The staff at The Brew Hut are always happy to try to diagnose any brewing or fermentation issues that you may encounter. You are always welcome to bring a small sample of your beer, wine, cider, or mead to the shop during regular business hours for an expert analysis.

Characteristics Possible Cause Possible Solution
Butter, Butterscotch, Slick mouth feel Diacetyl

Diacetyl is a natural byproduct that is created during the fermentation process by brewers yeast as well as some select bacteria such as pediococcus. As yeast ferment sugars, they typically produce a large amount of diacetyl. As the yeast begin to complete the fermentation process, they will then absorb the diacetyl into their cell walls, thereby reducing it.

  • Always pitch a healthy amount of yeast
  • Allow beer to stay in contact with yeast long enough for diacetyl to be absorbed.
  • Select yeast strain that creates low levels of diacetyl.
  • Ferment at higher temperatures or complete a diacetyl rest.
  • Practice good sanitation.
Cardboard, oxidation, wet paper, sherry Oxidized

Papery flavor in beer is usually caused by the introduction of oxygen which can present itself as wet paper, cardboard or even sherry. Although oxygen is essential for good yeast health, when introduced after primary fermentation, it can quickly deteriorate and stale what would otherwise be a delicious beer.

  • Be very gentle when transferring beer from one vessel to another.
  • Proper head space in fermentation vessels and bottles
  • Use of airlocks to reduce influx of oxygen
  • Serve beer fresh
Corn, Creamed Corn, Cooked Vegetables DMS (Dimethyl Sulfide)

DMS or dimethyl sulfide is most often caused by the use of very pale malts such as Pilsner and 6-Row. During the germination process of barley, a compound called S-methylmethionine (SMM) is naturally produced. In most malts, this compound is driven off during the kilning process. But with lightly kilned malts such as pilsner, the SMM is kilned at lower temperatures and remains in the barley in high quantities. The DMS is then released through evaporation during an open, rolling boil. In cases where the boil vessel is left closed, or in the event that the wort is cooled very slowly the DMS can not be evaporated off and will be reabsorbed in the wort.

  • Use base grains with less DMS precursors such as 2 row malt.
  • When using lightly kilned malts such as pilsner, boil for 90 minutes or longer.
  • Do not cover your boil pot. An open vigorous boil will evaporate a large portion of DMS.
  • Rapidly cool your wort after boiling, to reduce the chance of reabsorption.
Fruity (Banana, Pear, Apple, Strawberry) Estery

Esters are produced during fermentation by both ale and lager yeast.
They can make up a significant part of the characteristic of certain beers, but are generally considered undesirable in high concentrations. Ester production in a beer can be controlled by maintaining healthy fermentations and decreasing yeast stress. Ester production is often enhanced by low oxygen levels, poor yeast pitch rates, brewing high gravity beers, and high fermentation temperatures.

  • Always pitch the appropriate amount of yeast for the beer style and gravity
  • Always pitch the appropriate amount of yeast for the beer style and gravityAerate wort appropriately
  • Aerate wort appropriately
  •  Proper aerationBrew lower gravity beers
  • Brew lower gravity beersFerment at cooler temperatures.
  • Ferment at cooler temperatures.
Green Apples Acetaldehyde

Acetaldehyde is a naturally forming byproduct in beer that is created during the fermentation process when the yeast is converting glucose to ethanol. In the event that the fermentation is poor because of unhealthy yeast, low pitch rate, or if the beer is transferred off of the yeast too early, the conversion of acetaldehyde to alcohol may not be complete, leaving a large amount in the final beer.

  • Pitch the appropriate amount of yeast.
  • Pitch the appropriate amount of yeast.
  • Fully oxygenate wort at pitching.Avoid racking
  • Avoid racking beer off the yeast trub before fermentation is complete.
  • Avoid introducing oxygen into your beer after fermentation.
Metal, Tin like, pennies, blood Metallic

Metallic flavors are most often caused by unprotected metals in contact with the wort,
Iron and aluminum kettles can cause metallic flavors during the boil. Stainless steel pots will not generally contribute any metallic flavors unless over scrubbed. Metallic flavors can also be caused by high iron content in the brewing water as well as the hydrolysis of lipids in malts that are not stored properly.

  • Use stainless steel brewing vessels whenever possible.
  • Ensure that all malt is fresh and stored appropriately.
  • Use water with moderate iron content.
Mouth Puckering Astringency Tannins

Tannins are most often extracted from the malt during the mashing process. If the mashing temperature is too high (over 170 F) or the pH levels of the sparge water is over 5.8. They can also be extracted from the malt when sparging for too long.

  • Don’t mash or sparge with water over 170 F.
  • Keep sparge water below a pH of 5.8
Plastic/ BAND-AID® Chlorophenolic

When a beer is high in phenolics (smoky, spiciness) and is brewed with water that is high in chlorine or chloramines, it can create a plastic flavor and aroma that is often described as Band-Aid® like or medicinal. Be sure to use water that has low chlorine or chloramine content and be sure to properly rinse any chlorine-based sanitizers.

  • Choose a yeast strain that is less prone to spicy phenol production.
  • Pitch sufficient quantities of yeast for the beer that you are making.
  • Proper sanitation of all brewing equipment.
  • Use filtered water with low chlorine or chloramine content.
Skunky, Catty Light Struck

When hops are exposed to ultraviolet rays from the sun or fluorescent lighting, the alpha acids from hops break down and react with the hydrogen sulfide produced by the yeast. This reaction creates mercaptan. Mercaptan is the same chemical that skunks secrete when they spray, which is why the smell of lightstruck beer is so similar to that of a skunk.

  • Package beer using brown bottles to reduce exposure to UV rays. Although this will only block some of the light.
  • Keep beer stored in a dark, temperature stable environment.
Smoky/ Spicy/Clove Phenolic

Most often phenols are derived from the yeast during fermentation. Some strains of yeast are more prolific at creating this spicy characteristic such as hefeweizen style strains and some belgian yeast strains. But even yeast that is not necessary prone to creating these spicy flavors can create phenols when stressed from under pitching or high fermentation temperatures. Other culprits include wild yeast and bacteria which can be controlled by maintaining good sanitation practices.

  • Choose a yeast strain that is less prone to spicy phenol production.
  • Pitch sufficient quantities of yeast for the beer that you are making.
  • Proper sanitation of all brewing equipment.
Sour, Tart, Acidic Bacterial Contamination

Contamination is usually caused by the introduction of a bacteria. As there are many different bacterias that can infect a beer, they often present themselves in different ways. The most common bacterias found in beer are strains of lactobacillus and pediococcus. Both are members of the lactic acid bacteria (LAB) group. This means that they convert sugars into lactic acid.

  • Maintain good sanitation practices
  • Avoid introducing oxygen into the beer after fermentation
  • The flavor can be considered pleasant in sour beers such as lambics, berliner weisse etc.
Sulfer, Rotten Eggs, Burnt matches Hydrogen Sulfide

Hydrogen sulfide is produced naturally by all yeast during fermentation. Lager yeasts tend to create greater sulfur aromas than ale strains. At low levels, it can impart a ‘fresh’ flavor to beers but at high concentrations it becomes an off flavor. CO2 will carry most of the hydrogen sulfide away and so conditioning or lagering after primary fermentation can ensure any left-over sulfur smells or tastes fade over time.

  • Select yeast that creates low levels of Hydrogen Sulfide.
  • Ale yeast produce less H2S than Lager yeast
  • Ensure vigorous and complete fermentation
Vinegar Like, Acidic Acetic Acid

Acetic Acid is produced by yeast in fermentation and is a natural byproduct of metabolism during the brewing process. But it can also be imparted by wild yeasts and bacteria such as Acetobacter (vinegar bacteria), a genus of aerobic bacteria that can turn ethanol into acetic acid during fermentation if excessively aerated.
In Lambic and Flanders Red style beers, acetic acid can be a desirable component that adds to the complexity of the flavor and aroma profile.

  • Always pitch the appropriate amount of yeast for the beer style and gravity
  • Aerate wort appropriatelyPractice proper sanitation
  • Practice proper sanitationFerment at cooler temperatures.
  • Ferment at cooler temperatures.