A mark of a good brewer versus an average one is in their ability to identify and control the amount off flavors in beer they produce. It should be noted that we said control and not eliminate, this is due to the fact that some of the beer off flavors are actually a desirable trait depending on the type and style of beer you are brewing.
There are many varieties and subvarieties of beer styles, and each has its own complex flavor makeup. Some people will enjoy one style of beer while another will not even be able to drink it. We all recognize and enjoy flavor profiles differently, what you might consider to be delicious your drinking buddy might turn their nose up at. However, when it comes to brewing there are guidelines in place when it comes to certain flavors that are considered to be off-flavors.
Some of these off flavors are actually present in the majority of beers but only to what is considered an acceptable degree, when their levels surpass the acceptable degree they quickly go from being an integral part of the flavor make up to overpowering and are labeled as an off flavor.
Fruity esters are off flavors that are typically acceptable to larger degrees in some styles, whereas a buttery off flavor is only acceptable in very small amounts in certain lagers and typically never in ales. And it goes without saying that the very unpleasant baby vomit off flavor is never acceptable to any degree in any style.
What Causes Beer Off Flavors?
Learning what causes these off flavors and how to prevent them does take time and hands-on practice. Many people believe making beer is a simple process and while it is not difficult to make beer, learning how to make good beer takes time and experience.
The majority of off flavors in beer are as a result of contamination. Learning the best practices for the sanitation of your equipment and brewing space will greatly reduce the chances your beer is exposed to off flavor producing contaminants.
The remaining off flavors are typically caused due to poor brewing techniques or not paying attention to detail. Examples of poor techniques that can cause off flavors are:
- Not boiling your wort long enough.
- Pitching your yeast when the wort is too hot or too cold.
- Fermenting your wort in an environment that is either too hot or too cold.
- Allowing your beer to become oxygenated either during fermentation, while racking, or packaging (bottling or kegging).
- Waiting too long to transfer to a secondary or bottles and kegs.
Learning what causes the off flavor you are experiencing in your beer allows you to fix the problem and prevent it from happening in future beers. The first step in this process is being able to identify the off flavor itself.
Identifying Beer Off Flavors 
Being able to identify the off flavors in beer takes practice. There are two main ways you can learn to identify them.
The first is simply by tasting your beer and others, noting the different tastes you are experiencing, and then doing some research using an article like this where we list all of the common beer off flavors.
If you notice a skunk-like taste or even aroma you can reference this article, scroll through the different off flavors, determine which one produces the skunk-like flavor, learn what causes it and how to prevent it from happening in your next batch.
The second option is to order a flavors standards testing kit. These kits come with little samples of all of the common off flavors, you mix them in a beer and then sample them in order to get an understanding of what the off flavors taste like. It is recommended to use a commercial lighter lager with these kits, this allows the off flavor to really stand out.
Common Off Flavors in Beer
The following are the 20 most common off flavors you will come across.
1) Chlorophenol
Tastes or Smells Like:
Most people describe it as having a plastic-like taste while some perceive it as tasting like Iodine.
Caused by:
Typically this is a result of using water that contains chlorine. If your water supply comes from a city or town there is a good chance it will contain chlorine and you can run into this problem.
Other times this flavor is a result of the cleaning or sanitizing agent you are using on your equipment.
Some yeasts can also produce this flavor, in particular the wild varieties.
How to Prevent:
The simplest way to prevent this off flavor in your beer is to not use chlorinated water. If your water supply has chlorine in it then opt to buy spring water instead.
If you decide to use your chlorinated water, attempt to remove the chlorine with a water filter or by boiling the water for 10 – 15 minutes and letting it cool on its own to room temperature, this will cause the chlorine to evaporate. Most brewers who have chlorinated water will do this the night before brew day and by morning the water will have cooled to room temperature.
Use the correct amount of cleaners and sanitizers. Be sure to rinse your equipment well afterward, when rinsing use pre-boiled water, this makes sure the water you are rinsing with is sanitized. If you are using a no-rinse sanitizer like star san be sure to not exceed the recommended amount.
2) Strong Alcohol Flavor
Tastes or Smells Like:
This off flavor has a very strong and in many cases overpowering alcohol-like taste and aroma to it. You will hear some brewers describe the beer as being hot when they taste it, which basically means very strong in alcohol flavor. Its taste is often compared to paint thinner.
Caused by:
Typically this is caused by fermenting your beer at too warm of a temperature, anything above 80℉ can result in this off flavor occurring. When fermented at these higher temperatures fusel alcohols like butanol, propanol, and phenolic alcohols like tyrosol can develop resulting in the “hot” flavors.
Other causes for these sorts of alcohols developing can be leaving the fermented beer on the yeast bed (trub) for longer periods of time, and if your beer becomes oxidized it can also develop these sorts of flavors.
How to Prevent:
Keep your fermenting temperatures below 80℉ and preferably between 64 – 75℉. We always keep ours at the lower range as a result of having lost one batch due to fermenting too hot.
If you are going to keep your beer in a fermenter for over 2 weeks it is recommended to move it off the trub by racking it to a secondary fermenter. Contact with the trub for any longer than 2 weeks can cause this off flavor and others.
3) Cider
Tastes or Smells Like:
This is that homebrew twang people talk about. It creates a flavor similar to that of an apple or apple juice.
Caused by:
Acetaldehyde which we have already discussed can be one of the causes of this off flavor in your beer. See the section on how to prevent acetaldehyde.
Another main cause is the use of too much cane sugar in your beer. Any more than 1lb of cane sugar in a 5-6 gallon batch and you are running the risk of producing cider-like flavors.
How to Prevent:
You can either cut back on the amount of cane sugar you are using or you can substitute it with a different type of sugar. Many people will either use honey, dried malt extract (DME), or liquid malt extract (LME) instead as they do not produce cider or apple juice-like flavors.
4) Acetaldehyde
Tastes or Smells Like:
Typically people will perceive Acetaldehyde as being like either freshly cut up pumpkin, a rotten apple, or even green apple.
Caused by:
This off flavor can be caused by 3 things:
It is naturally produced by the yeast during fermentation.
It can also occur if the beer gets oxidized by being exposed to too much oxygen when you are packaging it in either kegs, bottles or cans.
And lastly, if it becomes infected some bacteria can produce the green apple-like taste.
How to Prevent:
Acetaldehyde is typically converted into Ethanol alcohol, if you allow the beer time to condition properly this will typically happen and the off flavor will be prevented.
Make sure you are using a good quality yeast and that it is healthy (check the expiry date).
Do not allow the beer to become oxygenated after fermentation has started. This includes not aerating the wort after it has started to ferment and be careful during transfers to secondary fermenters and packaging.
Let your beer condition on the yeast bed for a few days after fermentation has completed. We typically recommend leaving your beer sit for 10 – 14 days in the fermenter.
5) Astringent
Tastes or Smells Like:
Some describe it as tasting like vinegar while others find it has a very tart puckering taste to it.
Caused by:
The number one cause of astringency is what is referred to as tannins. Tannins are found in many plants and their whole purpose is to deter wild animals from wanting the plant or its fruit by making them unpalatable.
Think about the taste and unpleasant sensation you get in your mouth from biting into an unrip plum or pea, that is a result of the tannins. These tannins can also be found in the husks aka skins of the grain used to make beer.
If your mash pH is in excess of 5.2 – 5.6 this off flavor can develop.
If the grain you use has been crushed or milled too fine it can also cause tannins to be released into the beer.
If you use an excessive amount of hops it can also result in this flavor being present.
How to Prevent:
Be cautious about how fine you mill your grains. Brewers tend to want to mill fine in order to get as much efficiency as possible, however too fine and you run the risk of increasing the amount of tannins in the beer.
Strive to crack the grain open and not crush it. As long as you are not milling the grain into powder you should avoid this problem. If you find you are getting an astringent flavor in your beer trying not milling your grain as fine next time.
If you are adding fruit to your beer, do not add it to the boil as this can release the tannins in its skin, instead, you can add it after you have cooled the wort or directly into the fermenter.
When it comes to adding hops pay attention to the different hop varieties you are using, and keep the amount in the proper range for that style of beer.
6) Diacetyl
Tastes or Smells Like:
Most commonly described as having a flavor like that of popcorn you would buy at the movie theaters. Some describe it as having an oil slick-like feel on your tongue, while others will pick up hints of butterscotch.
Sometimes small amounts of diacetyl are a desired flavor in different varieties of ales, however, in all lagers, it is considered to be an undesirable off flavor.
Caused by:
Diacetyl is produced by yeast during fermentation there is nothing you can do about it being produced. However, healthy yeast also reabsorbs it into its cells.
Diacetyl may be present and not be reabsorbed if the yeast is high flocculating or of poor quality and simply too weak.
Not oxygenating the wort properly when you pitch the yeast can cause it and so can fermenting at too low of a temperature.
How to Prevent:
The key is to always use good quality yeast. If you find you are getting this off-flavor on a regular basis consider using a yeast starter.
When it comes to oxygenating the wort, you do not have to go overboard. Simply allowing the wort to splash around while you fill the fermenter typically provides enough oxygen. You can also give it a quick stir which will expose enough oxygen to it.
Be sure to ferment at the proper temperature ranges indicated on the yeast sacket and leave the wort to sit on the trub for a few days after active fermentation has finished. We recommend a total fermentation time of 10 – 14 days. This gives the yeast adequate time to clean itself up and reabsorb the diacetyl.
7) Medicine Like
Tastes or Smells Like:
Most people will say this has a medicinal flavor to it, like cough syrup. Others will perceive it to be like mouthwash, smokey, or even having a clove or spicy taste.
Caused by:
Medicinal tastes are caused by what are referred to as phenols. Phenols can be present in tap water and sanitizers that contain chlorine.
Some specialty yeasts and wild yeast can cause these types of flavors.
Incorrect brewing procedures such as using too much water, and not watching your temperatures during sparging can also cause them.
How to Prevent:
Following the same methods, we explained for preventing Chlorophenol off flavors will usually prevent this one. As well as making sure you are mashing and sparging properly and using the right type of yeast for the style of beer you are making.
8) Fruity or Estery
Tastes or Smells Like:
Strong fruit flavors that are not typical for the style of beer, presenting usually as banana, while sometimes also as raspberry, strawberry, grapefruit, and pear.
Caused by:
Esters are created during fermentation. Some varieties of beer are actually expected to have these flavors present. Examples where ester flavors especially that of banana are acceptable are German wheat beers such as Hefeweizen and many Belgian beers.
In beers where these fruit-like flavors are not appropriate, they are usual a result of fermenting the beer at too high of a temperature. The higher the temperature the higher the chance of the yeast producing more of these off-flavors.
Other reasons these flavors can be produced are not oxygenating the wort enough when you first pitch the yeast and also not pitching enough yeast, which is referred to as under pitching.
How to Prevent:
The first way to prevent fruity esters is to ensure you are using the right strain of yeast for the beer you are brewing. If you are not brewing a German or Belgian style beer it is best to stay away from yeast strains made for those styles of beers as they will produce banana-like flavors.
Make sure you are using the right amount of yeast for the style of beer you are brewing, if you are making a higher gravity beer you will typically need to pitch more yeast than a beer with a standard gravity.
Strive to keep your fermentation temperatures between 60 – 75℉. Your packet of yeast will tell you what its ideal temperature range is. If you find you are producing beers with high levels of ester flavors, try lowering your temperature some. You can ferment closer to 60℉, however, doing so can slow the fermentation time down and you may find you end up with a stuck fermentation.
9) Grass
Tastes or Smells Like:
This off flavor smells identical to what your lawn smells like when you have just mowed it. Some will say it also has a musty flavor to it.
Caused by:
The grassy or musty taste and smell is a direct result of the ingredients you use having gone bad. If bacteria or mold have formed on your grains it can result in this flavor being produced.
The same goes for the hops you use, although they will typically not develop mold, they can produce this off flavor if they are not packaged and stored the right way.
Homegrown hops that are not processed correctly are another cause.
How to Prevent:
Always purchase top-quality ingredients.
Milled grains should be used within 1 month. Milling directly before brewing is the best policy.
Store your grains in a location that is dark, dry, and cool.
Store your hops in a fridge if possible.
If you grow your own hops learn how to process them properly.
Before brewing always take a good look at your ingredients, if they look, smell, and taste fine you should not have any problems with this beer off flavor.
10) Grainy or Husky
Tastes or Smells Like:
For the most part, these types of off flavors will come through as raw grain or fresh wheat.
Caused by:
There are a few potential causes of this off flavor. Newer grains that were not given a long enough rest phase. Over milling the grain to fine, mashing for an extended period of time as well as sparging with overly hot water.
How to Prevent:
Don’t mill your grains overly fine.
Your mash should not go any longer than 2 hours, 1 hour is plenty.
Do not sparge with water that is hot than 170℉
Ensure any homemade malt is allowed 2-4 weeks to age before using
Like with many of the off flavors cold crashing for a few days will help get rid of them.
11) DMS (Dimethyl Sulfide)
Tastes or Smells Like:
The majority of people will detect DMA as having an aroma similar to cooked sweet or creamed corn. Some perceive it as being similar to other cooked vegetables such as tomatoes or cabbage, while others pick up hints of shellfish, milk, and even ketchup.
Caused by:
DMS is actually converted from SMM (S-methyl methionine) when the grains are heated. SMM is an organic compound that is created during the malting process of the grain. Some malts such as Pilsner and 6 row have higher levels of SMM, which can lead to higher levels of DMS.
How to Prevent:
DMS evaporates during the boil. This is why it is important to boil your wort for a min of 60 minutes and to make sure the boil is a strong rolling boil.
If you are using Pilsner or 6 row it is advised to boil for 90 minutes due to the higher amounts of DMS being present.
Do not cover your kettle during the boil, as this prevents the DMS from being driven off through evaporation.
Cooling your wort to pitching temperatures as quickly as possible also helps prevent more DMS from building up after the boil.
12) Metallic
Tastes or Smells Like:
This off flavor has a strong metal taste, most describe it as being iron-like, others will pick up hints of copper or rust.
Caused by:
Many times this is a result of the water you use for brewing containing high levels of iron. Allowing your wort to come in contact with metals such as iron and aluminum during the brewing process can allow these flavors to leach into it.
How to Prevent:
If you have high levels of iron in your water, either treat the water beforehand or consider using spring water you purchase from a store.
Check your containers to ensure that none of their parts have started to rust or corrode.
Ferment in either glass, food-grade plastic, or stainless steel containers.
It is recommended to boil your wort in stainless steel pots. Aluminum is usually fine as long as the water has a pH of under 9.
13) Skunky
Tastes or Smells Like:
Just as the name suggests, it smells just like a skunk.
Caused by:
It is caused by a reaction that is referred to as lightstruck and it only occurs in finished beer. Lightstuck happens when beer is exposed to sunlight or artificial light.
The UV rays cause a reaction between the riboflavin, the hop alpha acids, and the hydrogen sulfide. This reaction creates a chemical called mercaptan which is also what skunks spray and why the smell is so similar.
Beers that are stored in green or clear bottles are known for this off flavor. There are examples of commercial beers that are known for this flavor and allow it to be created intentionally, two popular examples are Heineken and Corona.
How to Prevent:
If you ferment your beer in a clear container like a carboy then keep it out of direct sunlight. Wrapping a towel around it will help.
If you are bottling your beer do use brown bottles instead of green or clear bottles.
14) Oxidation
Tastes or Smells Like:
The most common flavor people get from oxidized beer is an old or stale taste, others pick up wet cardboard or paper.
Caused by:
Oxidation is caused by how oxygen reacts in a negative manner to beer. No matter how the beer is brewed some oxygen is going to be present, the older a beer gets the more apparent its effects become. When excessive amounts of oxygen are allowed to penetrate the beer during the brewing process the sooner these negative effects will appear.
How to Prevent:
It is ok and actually necessary to aerate the wort as you are pitching the yeast. But after fermentation has begun it is important to minimize exposure to oxygen as much as possible.
When transferring the beer to other containers do not allow it to splash around.
Fight the urge to open the lid on your fermenter.
When adding dry hops attempt to minimize the exposure to oxygen as much as possible.
When bottling minimize the headspace, keep it to no more than 1-2 inches.
If you keg your beer, it is smart to purge the keg with CO2 first and once you have filled it with the beer, purge the oxygen that will have built up at the top.
15) Rotten Eggs
Smells or Tastes Like:
Rotten Eggs is what most people pick up from this off flavor, however, some will perceive it to be like a burning match and even raw sewage.
Caused by:
It is caused by hydrogen sulfide and what most people perceive sulfur to smell like. This is a naturally occurring odor that many strains of lager yeasts produce.
How to Prevent:
It is actually rare that this odor will be found in a properly fermented and conditioned lager, as the CO2 during fermentation should remove it and proper conditioning and lagering should prevent it from occurring. Follow proper lager brewing techniques.
If after following proper brewing techniques you find that this odor remains strong in the final product then you might want to try a new strain of lager yeast.
16) Mildew
Tastes or Smells Like:
Beers with this problem have a strong musty flavor or smell, very much like what an old damp basement would smell like. Strong tones of mold, mildew, and must are present.
Caused by:
This is caused exactly as you would think, mildew or mold has formed on your brewing ingredients or on the brewing equipment itself.
How to Prevent:
Make sure that your ingredients are mold and mildew free.
Be sure to clean and sanitize your equipment properly.
Do not store your fermenter in a damp or humid location, always keep it in a dry area.
17) Detergent
Tastes or Smells Like:
This off flavor creates a soapy or detergent-like taste.
Caused by:
It can be created by not rinsing the cleaning agent out well before using your equipment, however, in the majority of times, it is actually created by allowing your beer to sit on the trub in the primary fermenter for too long.
How to Prevent:
Rinse your brewing equipment out well when done cleaning and prior to sanitizing. If you want to rinse after you have sanitized do so with boiled water.
If you are going to age your beer transfer it from the primary fermenter to a secondary. It is recommended not to let your beer sit in the primary fermenter for any longer than 10 – 14 days.
18) Paint Thinner
Tastes or Smells Like:
This beer off flavor resembles paint thinner or even nail polish remover.
Caused by:
This off flavor can be caused by using fermenters that are not food grade.
As well brewers who use the no-chill method and do not use food-grade containers can also experience this off flavor.
An other cause is if your beer became oxidized and then you also allowed it to be fermented at too warm of a temperature.
How to Prevent:
Do not allow your beer to become oxidized and always ferment within the proper temperature range for your yeast. Most yeast packets indicate their ideal temperature range.
Always ferment in fermenters made out of glass, stainless steel, or food-grade plastic.
If you continue to get this off flavor and are using a food-grade plastic fermenter, check its indicated temperature rating and make sure you are not exposing it to liquids that are exceeding it as this can cause the plastic to leach out toxins.
19) Salt
Tastes or Smells Like:
A beer with this off flavor has a very salty flavor, almost like it was mixed with saltwater.
Caused by:
It is caused by adjusting your brewing water incorrectly and either adding too much epsom salts or gypsum.
How to Prevent:
Learn how to adjust your brewing water correctly. Never add the salts to your brew just for the sake of doing so. Get your water tested and know its exact content before attempting to adjust it.
The Final Word
The main way to prevent all of these common beer off flavors is to make sure to clean and sanitize your equipment and brewing space properly and ensure that you engage in good brewing practices.
Be sure to leave us a comment below with your experience on off flavors.
P.S. Also check out the offer to get the recipes for my top 5 best-selling beers from my brewpub, details are on the side of the blog or at the bottom if you are on your smart device.