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How many times can I repitch yeast?

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NinjaBob

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Post Thu Nov 18, 2010 2:27 pm

How many times can I repitch yeast?

I've heard that 5-7 times is the max, but why? I've heard both that there's a contamination risk, and that the yeast starts to mutate.

I'm inclined to disbelieve the contamination risk theory, because it seems like the risk would be the same as it would with new yeast fresh from the store.

As far as mutation goes, what should I expect? If it keeps creating tasty homebrew, I don't really mind if it's not the same from batch to batch, but if it becomes an undrinkable abomination, that's another story.

Anyhow, I brewed The Innkeeper (Wyeast 1469 PC West Yorkshire Ale, OG: 1.043), then repitched into Spiced Winter Ale (OG: 1.047), then repitched into Shirley Furioso (OG: 1.062). My plan is to keep repitching for as long as I can (read: I end up with undrinkable or unfermented beer).

The first two times, I just poured the new wort right on to the yeast cake after I racked the previous beer into secondary, and the third time, I saved the yeast cake from the primary in an erlenmeyer flask, and refrigerated for a few days. So far, everything's been going great. I'm considering washing the yeast this next time, since I'm sure the trub has been building up.

Thoughts, suggestions, concerns, advice?
On tap: Fearsome Cider (12.5%), Pumpkin Ale
Primary: empty
Secondary: Synchronicity Wheat, Cider, Wildflower Mead (1 year)
Conical: empty
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sl8w

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Post Thu Nov 18, 2010 3:28 pm

Re: How many times can I repitch yeast?

I've never tested the limits, but after a while the yeast will start to get dusty, won't floc, and fermentation time will slow significantly. I usually stop re-pitching when I'm sick of the yeast, want to try something new, or start seeing signs of slower or stressed fermentation. You may be able to get a few more generations if you top-crop the yeast, as you would likely be getting the healthiest and most active yeasts that way.
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Wahoo

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Post Thu Nov 18, 2010 3:36 pm

Re: How many times can I repitch yeast?

The two things I have seen that have told me it is time to start with a new batch of yeast are either underattenuation or lack of flocculation. I don't think this is genetic mutation as much as it is me inadvertantly selectively harvesting either high or low floculating cells with my harvest and propogation techniques.
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NinjaBob

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Post Thu Nov 18, 2010 3:52 pm

Re: How many times can I repitch yeast?

Well, harvesting from the yeast cake is sure to select the low-flocculating cells, so I'm sure I'll run into a problem eventually, especially if this yeast is supposed to be medium- to high-flocculating.

I guess I'll repitch this yeast two or three more times, and then pick up some new stuff.

At $6.25 for an Activator pack, it's not like yeast is expensive, but if I can reuse the same yeast 5 times, that adds up to $31.25 in savings -- enough to buy enough ingredients for another 5 gallon batch.
On tap: Fearsome Cider (12.5%), Pumpkin Ale
Primary: empty
Secondary: Synchronicity Wheat, Cider, Wildflower Mead (1 year)
Conical: empty
Up next: Caribou Slobber
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a10t2

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Post Thu Nov 18, 2010 7:26 pm

Re: How many times can I repitch yeast?

NinjaBob wrote:Well, harvesting from the yeast cake is sure to select the low-flocculating cells

Not unless you pull exclusively from the top of the cake each time.

I've heard of breweries repitching 20+ times. The big concerns are contamination (there's always *something* other than yeast in there, and with each repitch the density of the baddies increases) and off-flavors due to autolysis. Personally, I probably wouldn't be comfortable with 20 brews, but I'd probably consider going as high as 10. At work, we stop at 5 or when the cytometer sample contains a bacterial cell, whichever comes first.
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NinjaBob

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Post Thu Nov 18, 2010 9:43 pm

Re: How many times can I repitch yeast?

a10t2 wrote:off-flavors due to autolysis


I thought autolysis was a myth...? I've read so much about "Oh no, look out for autolysis!" and an equal amount that's "Don't worry about autolysis -- I leave my beer in the primary for 12 months at a time!"

I, personally, have never had a beer that tastes yeasty, but I almost always rack to a secondary after 2 - 3 weeks; it's mostly just a habit, and recently, a way to free up primary fermenters (and the yeast cake).
On tap: Fearsome Cider (12.5%), Pumpkin Ale
Primary: empty
Secondary: Synchronicity Wheat, Cider, Wildflower Mead (1 year)
Conical: empty
Up next: Caribou Slobber
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The Professor

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Post Fri Nov 19, 2010 12:41 am

Re: How many times can I repitch yeast?

These days I stop after 8 or 9 repitches... but I have certainly gone upwards of 20 in the past. These days I stop at 8 or 9, but I have my house yeast banked and it's easy to start over.

If your sanitation is good and your yeast is robust, there is no reason not to push the limits.

If you keep it all clean right ondown the line, this comes under the heading of "relax, don't worry..."
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a10t2

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Post Fri Nov 19, 2010 8:30 am

Re: How many times can I repitch yeast?

NinjaBob wrote:I thought autolysis was a myth...? I've read so much about "Oh no, look out for autolysis!" and an equal amount that's "Don't worry about autolysis -- I leave my beer in the primary for 12 months at a time!"

IMHO, time isn't much of a factor. I'm more concerned about cell wall damage due to budding. Fix talks about it in Principles of Brewing Science; IIRC, he says the limit is about 20 generations, and you could have individual cells hitting that after only 4-5 repitches. From that point on, the proportion of dead cells only increases.
Beer is like porn. You can buy it, but it's more fun to make your own.
http://seanterrill.com/category/brewing/
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blatz

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Post Fri Nov 19, 2010 8:34 am

Re: How many times can I repitch yeast?

The Professor wrote:These days I stop after 8 or 9 repitches... but I have certainly gone upwards of 20 in the past. These days I stop at 8 or 9, but I have my house yeast banked and it's easy to start over.

If your sanitation is good and your yeast is robust, there is no reason not to push the limits.

If you keep it all clean right ondown the line, this comes under the heading of "relax, don't worry..."


+1 - I've bought yeast <three times in the last 12 months and yet I brew 12 gal every 3-4 weeks...
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blizzardofoz63

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Post Fri Nov 19, 2010 8:48 am

Re: How many times can I repitch yeast?

NinjaBob wrote:I thought autolysis was a myth...? I've read so much about "Oh no, look out for autolysis!" and an equal amount that's "Don't worry about autolysis -- I leave my beer in the primary for 12 months at a time!"


Autolysis is definitly not a myth. I had a beer that I left on the cake for 4 months once sitting at 65F the whole time autolyze. Plasticy, yeasty, rancid flavors described that beer. Luckily, the beer only sat that long because the other half of it wasn't all that great (bad recipe, but drinkable), so I didn't have much of a problem tossing it out.

I have however had beer sit in a fridge for a few months on the yeast cake and that beer was great. There are a few factors that go into autolysis, but it does happen.

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