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What off Flavors are Making Your Draft Beer Taste Bad? (and How to Fix Them)

Beer tastes better coming from a draft system, this is the general consensus that most of the general public hold. However, in some locations, the beer just doesn’t taste the same; in fact, the beer tastes bad. It might be a subtle difference in flavor but a beer aficionado, or a person dedicated to a single brand, will notice the difference. The repercussions of this are often subtle, as the general public on the whole is quite uneducated on the off flavors in beer. That makes it even more important that owners and operators take care of their draft systems. After discussing beer off flavors in draft systems, and how to resolve them, we’ll quickly touch on off flavors in bottled beers (light struck) as well as some off flavors which can arrive in the keg from the brewery.

Draft Beer Off Flavors

  1. Buttery (Diacetyl)

Type: Aroma and Flavor

Flavors:  Buttery, butter theater popcorn. In large amounts, butterscotch

Cause: Bacterial contamination of draft lines 


  1. Vinegary (Acetic Acid)

Type: Aroma and Flavor

Flavors: Vinegar and pickle aromas. Sour vinegar taste

Cause: Bacterial contamination of draft line

            Note: Sometimes a desirable characteristic in lambic and other sour beers


  1. Sour milk/Yogurt (Lactic Acid)

Type: Aroma

Flavors: Yogurt or buttermilk. Sour

Cause: Often heavy, bacterial contamination of draft lines 

Fixing Draft Beer off Flavors

These are the three distinctive off flavors that are the fault of dirty line. To keep draft beer pouring great you should clean your lines at least every two weeks with a caustic chemical cleaning solution using an electric re-circulation pump and then flush them with clean water. Get yourself a copy of the Brewers Association Draft Beer Quality Manual. [Link to our article on this]

Bottles Beer Off Flavor

  1. Skunky/Lightstruck (Methyl/Isopentyl Mercaptan)

Type: Aroma

Flavors: Skunky and rubbery

Causes: The reaction of hop bittering compounds to blue light. Can happen within seconds. 

Fixing Bottled Beer off Flavors

To stop this process beer should be stored in opaque containers i.e. kegs or cans. Brown glass blocks most light, but not all, and green and clear glass block next to none.  Of course, this is all up to the beer producer and there’s very little retailers can do about it. Some large beer brands that use clear and green glass actually rely on this process to give this flavor to their beers because consumers expect it. A way brewers can avoid this happening is by using specific hop extracts instead of hops themselves.

Other Beer Off Flavors

Here’s a list of common off flavors found in beers and their source

  1. DMS (Dimethyl Sulfide)

Type: Aroma

Favors: Creamed Corn, Cabbage, Vegetal. In darker beers smells like tomato juice

Cause: Produced by lightly malted grain in boil. Can signal brew house problems.


  1. Oxidation (Trans-2 Nonenal)

Type: Aroma and Flavor

Flavors: Paper, stale, cardboard, wet cardboard

Cause: Stale beer or beer stored at high temperatures for a prolonged period, more than a couple of days. Also a symptom of over boiling.


  1. Acetaldehyde

Type: Aroma

Flavors: Green apple, apple skin, green leaves

Causes: Too short a fermentation time or too low a fermentation temperature. Under-active or unhealthy yeast


  1. Cheesy (Isovaleric Acid)

Type: Aroma

Flavors: Stinky Cheese, Stinky Feet

Cause: One of many aromas of bacterial infection in beer


  1. Autolysis

Type: Aroma and Flavor

Flavors: Soy sauce, muddy, marmite, umami

Causes: Death of yeast cells succumbing to the stresses of fermentation

Note: Can be a desirable characteristic in older, stronger beers

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