Canabolistic Fermenter (When it all goes wrong)

Nobody likes to go hungry not even your yeast. As long as their happy their making large amounts of alcohol to make you happy. If there is no available sugar, they turn on each other. When a yeast eats a sugar molecule, it converts to alcohol, but when it eats another yeast, it converts to toxins and will release a powerful oder and poor taste into the wine. Under less then ideal conditions the canabolism can run ramped. One condition that seems to happen a lot is when making dry wines. When the tolerance level of the yeast isn't reached before the sugar runs out, high concentrations of yeast are forced to turn on each other polluting the wine. When the tolerance level is reached before the sugar runs out, the yeast die from alcohol but the ones still alive have sugar to eat. If making a sweet wine, sorbate can be used to stop the last of it without the problems of canabolism.

There are varying degrees of this condition. It may not be noticeable, or it could smell like a sewer. It's just one of those things everyone needs to be aware of.

Yeast are not cannibals. They do not turn on each other, they go dormant when left without food.

Autolysis refers to the destructive enzyme that is released from the cell itself. The toxin released from a dead cell is harmful to live yeast but since very few yeast (relative to numbers) actually die, it's not much of a problem.

I really wonder how often poor sanitization is confused for autolysis. I imagine infections occur more often autolysis. I don't know a single person who has had a bonifided case of autolysis. It seems like a 1970s or 80s homebrewing myth, combined with somebody with an ego too big to admit they had an infection.

Yeast are definitely not "canabols". And potassium sorbate really just renders the yeast incapable of multiplying (which they usually do by "budding" or splitting). The reason why sorbate stops the fermentation process is because without reproducing, those parent cells die off without producing offspring to continue the process.

And autolysis, if it can even be considered a problem for homebrewers, is a very rare occurrence where a dead yeast cell is "digested" by its own enzymes. Like Schlenkeria, I've never heard of anyone who has had a problem with autolysis that couldn't be explained by bad infection or mishandling of the beer.

Also, I'm not really sure that reaching the alcohol tolerance of a yeast will actually kill it. I always assumed that it just rendered the yeast incapable of eating any more of the sugars because of the ratio of alcohol to sugars or water or something. But don't quote me on that.

We wash yeast with alcohol. I'm pretty sure alcohol won't kill them, just cause them to go dormant.

Osmosis will kill them, though, so if they are left in a non-ideal osmotic solution they will die. Freezing solid also seems to kill them dead... I'm running an experiment now with my eisbock, seeing if it will carbonate without any yeast added back in after the freeze concentration.

Yeast will eat dead yeast... and some yeast will kill other yeast... but as for "toxic" chemicals being released, I dunno.

If you rack your wine off of the lees whenever you have lees 1/4" thick every 60 days or so, you won't have any autolysis issues. There are some wines that benefit from staying on the lees, as long as the lees are stirred. I always rack off of the lees, though, since I like a "cleaner" taste.

From Jack Keller's website:

Autolysis:
The decomposition of dead yeast cells that can be favorable or unfavorable, depending on the wine, the yeast, and the process involved. The favorable process can occur in wines that are aged sur lie ("on the lees"). Certain wines such as chardonnay or sauvignon blanc benefit from autolysis because they gain complexity during the process that enhances their structure and mouthfeel, give them extra body, and increase their aromatic complexity. Aging sur lie is usually done with an accompanying regime of periodic lees stirring that can result in a creamy, viscous mouthfeel. See Lees and Sur Lie Aging.



It doesn't matter whether you are fermenting a sweet wine or a dry wine, and sorbate doesn't help. Sorbate simply keeps yeast from reproducing, not fron autolyzing. Too much time in contact with the lees is the cause.