How many times can you use yeast cake?

I have used same yeast cake with my ales 3 times on the fourth batch and no activity in 18 hours. I know its not the way to do it but I enjoy seeing what works and what doesn't. What experiences have all had reusing yeast cakes?

I've only reused twice. Not because I think there is a change for noticeable mutation (Or probably more like selective harvesting) but because I don't usually brew very often and they are usually different beers, calling for different yeasts.

I've heard of brewers using the same batch of yeast 4-5 times, maybe up to 10 before they decide the properties the yeast give the beer are sufficiently different from the original batch to be considered unwanted. I've heard of some breweries using the same strain for decades, but I don't know if that's reusing the same yeast, or simply propagating more batches from the original pitch.

I highly doubt your yeast not showing activity is due to the reuse. Even if some characteristics change over many re-uses, it should still ferment more or less similarly after only 4 uses.

The yeast are just worn out. Using a whole cake will result in little reproduction of new yeast, leaving yeast that are already used up to do the work.

When reusing yeast, use only a quarter to a third of the cake, that way you will have a decent pitch and get plenty of reproduction.

If you like the result and have decent sanitation, yeast can be reused many times; 5, 10, even 20 times. But you will notice changes over time as a result of your brewing practices, temperatures, and selection/handling. Flavors, attenuation, flocculation, etc will change over time.

I have gone 5 rep itches of 1/4 of the yeast cakes with no noticeable flavor changes. That said I have a untrained palate. the yeast was us-05 and bry97.

itsbarleytime said:

What experiences have all had reusing yeast cakes?

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I just use the whole yeast cake once. If I plan to use the yeast more, I try to clean it and if batches are distant in time more than 10 days, I do a starter