What is a yeast off-flavor and how do I prevent them?

Answer 1

Yeast off flavors can very widely. The most common off flavors are a burnt rubber flavor from beer sitting on the yeast too long in the primary fermenter or a green apple flavor from too high of a fermentation temperature which can also produce excessive esters that have solvent like flavor, but there are too many others to list.
The best way to avoid yeast off flavors is to ferment your beer at the yeast manufactures recommended temperature. Another way to help eliminate yeast off flavors is to rack/transfer your beer into a secondary fermenter after your primary fermentation has slowed to approximately one bubble/burp per minute coming out of your air lock.