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Why would washed yeast 'wear out'?

I’ve been trying to recollect yeast from each batch I do, just to have an ‘on the fly’ yeast library.

The washing part if pretty simple really, and I’m not having any issues there. However, most posts I read say that a washed strain of yeast has about 10 uses before you need to re-buy or once it ‘turns peanut butter color’ you should re-buy.

Where I’m confused is that if you are consistently using the same yeast with the same beer, or similar beer and re-collecting, shouldn’t the yeast get better not worse?

I can understand why, particularly if you were alternating the types of beer you were using it on, it would lose the original character, but if you’re using it on the same beer the same way every time it seems like with that many generations the yeast would become more acclimated to making the beer you want, not less?

Am I missing something?

I think there are millions of generations of yeast that happens during a typical ferment. So the yeast will eventually evolve into something else. That could be good or bad. I think it’s because of the other critters in there. The critter to yeast ratio goes up with each reuse? Maybe if you did an acid wash vs water? All you can do is try . . . and report back what you find. I’ve often wondered what would happen.

I think the “Pros” would say at that point you don’t really know what you have any more and since yeast is such a big contributor to the overall product yet relatively cheap to the overall cost, why would you want to take such a risk and not know 100% what you are pitching?

Of course, you could end up developing your own strain.

I am not a scientist, but I read the Yeast book by Palmer and Zainasheff and somewhere in there it talks about mutations occurring at some point, so you are not pitching the same yeast through many many reuses. I have also heard the guys at Wyeast say that 3 times for a reuse by a homebrewer is the most that they suggest (of course they sell yeast, so it is in their best interests for you to buy the yeast). Finally, I heard something about bud scarring that occurs on yeast if insufficiently cared for- essentially a scar develops on the spot where budding occurred, so it prevents a proper reproduction as the yeast cell goes forward.

Having said all that, I have reused yeast up to five times - that is as far as I want to push it, because I don’t want to risk contamination. I am not as anal in my process as others, nor do I want to do slants for freezing, etc… For me, buying another tube and making a starter is just an easy enough thing to do.



If I can get four or five uses from a yeast I’m happy. I did use one strain for an entire year, in at least six or seven beers.

Seven to ten uses is average for me. My record though, is (I think) roughly 22 successive uses…and I could have gone longer but decided not to press my luck.
And I don’t rinse the yeast…I tried it a few times and found that it made no difference.

22 uses, that 25 cents a pop! Very nice.

I don’t rinse either, I think the best thing for yeast to sit in is beer. Water has low osmotic strength, that would probably stress a yeast as much as alcohol.

I had read somewhere that one of the main reasons to only use yeast X amount of times is it is impossible to keep wild yeast out and will eventually not be the same yeast you started with

Contamination is a possibility but with a healthy yeast culture it usually swamps out the sloweer growing, low cell count competition. But every time you harvest you select for one trait or another and it can change the yeast over time. Plus the stress of fermentation over multiple generations can lead to faster changes. Rather than streak a plate and start with a new colony its a lot easier to just buy another vial/pack.

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