Common Yeast Issues

Here are a few common flavors often present in beer after fermentation, with causes and solutions
Compound

Esters

Character

Fruty, solvent-like, or floral


Causes

low pitching rate, low aeration, high fermentation temps

Solutions

pitch enough yeast and keep fermentation temps low


Higher Alcohols
Spicy, fruity, wine-like
low pitching rate, high gravity worts, high fermentation temps

pitch enough yeast and keep fermentation temps low

Diacetyl
butter
yeast removed dorment before diacetyl absorbed
keep the beer warm for two days following fermentation

Acetaldehyde

green apple
beer roused during fermentation, short aging period

properly age the beer
Sulfur
rotten eggs
excessive yeast growth or inadequate venting during secondary fermentation
pitch enough yeast, monitor fermentation temps, use separate cold break before fermenation, use carboy airlock or bleed the pressure in soda keg