Yeast Autolysis (1)
Autolysis is the process of self-digestion of the body content of a cell bits own enzymes. The slow disintegration and breakdown of the membrane of yeast cells, in the fermentation medium, allows for the passage of nitrogen into the beer, mead or wine. As the yeast cell dies, it ruptures, releasing several off flavors into the product including sulfur and rubber.
With a large yeast mass on the bottom of the fermenter, you have a high potential for off-flavors due to autolysis. Light autolysis will result in a yeasty or brothy aroma or flavor. Moderate autolysis will have a meaty aroma or flavor much like the smell of a bottle of Vitamin B. A product with high autolysis will have a rubbery aroma and flavor and will be virtually undrinkable.
Luckily the propensity of yeast to autolyze is decreased by decrease in activity and yeast mass. What this means to winemakers is rack off the heavy sediment when the specific gravity reaches 1.010-1.020 and again in three weeks to get the wine off the dead yeast. Brewers should rack off the yeast in two to three weeks and bottle or condition in a secondary lowering the temperature for long cold storage with little risk of autolysis.