How many times can you use the same yeast cake

For the past three batches I have done I pitched onto a washed yeast cake of wlp001. None of the beers were very hoppy and the last one had a SG of 1058. My question is how long do you use the same yeast? In order to keep using it should I wash it and start spliting it up and saving it or at a certain point is it just done and time to buy new yeast?

4-5 generations is the general rule that I've heard, but if you wash your yeast and split it up, 4-5 generations could last you dozens of batches. Chris White from White Labs says you shouldn't store washed yeast for more than a month though, after that the viability has been severely decreased. So if you brew often enough so the yeast doesn't stay dormant for too long it will last a long time.

I have successfully used yeast that has been stored for about 3 months though, and with a good starter is fermented just fine.

Lots of HBT folks say five generations is the safe maximum for reusing yeast before they start to mutate. Washing is better than pitching directly on a cake, as you get rid of most of the proteins, dead cells, etc that are found in the cake. Plus, instead of getting five beers out of one vial of yeast, when you wash you can get dozens.

EDIT: BarleyWater beat me... promise I wasn't plagiarizing!

BarleyWater said:

Chris White from White Labs says you shouldn't store washed yeast for more than a month though, after that the viability has been severely decreased.

I have successfully used yeast that has been stored for about 3 months though, and with a good starter is fermented just fine.

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This is very odd because really what is different from White labs vials and our own washed yeast? One generation. That is all. So our washed yeast really has the exact same "best by" date length as a vial of WL yeast. 4 months. Longer in reality because my pint jars contain a minimun of 4 times the cell count of the WL vials.

Makes sense that he would say that though. Yeast washers are WLs biggest enemy.

dontman said:

This is very odd because really what is different from White labs vials and our own washed yeast? One generation. That is all. So our washed yeast really has the exact same "best by" date length as a vial of WL yeast. 4 months. Longer in reality because my pint jars contain a minimun of 4 times the cell count of the WL vials.

Makes sense that he would say that though. Yeast washers are WLs biggest enemy.

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Washing yeasts at home is not nearly as sanitary a process as in a laboratory situation like at White Labs. It is unlikely that there will be zero contamination, and we aren't storing the yeast in the same medium as it is in the vials. We essentially store yeast in very dilute beer which causes more stress on the yeast we wash than the yeast in a tube. We are also reusing yeast that has just been through the stress of fermenting a beer, which yeast in the vial has not. So actually, there are a number of differences between WL vials and our own washed yeast.

He actually fully explained how to wash yeast at home on a homebrewing podcast, and given that homebrewers are like 1% of White Labs sales, I don't think he's too worried about it.

I'll give in on this. My point was more a statement against his stated shelflife. His expertise notwithstanding 1 month is erring too much on the side of caution. Like you said before you've used it at three months. On my side I pretty much only use it at between 3 and 5 months. I just don't get back around to a yeast for that period of time and I have never had a problem.

The funny thing is that I have used 3 month old washed WL yeast and it performed better than the original vial. No starter on either.

BarleyWater said:

Chris White from White Labs says you shouldn't store washed yeast for more than a month though, after that the viability has been severely decreased. So if you brew often enough so the yeast doesn't stay dormant for too long it will last a long time.

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Well, then the three batches I have currently going, all with washed yeast around a year old, shouldn't be doing anything at all, yet they are chugging along nicely and appear to be quite happy.

Of course he's going to say that. He's got a product to sell, and if you are washing yeast, you are not giving him your money for yeast. Hmmmmm.......

You don't know for sure if your stored yeast is any good until you pitch it into a starter. If you make a starter with it and it is no good, you're only out a couple bucks.

I used a 6 month old washed yeast and it was fine. I did have a packet of dry yeast ready though.

Yesterday in a split 10 gallon batch of APA I pitched a hydrated pack of US-05 in to one half and about 1/2 cup Nottingham slurry that was over a month old in the other. The Nottingham took off faster and is going stronger. Mr. Malty says I underpitched the slurry. The viability calculations must be worst case scenarios.

If it was really old I'd just pitch a little bit into a starter to make a new more healthy generation.

I've heard of people who are very meticulous about the sterilization process washing yeast and using it for dozens of generations. It's just a manner of that small percentage of baddies getting in there grows each time you handle the yeast. Me, I'm not so perfectly sanitary and won't go beyond a couple generations unless maybe I get ahold of a yeast strain that's hard to find.