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Off Flavours in Beer and How to Identify Them

Updated: Nov 27, 2023

Whether you’ve got a few brews under your belt already or you’re just starting out, one of the most important tasks you need to master as a home brewer is that of identifying when a beer you have brewed is off. It’s easy to tell whether a brew is pleasing to your palate but how can you tell the difference between a batch you’re simply not keen on and one where something went seriously wrong? In all honesty, it’s a skill that can only be developed with practice but the tips below should give you a head start. Common Off Flavours in Beer: How to Spot Them and What to Do About Them Off flavours can arise from issues with either the brewing or the bottling/packaging process. In this article, we’re going to focus on those undesirable flavours that are caused by issues with the brewing process.

Dimethyl Sulfide – If you notice an unpleasant boiled vegetable flavour in your beer, perhaps like cabbage or stewed tomato, dimethyl sulfide is the most likely culprit. This chemical develops in the wort at high temperatures and is present in small quantities in all beer. An excess of dimethyl sulfidemay be caused by poor yeast health or by covering your brew kettle when boiling the wort. Uncovered boiling will get rid of most of it, as will vigorous fermentation. It is a common problem when brewing pilsner and pale malt beers, which you can solve with a longer, uncovered boiling period and by using fresh yeast. Acetaldehyde – This chemical is produced as the yeast in your brew is ridding itself of CO2. Under normal brewing conditions, most of the acetaldehyde should be consumed by the yeast and converted into alcohol but if you rush the fermentation process, too much of it can be left. This results in a noticeable off flavour in your beer that many have likened to wet grass or green apples. Diacetyl – During fermentation, a chemical process known as amino acid synthesis causes diacetyl to leak from yeast cells. If you let your beer rest for long enough, the diacetyl should be reabsorbed by the yeast. However, if you try to hurry things by skipping this rest period, a buttery popcorn taste and a slick feel in the mouth could be the result. The solution, as with acetaldehyde issues, is not to rush your brewing. Ethyl Acetate – Ethyl acetate presents with a fruity aroma at lower concentrations: a desirable quality in certain Belgian brews. However, at higher concentrations it causes a harsh solvent flavour like nail polish remover.The primary cause of high ethyl acetate levels in beer is allowing the temperature to get too high during the fermentation period. You’ll find these off flavours easier to spot as you gain experience but if you run across any unusual tastes that you can’t identify, feel free to get in touch and we’ll do our best to help.


Continuing Exploration of Off Flavours in Beer

As you refine your brewing skills, you’ll encounter various off flavours, each with unique causes and remedies. Here are some additional off flavours to be aware of:

Isovaleric Acid – This off flavour imparts a cheesy, old hop aroma to your beer. It’s often due to the use of stale or poorly stored hops. To avoid this, always use fresh, well-preserved hops and store them in a cool, dark place. If you detect this off flavour, consider reviewing your hop suppliers or storage practices.

Chlorophenols – If your beer has a medicinal, band-aid like smell, it’s likely due to chlorophenols. These compounds can enter your brew through chlorinated water or contaminated equipment. The best way to prevent this is by using filtered or dechlorinated water and ensuring your brewing equipment is thoroughly cleaned and sanitized.

Lightstruck – Ever had a beer that tasted like a wet cardboard or skunk? That’s the lightstruck flavour, caused by exposure of beer to light, leading to a photochemical reaction in hops. Brown bottles and cans can prevent this, as can storing beer in a dark place. If your beer tastes lightstruck, assess your storage conditions, especially if you’re using clear or green bottles.

Metallic – A metallic taste can creep into your beer if it comes into prolonged contact with metal surfaces, particularly those not intended for brewing, like iron or rusty steel. Use stainless steel equipment and avoid contact with non-brewing grade metals to steer clear of this off flavour.

Sulfur Compounds – Sulfur-like aromas, reminiscent of rotten eggs or burnt matches, can occur due to stressed yeast or certain water profiles. Ensuring a healthy yeast environment and adjusting your water profile can help mitigate these odors.

Phenolic – A smoky, clove-like, or plastic-like flavour indicates phenolic compounds. These are sometimes desired in styles like Belgian ales, but unwanted phenolics might result from wild yeast contamination or using chlorinated water. Pay attention to yeast strain selection and water quality to control this.

Remember, the key to mastering off flavours lies in experience and meticulous process control. Each batch you brew brings you closer to becoming a brewing maestro. If you’re stumped by a strange flavour, don’t hesitate to reach out for assistance. Happy brewing, and may your beers be flavourful and flawless!

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