carbon dioxide

FACTS
passes through yeast cell wall in solution, not as a gas
forms bubbles at nucleation sites such as trub particles and cell-wall exteriors
removes volatile sulfur compounds as bubbles rise to surface
can be present in super-saturated levels at fermentor bottom

CAUSES OF HIGH WORT LEVELS
too little trub in wort
fermentor is under pressure

EFFECTS OF HIGH WORT LEVELS
decreases ester production
inhibits yeast growth
slows rate of fermentation