Yeast Trub re-use (Long post - sorry)

[UKSkydiver]

I have read many many threads and articles and I am getting myself into a right tizz. I think I want a simple yes or no, but please let me expand.

I am planning on brewing a Doppelbock tomorrow. It should be on the 1074 region and about 15 litres, It will be no chilled so I'm probably looking to pitch on Tuesday morning.

I am planning to re-use yeast from a California Common (MJ Cali Common yeast) The Cali Common was about 5% and fermented at 16-18c, no off tastes, no dry hopping. I used a full packet for an 11.5 litre batch, so in theory not stressed. I brewed seven weeks ago and bottled five weeks ago.

After bottling, I simply transferred the trub into a sanitised jar and left in the fridge at about 6c

Definition: For the purposes of this thread, when I say trub, I mean the sludge at the bottom of the fermenter. Everything.

On Friday I decided to rinse the yeast, I know this may not be necessary or advised. I rinsed with cooled boiled water and everything sanitised.

I left the **** to settle out and poured off the remaining top section of water and yeast. Long story short, I've ended up with about 0.5 litre of slurry.

Definition: For the purposes of this thread, when I say slurry, I mean the water and yeast suspension.

In order to try and either increase, or to prove viability and vitality of the yeast, I have made a starter. 100g DME to 1 litre water, boiled for 10 mins and cooled. I aerated a bit by transferring to a conical flash and pitched the 0.5 litre slurry. It's been on the stir plate for ~12 hours at ~12c (remember this is cali common and I have now moved this to room temp ~18c)

My assertions:
Information elsewhere suggests that one third of yeast trub can easily be used to ferment a subsequent batch. I have used a full load of trub therefore one could argue that I have started with three times the amount of yeast needed for a standard brew.
Accounting for accidental removal of some yeast through the rinsing process, let's say I have ended up with double.
And sticking this in a starter on a stir plate should at least double again, right?

The bit where I'm getting myself in to a tizz is the calcs. Well, not the calcs themselves, more trying to come to a consensus on the glut of information.

The pitch rate calc on Brewer Friend suggests 448bn and BrewFather suggests 537bn, so not far off. 500bn is a nice round number.

This article ( Defining Yeasts Slurries and Dealing With An Overcarbonated Keg: Mr Wizard - Brew Your Own (byo.com) ) explains how to measure yeast densities from slurry and to calculate how much slurry is needed.

My 0.5 litre of slurry is pretty dilute at ~ .2bn cells per ml (I have put 25ml in a graduated cylinder for about 15 hours and it has about 2.5ml yeast (x4) = 10% solids. I'm not sure where he gets his .0254 and .0096 from but I assume that is what he refers to a 'standard curve equation', but certainly my result aligns with the graph on the page.

If I then go on to the next part of the calcs. he says "Number of yeast cells needed = 1 million cells/mL/°Plato x 13 °Plato x 17,000 mL of wort"

and that calc aligns with the calc in this article ( Yeast Harvesting / Re-Pitching | Wyeast Laboratories ) where it quotes 1-2million cells / ml / 1xplato

Lets round up to 1.5million

So put all that together gives:

1.5 million cell/ml/plato x 18 x 15,000 = 405 billion - ok, short by about 100 billion, but that could be my 1.5 million cells, maybe I need to up that to 2 million as it's a big lager which would bring me up to 540 billion which aligns more with both previous calcs.

500bn cells / 0.2 bn cells per ml (density) = 500/.2 = 2500ml - so I would need 2.5 litres of my origianl dilute slurry to pitch into 15 litres of 1074 wort.

So what I don't get is that in theory I already have twice the amount of yeast from trub rinse needed to ferment a subsequent (standard) brew, but according to the calcs, I need five times as much slurry as I started with.

Does a 1070 brew really need that much extra?

So the yes / no question is, having put 0.5 litre of 10% yeast slurry in a 1 litre starter, will that be enough for my brew (I do not know how much a starter replicates)

Given my actions so far, how many cells might I end up with in the starter?

Do I need to rebuild (or just pitch that and another packet of lager yeast?)

So many questions, hence the tizz. Thank you for taking the time to read this far.

 

[matt76]

So you've spent ages trying yourself in knots and then spent a load of time writing this long rambling post...

... All of this to save yourself, what, £2.50 maybe on a packet of dried yeast?

Why exactly?

No, seriously, ask yourself why are you doing this?

Homebrewers seem to be a thrifty bunch at times and in my experience it's easy to get caught up in this and feel like you need to do everything at absolute minimum cost, without pausing to consider why and what the consequences might be.

If your aim is to minimise costs and/or you genuinely want to get into the detail of cell counts and pitching rates then by all means carry on - we all derive enjoyment from this hobby in different ways.

And if you do want to confuse yourself even more, I found this explanation from @saccharomyces useful.

To answer your question, I haven't checked your numbers but on the basis yeast health is more important than cell count I reckon your starter is probably ok.

Rule of thumb I use for my 10L-ish batches, for moderate gravity ales I tend to pitch half a pack of dried yeast, or a full pack for lagers. For high gravity (e.g. Baltic Porter, OG 1.080+) I would double that. Having said that, my last Baltic Porter I just went with 1 full pack of CML Hell and it was fine. Cali Common you're probably going to ferment warmer and 1.070 is a bit lower so I reckon a single pack or equivalent is probably sufficient for 10L or so.

 

[cushyno]

Your original 1/2 litre of slurry would probably have been enough without needing to build up further.

If my memory notes serve me right, the average slurry with yeast, some trub and any hop debris gives about 1bn cells per ml.

My notes:

Pitching from Slurry

1bn cells = ~0.5ml of starter slurry if it doesn't contain any trub. ~1ml of slurry from beer without much trub.
250ml of slurry is approx 1/3 of slurry from a 23l batch (my estimate)
214bn cells is good enough for a 1.050SG batch.

Yes, the yeast viability decays over time, but you would have been close enough re-pitching all of your saved trub without washing or needing to build cells with a starter. As @matt76 says, having good yeast health is most important, so whatever small starter you have done will help.

See these links on cell counts if you want to blow your mind further:
Estimating Yeast Cell Counts in Fresh Starter
Estimating Yeast Cell Counts in Fresh Starter
http://braukaiser.com/blog/blog/2012/11/03/estimating-yeast-growth/
WoodlandBrew/

 

[UKSkydiver]

Hey Matt
Thanks for your thoughts and response.

Cost isn’t my main driver. If I take into consideration my time whether brewing, bottling, cleaning, researching, forum posting, as well as equipment and ingredients, like anyone else, it would probably be way cheaper to just get beer from the supermarket.

That said, it’s always good to either save on or reuse resources, whether that’s plastic, water use or yeast, etc.

Some people pressure ferment, or use kegs, or brew all grain or whatever. Wanting to reuse yeast, for me, is wanting to improve knowledge and processes and try new things. This is probably a big part of my discomfort. Until we’ve done something a few times, and know what the results are, what you can and can’t get away with, it’s all new territory.

I feel like I should probably already have this in my arsenal by now, but it’s not something I’ve really done before. On reflection I should have probably started with some standard brew and not a high gravity lager, but we are where we are.

In terms of rambling , I like to provide detail. Whenever someone asks, “Why is my brew xxxx?” invariably the responses are: what is your recipe / what is your process / what have you tried / etc I wanted to provide detail around what information I had used to come to the position I’m at, along with references / what my thought processes were / how I had come to any conclusions or questions. Showing my working out, for want of a better expression.

Back to the topic in hand. (And yes, I have read all of saccharomyces posts - there is a lot of info which I find makes a lot of sense) Part of this was realising I needed (according to some calculation or other) 4 packets of yeast which I didn’t have so I thought I could culture something up.

Anyway, I have done a stepped starter, starting with 1 and then a 2 litre starter. If I understand saccharomyces correctly, the max you can get in 1 litre of starter is 200bn cells, so in theory, I will only get 400bn, which is slightly under, but within 90 mins I will have 800bn. So assuming that is correct, everything will be fine and I will make beer.

Again, thanks for making the time to read and reply,

 

[UKSkydiver]

See these links on cell counts if you want to blow your mind further:

Thank you @cushyno for taking the time. I will read up on those once my head has cooled down