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> Off-aromas in Beer, contributed by sidney porter
MtnBrewer
post Aug 4 2007, 11:14 AM
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This FAQ will help you recognize common off-aromas in beer. The idea is to "doctor" the beer by adding a substance that will alter its aroma and then observe how it smells. This would be a good demonstration to perform at your next club meeting. Best results are obtained when the observer sniffs the reference and then the sample containing the off-aroma contaminant. Note that you aren't supposed to drink the beer (I know it's difficult); you are only supposed to smell it.

Here are a list of common off-aromas and how you can simulate them in beer:
  • Reference sample - no addition.
  • Acetaldehyde - created by yeast, or bacterial infection. Can be acceptable in some styles (American Standard). Sample created from green apple jolly rancher.
  • Acetic - Contamination. Can be acceptable in some styles (lambic, sour brown). Sample created by vinegar.
  • Lactic - Contamination. Can be acceptable in some styles. Can also be created by overly acidifird mash/sparge. Sample created by lactic acid.
  • Cheesy - Created by old poorly stored, oxidized hops. Sample feta cheese.
  • Chlorophenol - Usually caused from poorly rinsing bleach. Sample medical tape*.
  • Diacetyl - Buttery/butterscotch flavors, can be acceptable in some styles (British ales). Created by yeast, some yeast (mostly lager, but also Ringwood ale and Irish stout) require diacetyl rest to remove the diacetyl. A diacetyl rest is accomplished by raising fermentation temps to 60-65F near the end of fermentation. Sample made by butter flavoring.
  • DMS - Dimethyl Sulfide. Vegetal aroma and flavor created but short or weak boil, so cooling. Can be acceptable in some pale lagers. Sample made by canned corn liquid.
  • Phenolic - flavors can vary, from clove, spicy, peppery, to electrical fire. Can be acceptable in some Belgian styles, German hefeweizen. Caused from some yeast strains or bacterial infection. Samples : 8A) diluted honey, 8B) clove, 8C) circuit board*.
  • Skunky - light struck from poor handling, reaction from hops reacting with blue/green UV light. Sample created from leaving the bottle in the sun, 5 hours direct sun light.
  • Solvent - Caused from fusel alcohol produced by yeast fermented at high tempseratures. Sample created from nail polish remover.
  • Nutty - Can be caused by various types of grains. Sample almond extract.
*the medical tape and circuit board were not placed in the beer. I recommend the brown circuit board freshly broken.

Primary sources
Radical Brewing - Mosher
Evaluating Beer - Brewers Publication
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