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You are here: Home --> Forum Home --> Brewing Forum --> Recipe Discussion --> How much yeast cake for high gravity lager?

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Catman_bru
SE, WI
7 Posts


I currently have 3.5 gallons of 1.050 lager fermenting with Francoinian dark lager. I should be ready to rack by Sunday/Monday, and I am toying with the idea of using the yeast cake for 3.5 gallons of 1.106 grav dark lager.

Homebrewdad's yeast calculator says I will need just shy of 500bil cells. How much of the yeast cake should I use?




Posted 34 days ago.

mchrispen
Bastrop, TX
485 Posts


Some numbers (take these with a grain of salt) based on my yeast counts:

You should have around 100-150 ml of "thick slurry" after all of the solids have settled for a 3.5 gallon batch. 5 gallons will yield between 150-230 ml of "thick slurry" and the amount will vary based on gravity and volume of the host beer, as well as the yeast strain. By thick slurry, I mean the result of a starter (or harvest) cold crashed for 48 hours in a fridge... and the supernatant decanted leaving just a thin finger of clear beer above the cake. Freshly harvested yeast - in a thick slurry - should generally be between 1B-1.2B cells per ml, but extremely fresh and viable coming from a moderate to low gravity beer.

100 ml @ 1B cells = 100B cells as a reference. So for 500B, you would need 500 ml of slurry... much more than you likely have, using the minimum numbers in the exercise.

I would harvest the whole cake and cold crash it to determine how much yeast you may have and work out the math from there using the minimum numbers - and make an appropriate starter. It is hard to overpitch a high gravity lager. Advantage is viable and fresh yeast, disadvantage is a lot of osmotic pressure from the super high gravity of your second beer. Too many unknowns. Hard to be more specific.

Or, pitch on the cake and be patient as this will take a good long time to ferment cleanly at traditional temperatures.

Others might disagree with the above :) YMMV




Posted 34 days ago.
Edited 34 days ago by mchrispen

homebrewdad
Charter Member
Birmingham, AL
2480 Posts


I was hoping that mchrispen would respond.  I just don't have the experience with reusing the cake to feel comfortable in responding.



Posted 34 days ago.

chino_brews
Charter Member
Eden Prairie, MN
301 Posts


If you plug your first lager into a yeast calculator as if it were a 13.3L non-stirred starter, then you end up with 822B yeast cells. Your HG lager needs 498B cells. So you could leave an inch of beer on the yeast cake, swirl it up, give it a few minutes to allow sediment to settle (most yeast will stay suspended), and pour off the liquid yeast. You could allow this to settle more or cold crash. Then use 2/3 of either the thick slurry after decanting the supernatant beer, or you could mix it up and just pour in 2/3 of the harvested yeast/beer. The first yeast handling step is best done at room temp to discourage flocculation before the sediment settles.



Posted 34 days ago.
Edited 34 days ago by chino_brews

Catman_bru
SE, WI
7 Posts


In my assumptions I followed chino's logic, but I cant seem to poke any holes in mchrispen's numbers. Considering how difficult high gravity brews can be, I think I will play it safe and build a starter from harvested yeast. 

Thanks for the advice!




Posted 34 days ago.

mchrispen
Bastrop, TX
485 Posts


You know, Chino's approach would probably work fine. I believe (but don't have any proof) that starter modeling isn't linear above certain volumes. Of course, the usual rules apply to gravity, etc. There are limits on yeast cell growth - generally a 4 liter starter limits growth to ~400-450B cells, but the potential of wort at 1.040 at 4 liters is much higher... the damned crabtree effect is the limiter and thus the need for stepped starters. I am pulling about 0.5 liter of "thick slurry" healthy yeast from my conicals with 11-12 gallon batches, more if it is a true top cropper and I harvest yeast twice during krausen. Of course, I am leaving a lot of it behind to clean things up. I have never really harvested from a bucket or carboy fermenter (save the repitching on cake technique). I am guessing the fermenter geometry may have some play here, as the slurry from my carboys seemed much less dense, even after a cold crash. I should do some testing and see... I am wondering if there is a log like curve that associates to fermenter volume and configuration.

I have been pitching to cell counts for about a year - but cannot say it has dramatically improved things. Anecdotally - I seem to get more consistent fermentations.




Posted 34 days ago.
Edited 34 days ago by mchrispen

homebrewdad
Charter Member
Birmingham, AL
2480 Posts


>Anecdotally - I seem to get more consistent fermentations.

You and me both.  Starters and cell counts seemed to make a huge difference in consistency for me.





Posted 34 days ago.

Catman_bru
SE, WI
7 Posts


Dang, back on the fence about this one. For what it's worth, Oldsock pitched ~1 quart of ''thick slurry' from a surprisingly similar batch to mine (3.75g, ~1.045). Judging by the dates he laid out in his blog posts, he pitched on the cake as soon as he racked off of it, so I don't think he washed it at all. Assumptions, assumptions... He also got ridiculous attenuation compared to my first attempt (11%abv compared to my 9%abv)...


I think I will give it a go. I will probably harvest the cake tomorrow and attempt to clean it up a bit by decanting off old beer and leaving behind old trub. Any thoughts on that would be appreciated as well.




Posted 34 days ago.

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