Fresh Wort on a used yeast cake.

[RobinW]

I kegged a couple of brews this arvo and dropped a new cube of wort onto the yeast cake from one of the brews I just kegged. I've done this a couple of times before without issue.

Question is, how many times can I repeat this before the yeast mutates and produces rubbish?

 

[Nullnvoid]

I can't comment on how many times you can do it as I don't know but you probably don't need the whole yeast cake. Unless it's a massive beer like a RIS you probably only need a couple hundred mls of yeast.

From what little I understand that will have a greater impact than reusing again and again.

 

[Schikitar]

I think you can push it between 6-10 times safely (but that really depends on your setup/cleanliness/strain), you do need to be careful what style you are dropping on what previous style etc., if looking to reduce potential off flavours. With similar OG's you really only need a cup of slurry, if you have a secondary clean fermenter, just scoop out a cup from the other one and drop on top of that..

 

[MrSheen]

I would be less concerned with yeast drift when placing wort directly onto a used yeast cake, and more concerned with the buildup of non yeast sediment, especially if you do significant dry hopping straight into the fermentor.
Also when I do this, I try to keep oxygenation to a minimum as IMO there should already be an adequate amount of yeast from the previous fermentation, so it shouldn't need to undergo another aerobic growth phase. Though i'm keen to hear what others do.

 

[Naboo]

I would only re-use the yeast cake once if pitching straight in on top. Mostly for sanitation issues. I'm not sure how long you could guarantee the fermenter and krausen scum would stay sweet. Personally I'd rather gather some slurry, clean the fermenter and repitch the slurry if reusing the yeast. It may work better dumping it in on top if you've got a big beer going in second though.

Purely hypothetical though as I've never pitched directly into the yeast cake. So take that with a grain of salt I guess.

 

[RobinW]

Cheers for the input.
I always use starters, even for dried yeast, but I've only ever put a new wort cube on top of the 1st iteration.
I'll try for 2nd iteration in about 10 days and see what happens. 6 to 10 iterations is way more than I thought.
Better start drinking to make room

 

[Schikitar]

6 to 10 iterations is way more than I thought.

To be fair, that's more the case if you harvest and wash the yeast..

 

[RobinW]

I'm way to lazy for that caper.

Spending 5 hours brewing is already a bit of a push.

 

[Danscraftbeer]

There are quite a lot of reasons not to pitch onto an uncleaned fermenter with the entire yeast cake. Its grimey with lots of crud and dead yeast too that can cause off flavors plus correct pitch rates have reason. Its about yeast growth and reproduction that goes with viability as well. An entire yeast cake can be up around 6 - 8 times as much yeast that is optimal. The yeast doesnt need to grow or reproduce that takes out a character in flavors too.
Fresh yeast cake you may only need as little as ~60 - 100ml. All depends on your OG.
and clean your fermenter!

 

[Black Devil Dog]

I regularly dump fresh wort on to the yeast cake, but I only do it once. It's not best practice, but it's practical for me and I'm satisfied with the results. I wouldn't do it any more than once though.

 

[Kingy]

The few times ive dumped onto a yeast cake I’ve come home to a Krausen explosion that’s blown the glad wrap off the fermenter.
I used to collect a schooner of slurry to repitch but these days I just add a new packet of yeast. It only adds a few bucks to the total cost of a brew .

 

[Yobbo]

Ive seen a commercial Brewery in Ireland re-pitch over 128 times (Constantly fermenting and same beer)

On a homebrew level, you can easily go over 10 if you are doing similar styles, there are many ways to do it, a cup of slurry is the easiest but not eh best.

Taking 2 cups and rinsing the yeast is also a very good way to go as you are only pitching healthy viable yeast

If you already do starters, freezing samples of yeast in test tubes and freezing them in Glycerine can lead to a large stock of pure strains (and generations of) is by far the best way.

 

[Yuz]

On a homebrew level, you can easily go over 10 if you are doing similar styles, there are many ways to do it, a cup of slurry is the easiest but not eh best.

My W-34/70 is actually W-34/76 I just take away the collect bottle with all the crud, leaving some yeast on the bottom of the 'Saurus. There's minimal risk of infection as everything is under CO2 blanket and enclosed. And, since the yeast is "active" the fermentation starts within two hours - no lag whatsoever.
Six batches is as far as I'd go however, I just like my fermenter clean.

 

[michael_aussie]

I reuse the old yeast cake until I see signs of infection in the krausen line.
I always get 2, usually 3 and occasionally 4 batches from the "first" batch with a good quality yeast (eg Safale US05).
I don't divide the cage, or wash the cake. I just keep everything clean and tip the next wort on top of the old cake.
I've made over 200 batches of beer with only one "off" beer, when I pushed my luck and reused a cake that had signs of infection in the krausen line. A mistake I won't repeat.

 

[shacked]

My W-34/70 is actually W-34/76 I just take away the collect bottle with all the crud, leaving some yeast on the bottom of the 'Saurus. There's minimal risk of infection as everything is under CO2 blanket and enclosed. And, since the yeast is "active" the fermentation starts within two hours - no lag whatsoever.
Six batches is as far as I'd go however, I just like my fermenter clean.

The Co2 blanket is kind of homebrew folklore. Once a container (or fermenter) is open then air mixes in with the Co2. (http://beerandwinejournal.com/can-co2-form-a-blanket/)

 

[keine_ahnung]

I kegged a couple of brews this arvo and dropped a new cube of wort onto the yeast cake from one of the brews I just kegged. I've done this a couple of times before without issue.

Question is, how many times can I repeat this before the yeast mutates and produces rubbish?

Hi Robin,

good question.

In theory, one can keep "re-using" the yeast for ever. Because, it keeps reproducing. Part of the fermentation process is cell-production. A yeast mother-cell can pump out 20-25 new cells - before she's pretty much so old and scarred that you'd prefer to have her out of the way.
The good thing is,you can throw out all these older cells, and use the younger fresher ones for your next brew. (From first hand experience, bavarian breweries will re-use yeast from 10 to x-million times. Because of the whole reproduction effect i just described).
HOWEVER there are a few things you need to be careful of:
1. Hygiene - as always with all things brewing after the boil (Kaltbereich - sorry, my english brew terminoligy is out practice)
2. Once the yeast has digested all available energy sources (i.d. the glucose, maltose and maltotriose in the wort), it'll start looking for other things to digest-----> itself. (Autolyse). This can be largely avoided by cooling it down to below approx. 2*C\
3. In combination with 2. it's important get rid of the old cells and other sediment that falls out of the previous batch during the fermentation.
4. Rapid changes in pressure -> bad for the yeast (but i'm guessing this is irrelevant for you

In the brewery - with the luxury of conical tanks - we let the old yeast and shit out of the bottom of the tank and the end of fermentation and harvest the best yeast, then "rack" into the lager tank. With the harvest yeast, either we pitch it straight away, or store at 1deg until we need it again.

Assuming you have a couple of plastic fermenters, I would recommend harvesting from the top of your yeast cake into the second (clean!) fermenter, then chucking your cube onto that.

Regarding the co2 blanket - I also originally thought that was a good idea (co2 = poor growth conditions for most beer-damaging bacteria). However I remember hearing why that's actually bad for the yeast from another Braumeister a couple of years ago. Can't remember exactly what it was, but can gladly look into it if you're interested