Re-using a yeast cake from a bad batch

[MrHadack]

My fermentation fridge went dead on me, and subsequently I had a batch of beer using WLP011 get up to 80F for a few days. It has some pretty bad off-flavors as a result. I need to re-brew this same recipe since it is for a party coming up. I have used existing yeast cakes in the past, but never when there was a bad batch. What I'd like to do is brew the new batch of beer, and once it is cooled, siphon the bad batch out of the fermenter and add the new batch on top of the existing yeast cake.

What I am not sure of is whether or not the higher fermentation temps from the bad batch damaged the yeast in any way. Can I re-use it without fear? Should I chuck the entire thing and make a new starter?

 

[guazzabuglio]

I would pitch fresh yeast. I'm sure the yeast has been stressed enough to throw off some undesirable flavors if you rack onto the same cake.

 

[dinnerstick]

there's nothing inherently stressful about yeast grown at warm temps, i doubt most people grow their starters at fermentation temps, i sure don't, and they can be in the high 20's C and full of weird yeast-derived aromatics. anyways the standard lab temp for propagation of saccharomyces is 28-30 C. you could compromise, as using the entire yeast cake is pretty excessive, by harvesting some of that yeast, growing it up in a small starter to confirm its viability (estimate cell count by an online calculator), and going forward with that new pitch, that way you pitch a reasonable amount, are confident the little buggers are happy, and totally dilute any off flavors, if you're afraid of bringing those along to the next batch (i wouldn't be...). well that's my suggestion anyways, good luck

 

[podz]

My fermentation fridge went dead on me, and subsequently I had a batch of beer using WLP011 get up to 80F for a few days. It has some pretty bad off-flavors as a result.

Can you describe the off-flavors?

What are you going to do with the batch?

I'd certainly reuse the yeast, no question about it. Good advice from dinnerstick, though about taking a small amount and using it to make a starter. Reusing the entire cake would surely bring liquid that contains the "pretty bad off-flavors".

 

[eadavis80]

Though I've never harvested yeast myself, I plan to and have read a lot about it. I read either on WYeast or White Labs websites that you should NOT harvest yeast from batches of beer that have off flavors as the yeast is likely stressed. However, they are in the business of selling yeast and would probably rather have you spend $7-8 for a new pack. That being said, is it worth it to risk a bad batch to save that money? I'd pitch new.

 

[MrHadack]

Can you describe the off-flavors?

What are you going to do with the batch?

I'd certainly reuse the yeast, no question about it. Good advice from dinnerstick, though about taking a small amount and using it to make a starter. Reusing the entire cake would surely bring liquid that contains the "pretty bad off-flavors".

The off-flavors are mostly estery and some sourness. It's not hot; I don't detect fusels, really. Aside from these flavors it attenuated way too low. It was supposed to have a FG of 1.014 and it ended under 1.010. It's pretty thin and dry.

My wife isn't much of a beer drinker, so she makes a great test subject. She has a pretty wide threshold of what she considers good. For example, if something has some minor flaws, and I have her taste it, she will still say "It's fine... I don't know what you're worried about." But this was the only beer in a very long time that caused her to say, "Umm... I think there's something wrong with this one." So there's no way I can give it to people who know what they're tasting! I'm most likely going to dump it.

So I guess what I will do is salvage some of the yeast, make a starter with it as suggested, and then re-brew the batch.

 

[ericbw]

Does high temp really "stress" yeast, or make it really happy?

 

[podz]

I'm most likely going to dump it.

There are a whole lot of folks here who are under the opinion that you never dump a batch and it will generally improve with some aging. Might be the case with your batch as well.

 

[eadavis80]

That's a good point - I wouldn't dump the batch, but I would NOT use the yeast from a batch I'm iffy on for a future batch.

 

[MrHadack]

Okay, so why not make this a learning experience. Here's what I will do:

• I won't dump the batch. I have plenty of fermentation buckets to use. I'll age this one out and report back what happens to the flavors over time. I'll keep copious notes about ambient temps, etc.
  
• I need to make sure the new batch turns out well because I am trying to get it done in time for a party. So I will use FRESH yeast.
  
• However, instead of 5 gallons as planned, I will brew an extra 2.5 gallons. I'll ferment 5 with the fresh yeast and a 2.5 mini batch with a starter created from the old yeast.

That should tell us if the old yeast works as well as the new yeast and we'll know for future reference.

 

[Owly055]

Personally I would have zero concern about this yeast..... it's still the same yeast, and isn't going to produce off flavors in the new batch. It hasn't evolved into something else. It's the fermentation temperature that makes it produce the off flavors......... You aren't planning on doing the same thing again are you??

H.W.

 

[MrHadack]

It hasn't evolved into something else. It's the fermentation temperature that makes it produce the off flavors

This was my thinking as well, but then I thought I'd post the question here just for the heck of it. I still plan to do what I just mentioned above, doing a split batch with fresh yeast and this old yeast just for kicks and see what comes of it.

 

[cjgenever]

Yeast LOVE 80°f. but not for more than a few days without food. You should rinse it rather than pitch slurry. Some flavors have a very low flavor threshold and could transfer over.

 

[Cyclman]

I would do a starter. Energize the healthy yeast with O2 and yeast nutrient, get the dead yeast out by washing them out.

The healthy yeast will survive and thrive, I would want to get any stressed / dead ones out, though.

 

[nh_homebrew]

I am curious what the outcome was for you.

 

[IslandLizard]

The only thing that would deter me from re-using the old yeast cake is the sour notes you're tasting. Hot fermentation should not cause sourness, but I would expect fusel alcohols and estery byproducts to be present, largely dependent on the yeast strain and when temps went out of control.