I came across the following on the homebrewtalk forum, and thought it worth posting here as a reference guide in case I need it....
If your beer smells like… The term is…. The source may be….
Adhesive bandages (phenolic)
Bacterial contamination; residue from a sanitizing agent ( this odor is expected of certain style beers)
Apple cider (Acetaldehyde)
Refined sugar in the recipe or bacterial contamination
Baby diapers (Enteric)
Bacterial contamination
Banana (Banana esters)
Certain ale yeast strains, particularly Bavarian Weizenbier and Belgium Strong Ales
Barnyard (Enteric)
Bacteria contamination
Bubblegum (Bubblegum)
Certain Ale yeast strains, particularly Belgium Strong Ales and Bavarian Weizenbier
Butter/Butterscotch (Diacetyl)
Bacteria, certain yeast strains, warm fermentation, short aging
Cardboard or paper (Oxidized)
Contact with air; old, stale beer
Cauliflower or cooked cabbage (Vegetal)
Bacteria contamination
Cloves (Phenolic)
Certain yeast strains; such as those in Bavarian Weizenbier
Cooked corn (DMS (dimethyl sulfide))
Poor grain quality; bacterial contamination
Cooking sherry (Oxidized)
Contact with air; long and warm fermentation
Green Apple (Acetaldehyde)
Refined sugar in the recipe; bacterial contamination
Leather (Oxidized)
Contact with air and/or old, stale beer
Marker (Phenolic)
Bacterial contamination; residue of sanitizing agent
Matches (burnt) or Sulfur (Hydrogen sulfide)
Natural by product of fermentation that’s normally flushed out with the production of carbon diaoxide
Mold (Moldy)
Sanitation problem; leeking package seal
Nail polish remover (Solvent like)
Esters produced during high temperature fermentation
Olives (green or black) or Pickles (Acetic)
Acetobacteria contamination
Paint thinner (Solvent like)
Fusel alcohols produced during high temperature fermentation
Rotten eggs (Hydrogen sulfide)
Yeast autolysis
Rubber (Hydrogen sulfide)
Yeast autolysis
Skunk (Light struck)
Damage from light
Smoke (Phenolic)
Use of dark or smoked grains that evoke this aroma
Soap (Soapy)
Residue from sanitizing agents
Vinyl upholstery (Phenolic)
Bacterial contamination; residue from sanitizing agents
Wet dog (Musty)
Bacterial contamination; lengthy aging of bottle conditioned beer
If you beer tastes odd
Blood (Metallic)
Iron in water supply
Butter/butterscotch (Diacetyl)
Certain yeast strains, warm fermentation
Chalk (Astringent)
Overfermentation; misuse of grain
Harsh (Astringent)
High hop bitterness; misuse of grain
Powdery (Astringent)
Lack of sweetness; grain astringency
Salt (Salty)
Use of brewing salts especially sodium chloride and magnesium sulfate
Sour milk (Lactic)
Lactic fermentation (which is intentional in some beer styles such as Berliner Weisse)
Tin can (Metallic)
Iron in water supply; contact with metals
