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I've seen around here and in other sources that for homebrewers a secondary fermentation (concerning autolysis) isn't necessary, unless you're going to dry hoppy or something like that. My question is about autolysis when reusing yeast. When one storage an used yeast for several months, or over several batches, is it needed to be careful with autolysis?

Generally people says that a starter would be enough to get the right amount of live cells and therefore autolysis isn't a problem. But dead cells will survive through starters, why this is not a problem?

For how much time and how much batches is it safe to maintain the yeast cake?

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You'll want to keep the yeast cool (under some beer) or cold (in the fridge after the beer is removed) to minimize autolysis. The warmer it is the faster they run out of glycogen, and once they run out they'll start dying.

Dead cells aren't necessarily a problem, as long as your viability hasn't dropped too much. If most of the yeast are alive, then they will happily eat what's left of the dead ones after they get some sugar and oxygen. However, too much dead yeast is a problem because it means all the other yeast are very stressed. They might not perform as advertised when used again.

Pro brewers usually use yeast 8 to 10 times before they have problems. The problems are usually related to yeast health, but contamination is also a good reason to get fresh yeast from the lab.

Keep in mind that pros are probably storing the yeast only a few days between uses. Maybe someone else can say how long and how many times they get away with at home (no clear answer here). But few serious home brewers do this.

  • first of all thanks for you answer. When you say "too much dead yeast", what is the reference frame? Is it too much when comparable with the alive yeast? Because if so (and if I understood it correctly), we can always perform a starter to increase the viability and, therefore, autolysis will never be a problem and then the only concern will be contamination. – Mr. K May 4 '15 at 14:31
  • You'd this info would be easy to find, even with the Yeast book (White & Zainasheff) sitting next to me...it took Google to find where that book says: "Ideally, you do not want to pitch yeast that has dropped below 90 percent viability." That being said, the yeast would have to be very fresh, and there are plenty of examples of people measuring viability to adjust cell count when the viability is much lower than 90%. – Pepi May 6 '15 at 10:13
  • I think you didn't understand me. Viability isn't a problem, because I can always perform a starter, right? What I'm trying to understand is that, even if there are too much dead yeast (too low viability), autolysis won't be a problem at all. If this is the case, to improve viability is just a matter of making a starter. – Mr. K May 6 '15 at 11:58
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    The stress associated with loss of viability comes with other problems - mutations that affect flavor, or the common 'petite' respiratory mutants that can affect the health of the whole culture. But it gets kind of off topic to discuss all that. I'm just saying that autolysis is a sign other potential problems. – Pepi May 7 '15 at 8:48
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Autolysis is not going to be an issue, but viability will be.

In my experience, viability is very hit and miss. I've stored yeast in canning jars in my fridge for 6 months and they still worked, and I've had some that were very slow to get going and some that didn't work at all that were only stored a month.

Really, I don't harvest yeast much anymore. The time, effort and cost that went in to the rest of the brew isn't worth saving a few dollars. In some cases, the flavor profile will not be the same as the original. It's also near impossible to tell how much yeast you are actually storing. Trub has so much non-yeast material in varying degrees, unless you use a microscope and actually count the cells, you really don't know how much you are working with.

On the other hand, it's kind of fun and interesting and you may want to develop a "house" strain.

Ideally, you should probably limit the storage to a few weeks and make a starter at least a week before you brew, in case it takes off slow. You should be able to build up enough yeast in that time and if it goes quickly, you can decant off the starter and put it in your fridge for a couple of days. If you have a backup yeast and use a starter, you'll be able to control the process and not risk your beer.

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