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Reusing the yeast cake from prior brews

These are from the What’s Brewing post. I’m copying them to this thread because I didn’t want to hijack that thread.

My concern with reusing the yeast cake from previous brews is that it seems counter to the rule of not leaving the beer on the cake too long. I know that has a lot to do with yeast autolysis, but would the dead yeast and non-yeast components of the trub from prior brews create any off flavors? Since many brewers far smarter than me do it, I have little doubt I have nothing to worry about. But I’m still curious.

I don’t save big yeast cakes. I do skim off a thin layer on top. I say, the stuff on the bottom dropped off… because of what?
I like you’ve got this out for discussion…
Cider, I’ve pitched on the cake of a spent keg… Sneezles61

Well first autolysis is practically unheard of on the homebrew level. It’s also more about the yeast’s cell wall rupturing than about dead yeast.

Just 3 weeks ago I kegged 5 gallons of pilsner and brewed 10 gallons the same day, poured half the yeast cake off to a second bucket and pumped the chilled pils wort into the buckets. I’ll keg that 10 gallons tomorrow. It just so happens I used a new smack pack and starter for the first 5 gals because it was just time after using the previous slurry for about a year and at least 3-4 generations sometimes more.

Sometimes I split cakes like I described but more often is saved slurry. I’m not as picky as @sneezles61 I just leave a little beer on the cake, swirl it up and pour all that will fit into a qt mason jar and store it in the fridge. I don’t generally use all at once, depends on it’s age. Within a week or two I may pitch some without a starter, beyond that I make starters and pitch at high K.

Everyone creates their own process. This works for me. Your mileage may vary.

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This is true about many of the things we worry about as home brewers.

I have dumped my fresh wort on a yeast cake and had good results. Fast start and violent fermentation. But I learned that just pulling some slurry and saving it in a mason jar produced about the same results without as much trub.

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I’ve used a full cake and saved slurry with success. Didn’t notice anything bad from either.

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I make a lot of lagers, so saving yeast from previous batches is essential to the health of my wallet.

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How do you estimate how many yeast cells are in X amount of slurry that is Y days old? I can’t find any online calculators that take those inputs. I know I don’t need to be dead-on accurate with the yeast pitch but, I’d like to know whether I’m pitching 50% of what I need or 200%.

I’ve not used any of those calculators… more of because I can’t get them to work… Technology is my enemy!!!
I save about a 1/4 - to 1/2 cup… Of that nice, creamy yeast… My starter for 10 gallons is 1quart of boiling water and 3/4 cup DME… It all works well… Sneezles61

Ive used the Brewers friend slurry calculator. I have pitched on the cake but usually I’ll save slurry in jars or pour the looser stuff from a spent bucket to a clean one with fresh wort. I mean commercial breweries reuse yeast so why wouldn’t home brrewers

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Do you guys make starters from slurry that is a month or 2 old? I’ve been saving a quart jar full from every brew over the last 6 batches and they are all half slurry have beer on top. I have never used it before but figured I would treat it like any yeast pack and make a 2 liter starter

Well the purpose of a starter is to build up yeast count which you don’t need to do with slurry. That said what I do sometimes is activate the slurry with some wort then pitch at high krausen to jump start a fermenation

Hmm alright. I was thinking it would also ensure viability but using some fresh wort would do that. I want to can a bunch of wort to make staters for next year I just need to borrow a pressure cooker

I have this same question! How does one know when that jar of yeast it the fridge has passed its prime and is in need of a starter to build it back up. Let’s say @Grantmesteven brews once per month. Can he use any of jars for his next brew or should he make a starter for the slurry from 6 months ago and use all the slurry from 3 months ago and maybe just 1/2 the slurry from 1 month ago?

I know I’m probably driving you experienced slurry men nuts with all these questions but, I hate having to learn from my mistakes.

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Anytime you use slurry your probably over pitching. I’ve use year old slurry and just got it going and had no problem. 3 months old I usually just warm it up. I am more worried about mutation than viability. Most of us lager Brewers all reuse our yeast because you need alot more yeast. Don’t worry about viability. I’m so cheap I’ll grab older yeast at the homebrew store at steep discount and make a bigger starter. Those sell by dates are more about moving product than companies worrying about your beer.

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MrMalty has this function (you’ll need to enable Flash for the calc): Mrmalty.com

I did a Kentucky common a few weeks ago… 6 days from fermenter to keg… I lost track of how many pitches my Whites 001 yeast had… It has changed… Has a heffe nose to it… That yeast has been around for just over a year… The brew is very good even if it wants to be a heffe… but i did toss the yeast cake. Sneezles61

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