Common Odors in Beer Brewing

Causes of Odors

Some odors, especially those caused by contamination, are almost always considered problematic. Although there are occasional wild yeast contaminations that make beer taste delicious. These off-flavors are usually caused by poor sanitation and, in a few cases, improper brewing methods.

My beer tastes like butter

• Odor: Diacetyl

• Chemical name: 2,3-Butanedione

• How to identify: The product smells like butter, buttered popcorn, or butterscotch, with a slippery or creamy flavor on the tongue and in the mouth.

• Cause: All yeasts produce diacetyl during fermentation, which is then "reabsorbed" by the yeast cells. Any diacetyl that is not reabsorbed may be due to strong yeast flocculation, weak or mutated yeast, oxygenation problems, low fermentation temperatures, or short boil times.

Sweet Corn Flavor in Beer

• Odor: DMS

• Chemical Name: Dimethyl Sulfide

• How to Identify: This odor smells like sweet corn, cooked cabbage, ketchup, etc.

• Cause: This compound is produced during the malting process of grains and is converted into DMS when heated. Therefore, it is produced during the production of wort and in smaller quantities during fermentation. This makes DMS more prevalent in lagers and beers, and it can also be produced by bacteria that contaminate beer. DMS can be removed by evaporation when boiling the wort.

My beer has a metallic taste

• Odor: Metallic

• Chemical name: Ferrous sulfate

• Cause: This contamination occurs when beer or ingredients come into contact with poor quality metal pipes or machinery, especially when raw metal is used to cook wort. Wort may also be transported in packaging, such as metal cans, bottle caps, or kegs. Stored grain can also develop a metallic smell.

My beer smells like rotten eggs

• Odor: Sulfide

• Chemical name: Hydrogen sulfide (H2S)

• How to identify: This smell may resemble boiled or rotten eggs, burning matches, or raw sewage.

• Cause: All yeasts produce hydrogen sulfide during fermentation. Lager yeasts tend to produce more sulfur aromas than ale yeasts. Low concentrations of hydrogen sulfide can give beer a "fresh" taste, but high concentrations can cause beer to taste off.

Beer smells like bananas

• Odor source: Esters (isoamyl acetate)

• How to identify: If the beer contains esters, it will smell like bananas or pears. If the beer contains less esters, it may smell like strawberries, raspberries, and grapefruit.

Isovaleric acid is the most common ester flavor in all beers, and the concentration varies in different types of beer. Isovaleric acid is the main flavor characteristic of some lagers and ales. It is also a German wheat beer (Hefeweizens) with the signature flavor characteristics of many Belgian ales.

• Cause: Esters are a byproduct of the fermentation process. Strong or inappropriate fruity flavors in beer are sometimes caused by fermentation temperature. Generally speaking, the higher the fermentation temperature, the more esters the yeast produces. In addition, low oxygen environments are also conducive to the production of esters.

Beer has an off odor

• Odor: Light exposure

• Chemical name: 3-methyl-2-butene-1-thiol/mercaptan

• How to tell: This smell can smell like skunk or brewed coffee. It can also smell musty, like burnt rubber or cat musk.

• Definition: Light-exposed beer is beer served in clear or green glass that develops an off odor when exposed to light. Pale beers and beers with high hop content are more likely to develop off odors. Bitter beers with modified hop bittering acids do not develop this flavor. Dark beers and beers using isomerized hop extracts are less susceptible to light exposure.

• Cause: When hops are exposed to sunlight or ultraviolet light from fluorescent lights, alpha acids break down and react with hydrogen sulfide produced by yeast. This reaction produces mercaptans. Mercaptans are the same chemicals secreted by skunks when they spray, which is why malty beers smell like skunks.

Beer Smells Like Paper

• Odor Source: Oxidation Reaction (Nonanal)

• How to Identify: Oxidized beer smells like old wet cardboard, or has a papery and papery taste.

• What it is: Nonanal is an odor associated with aging beer. This odor becomes more noticeable if steps are not taken to reduce the oxidation process. Introducing too much oxygen into beer (especially when the weather is still warm or after fermentation is complete) can produce a cardboard or sherry-like flavor.

• Cause: Oxidation occurs when oxygen reacts with molecules in the beer. Unwanted splashing of beer that occurs when beer is transferred from one container to another can also cause oxidation in the wort. In addition, too much headspace in the beer bottle can also lead to oxidation.

Musty smell in beer

• Odor: TCA

• Chemical name: 2,4,6-trichloroanisole

• How to identify: This smell is like mold, corked wine, or a damp cellar.

• What it is: TCA is a chemical produced by mold that consumes and metabolizes chlorinated phenols, which can be detected by humans at low concentrations.

• Cause: TCA is produced when beer is fermented in a damp area or grains become moldy during storage, but TCA can migrate through most semi-porous packaging, so cross-contamination can occur at multiple stages of beer production, from raw materials to final packaging.

Beer smells like cloves

• Odor: Phenolic

• Chemical name: 4-vinylguaiacol

• How to identify: This smell and taste has notes of cloves, but also has characteristics of cough syrup, smoke, and some other spices and herbs.

• What it means: A dominant flavor in some ales and stouts, but often considered an off-flavor in bottom-fermented beers. It can be a signature flavor of some beers, including German wheat beers.

• Cause: Phenolic flavors are often due to the presence of wild yeasts or the use of special yeasts during fermentation. Other sources of phenolic flavors can be bacterial action due to poor sanitation and the presence of phenolic compounds in the ingredients.

Beer smells like green apples

• Odor: Acetaldehyde

• How to identify: This stuff tastes and smells like green apples, rotten apples, latex paint, or a cut pumpkin.

• What is acetaldehyde: Acetaldehyde is a chemical produced by yeast during the fermentation process in all beers. It is usually converted to ethanol, but this process can take longer if not enough yeast is used or the beer is higher in alcohol.

• Causes: The off-flavor in beer is caused by insufficient fermentation time, insufficient wort yeast, or low-quality yeast, which does not give the yeast enough time to convert acetaldehyde to ethanol. It can also be a problem with the bottle packaging.

Beer smells rancid

• Odor: Butyrate

• How to identify: This smells rancid, like a sick baby.

• What it is: Butyrate off-flavor is a very distinctive odor that smells like baby vomit. No, it is considered an off-flavor in all beers.

• Cause: Butyrate is produced by bacteria during the wort production stage, but can also be produced by bacteria when beer goes bad after packaging.

Beer Smells Like Vinegar

• Odor: Acetic Acid

• How to Identify: This beer smells like vinegar, sour, or stale beer and can be tasted on the sides of the tongue near the back of the mouth.

• What it is: Acetic acid is a vinegary, or sour, flavor that is present in all beers, but in varying concentrations. It is present in all lagers, ales, stouts, and wheat beers and is a normal component of flavor balance—think lambics that have been exposed to specific types of wild yeasts and bacteria. However, when acetic acid concentrations are too high, it can cause off-flavors in most beers.

• Why it's produced: Acetic acid is produced by yeast during fermentation and is a natural part of the beer-making process. Wild yeasts also produce acetic acid, but they produce more than other yeasts, which can change the flavor of the beer. A sour or vinegary flavor is almost always caused by bacteria or wild yeast infection. Bacteria that consume sugars also produce acetic acid, which is a sign of a spoiled beer or other problem.

Beer Tastes Like Cheese

• Odor: Cheese

• Chemical Name: Isovaleric Acid

• How to Identify: This smells like stale cheese or sweaty socks.

• What is Isovaleric Acid: Isovaleric acid flavor is typical of certain beers, such as India Pale Ales. This typical "cheesy" flavor is usually associated with extremely bitter beers. In pale lagers, isovaleric acid is considered an off-flavor.

• Cause: Isovaleric acid off-flavors are usually produced by aging hops. This compound is produced as hops age, losing their bitter alpha acids, producing a taste similar to cheese, molasses, or grape juice.

Beer smells like mouthwash

• Odor: Chlorophenol

• Chemical name: 2,6-dichlorophenol

• How to identify: This odor smells like mouthwash, Band-Aid, antiseptic, disinfectant, and has medicinal or hospital properties.

• What it is: Chlorophenols are transferred into beer due to external contamination of brewing ingredients or packaging materials - for example, brewing with chlorinated water or flushing equipment that comes into contact with beer.

• Cause: This can be caused by improper flushing during the cleaning phase of the brewery, allowing chlorophenols to enter the beer inventory. This can also happen if the beer conveyor line is not flushed.

Astringent beer

• Odor: Tannin

• How to tell: This beer tastes dry, grainy, opaque, and rich in tannins, like a hygroscopic tea bag or grape skin.

• Astringent: Tastes like powder or metal, and has a wrinkled mouthfeel. Astringency can also taste sour, vinegary, tannic, and dry.

• Cause: Polyphenols and tannins are the primary causes of off-flavors in beer. Tannins are found in the skins or husks of grains and fruit peels. Grains that have been soaked for too long or have been ground or crushed release tannins.