A Few other Specific Issues
This is a list of a few other issues that home brewers may encounter and can fix. i will add things here on occasion when they strike me as important.
1) Soapy flavors: This will remind the taster of a bar of Ivory soap. It comes from left over fatty acids in the cold break trub, that wind up in the fermenter. Combine this with a warm fermentation, and ugh!
Solution: a quick cooling after a whirlpool to allow all things to settle to the bottom. Trub, hops, and proteins will settle out if left undisturbed during the cooling process, then utilizing a siphon to remove the chilled wort from the brew kettle will leave all the sediment behind. See the Siphon Starter on the Brewing-Beginner Tips page. I find it is simple and easy to use and have been using it for years now.
2) Band Aid-Chlorophenolics. Be sure that brewing water is free of chlorine. Drinking water usually has at least a small trace of chlorine present, which can be removed with boiling. Chloromines on the other hand need to be filtered, or a campden tablet will also pull out the chloromine. Rinse chlorine sanitized equipment thoroughly with hot water. As the Papazian book says, some assumptions must be made when brewing, and hot water off the tap being sanitary is one of them. I have never had an issue with hot tap water in 20 years of brewing.
Just a side note, because the water that I use is high in solids (calcium chloride, etc), I use one half tap water and add one half distilled water to it. This allows me to boil the tap water, then use the bottled water to cool it down then adjust the water to the desired temperature for mash in and sparging. Pre-boiling the day before will also insure that the chlorine has been removed.
Band aid can also come from wild yeast strains. These baddies are most present in the air during the Summer, so keep the brew kettle covered as best as possible during the wort chill. If using an aerating stone, make sure the filter is 0.5 micros or tighter.
3) Apples! Acetaldehyde is a byproduct of fermentation that gives beer a green apple-like flavor and aroma. Usually this will be absorbed with a little age in the presence of yeast. Keeping beer at a stable temperature while fermenting will help reduce production of this compound. Green apple flavors and aroma can also be associated with a cidery character which is caused by using too much refined sugar in a beer recipe. It is best to eliminate table sugar from recipes and substitute malt extract, or even honey. There is also a trace of cidery flavor present in beers bottled with corn sugar, so I would advise using malt extract for priming batches of beer.