keep homebrew away from light, regardless of whether it is fermenting or packaged.

Pack up your homebrew in kegs or brown bottles. These bottles only let in 5-30% of light through, while green glass allows 50-80%, and clear glass allows a whopping 90% through.

An example would be either Corona or Heineken, two commercial beers that have the Lightstruck feature, with many drinkers assuming this is part of the profile.

Dimethyl Sulfide (DMS)

Often Identified As: Sweetcorn, Cabbage, Cooked, Canned Vegetables, Oysters, Sea Vegetables, Tomato Sauce.

This thought of as an off flavour in nearly all beer, but does have a role in the flavour profile of some pale lagers, German and American pilsners, and cream ales. It will also likely decrease with age.

It’s caused when grain germinates during the malting process. S-methyl methionine, or SMM changes to DMS during the boil. It can also come from wild yeast or bacterial contamination during fermentation.

Rolling Rock is a commercial beer that has DMS as part of its flavour profile.

Diacetyl (2,3-butanedione)

This off flavour is perceived as a Buttery, milky, oily, or buttermilk flavour.

Minor levels may come across as almost caramel, while higher levels or more buttery or butterscotch, like popcorn from the cinema, giving a milky or slick sensation on the palate. It is easier to notice in light lagers.

While it is generally considered an off flavour, in some styles, and at lower levels, it is part of the profile; English bitters, Scotch ales, dry stouts, and Czech pilsner for example. It is caused by non-reabsorption of yeast or over production through weak or short boiling, low temperatures during fermentation, mutated yeast, or racking too early. It can be formed by bacteria contamination too.

Pilsner Urquell is a commercial example that has diacetyl as part of its flavour profile.


Acetaldehyde is extant in all beers at some level. It is part of the flavour profile of certain styles, such as Bière de Garde and American lagers.

Its off flavour can be described as bruised apples, squash-like, latex paint, rough, mistaken for this off-flavour are sweet apple esters and sourness.

Its causes are evidenced by yeast during fermentation as a precursor to ethanol, it can also be caused by oxidation, whereby too much O2 exists in packaged beer, changing ethanols back to acetaldehyde.

As part of its flavour profile, Budweiser contains low levels of acetaldehyde.

The problem though is more than one of detection, but more to do with money. Do you simply take the customer’s word at face value and replace the pint, or do you remove the beer entirely, return it to the supplier and demand a refund?

Identifying what the off-flavour is, could save you both time and money.

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