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Top 10 reasons for yeast autolysis

Autolysis is break-up of yeast cell “on its own”. Deficiency of nutrients, high temperature and alkaline condition enhance autolysis. If yeast is left to fully fermented beer for too long time they will autolysis and make beer off-flavor because of when a yeast cell dies, it ruptures – releasing several off-flavors into the beer.
The autolysis mechanism is the action of disulphide reductase- enzyme can “open” the structure of some cell wall proteins and therefore weaken the wall.

Top 10 reasons for yeast autolysis:
1. Too long storage time before re-pitching.
2. Too high temperature during cold storage
3. Nitrogen starvation.
4. Vitamin and mineral deficiencies.
5. Oxygen deficiencies.
6. Too high carbon dioxide gas in yeast storage tank
7. Too high alcohol in yeast slurry (ethanol toxicity)
8. Too high gravity wort
9. Too high yeast storage tank or fermenter top pressure
10. Too low pH

How to prevent yeast autolysis?
1. Keep yeast short as short possible before re-pitching, normally not more than 3 days.
2. Optimize yeast storage temperature, for my opinion keep yeast at 3 oC is good for yeast healthy.
3. Top pressure yeast storage tank with sterile air not carbon dioxide to keep yeast fresh and healthy.
4. Minimize pressure on top yeast tank as low as possible, lower than 0.5 bars is good for yeast.
5. Re-propagated yeast every 5 generation used.

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