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I heard about some possible errors in the process that cause off-flavours (for example skunk due to sunlight). Excluding infection problems, and talking about most obvious errors one can do and are rather easy to identify and correct, what are the most common off-favours a homebrewer faces, what are the causes and what the soutions?

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This is a broad question, with many possible, valid answers. But rather than close it, I made this a Wiki, since the answers could be useful to brewers troubleshooting off flavors. –  mdma Apr 21 '13 at 23:07

7 Answers 7

Banana and Bubble Gum

Produced intentionally in certain styles (like Hefeweizen), the flavor is reminiscent of banana candy or "Juicy Fruit" bubblegum. The flavor comes from esters produced when (1) fermenting yeast at a higher temp range than optimal, or (b) under-pitching the yeast, or otherwise stressing them out (not enough oxygen, etc).

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Puckering / Tea bag

When the beer has a drying, puckering quality, this is typically due to increased tannins in the beer. There are two main ways tannins can enter the beer:

  1. Fly sparging with water above 5.8pH and temperature above 176°F/70°C, which extracts tannins from the grain husks

  2. Boiling a large quantity of hops for a long time. (e.g. 200g/8oz in a 20l/5gal. batch.)

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Infected roasty beers can take on this flavor as well, as my last Oatmeal Porter can attest :( Was good for a few weeks, then "meah", then chalky and foamy. I think its basically just the roast coming through too strongly since the malt/sweet backbone gets taken out by some rogue Brett or something. –  Graham Apr 22 '13 at 16:59
    
This is a good anecdote, although I feel the acrid dryness of roast is different from the puckering from astringency. It's like burnt toast compared to lemons. How about you add your dry/chalky as a new answer? –  mdma Apr 22 '13 at 17:02
    
I've had flavours that I'd describe this way from having ground my steeping grains wayyyy too much. –  Mark McDonald Apr 24 '13 at 0:42
    
@C4H5As The fineness of the crush won't cause this problem alone. Brew In a Baggers double crush everything into a powder as standard practice. –  Graham Apr 24 '13 at 14:31
    
@Graham interesting - oversteeping then? I was still using a grain bag for what was essentially flour, which would have leaked heavily into the wort. –  Mark McDonald Apr 29 '13 at 8:44

Here's some great info from How to Brew by John Palmer

http://howtobrew.com/section4/chapter21-1.html

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Medicinal / Band-Aid

With a flavor reminiscent of cold medicine, or an almost "rubber"-like twang, this one was very confusing to me when I first found it in my Dark Imperial Blueberry Witbier (as wretched a brew as it sounds).

There are two commonly accepted sources of this flavor: (a) bleach and (b) wild yeasts. The beach you get from not properly rinsing bleach-based cleaners/sanitizers. The wild yeast you can pick up from improper sanitation practices.

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I think Chloramine also a contributing factor for this off-flavor, although I can't speak from experience since it's not used at all in Norway. –  mdma Apr 23 '13 at 18:08

Burnt flavors

When using extracts, if the product is not mixed into your wort properly it can settle on the base of your kettle & get burnt.

Make sure you mix well when adding liquid or dry extract.

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A good rule of thumb when adding extract is to take the kettle off the heat entirely, then pour in the extract, then mix it up really well before returning it to the heat. –  Graham Apr 24 '13 at 14:33
    
@Graham +1 for your excellent advice that was not in my introductory books :) –  Mark McDonald Apr 29 '13 at 8:42
    
Yeah, the bottom of my first brew kettle was routinely covered in a layer of dark brown/black caramel by the end of the boil until I heard about this tip. –  Graham Apr 29 '13 at 12:24

Wet carboard flavour = Oxidized I'm an expert at this one because I had to bottle without using a bottling wand so the beer got oxygenated as it was going into the bottle.

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Soapy, Chemical or Corn flavors

Under pitching yeast can result in as a result of the yeast overworking while eating all the sugar.

Always use a yeast calculator and pitch the proper amounts of yeast.

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