Re Using Yeast Cake from Primary

[goin2brew]

Would it be reasonable to re use my yeast cake several times? or would I be pushing my luck and end up with poor results.

I know re using the yeast cake once is ok, but how about 3 and 4 times? I planned to move slightly higher in gravity and color with each additional batch.

1st batch is American Pale Ale
2nd batch is American Brown Ale

3rd batch is Porter
4th batch is Chocolate Stout

Thanks in advance,
Damian

 

[Clann]

I'm not an expert but i think after 1 or 2 times the yeast will become stressed and preform sub-par. perhaps you could harvest the yeast and make a starter and nurse the yeast back to health.
Mabye somone more knoledgeable will correct me or add to this

 

[Bob]

You can do that. It's better to harvest your yeast and care for it, though. It's also wise to pitch an appropriate measured amount of yeast; knocking out onto a "cake" doesn't measure the pitch.

Cheers,

Bob

 

[bullinachinashop]

If your going to harvest the yeast, I would at least partially wash it by adding 2 or so quarts of spring water to the cake, give it a good swirl, let it sit for 20 minutes and then pour off about 1/2 qt. Use the 1/2 qt as your pitch.
This should go multiple generations without any issues.
I wouldn't recommend pitching directly if you have the ability to separate the yeast from the trub.
Bull

 

[goin2brew]

Bob,
It makes sense to clean them up and prepare them for the next round. So when the yeast is harvested, what is the method used to calculate/estimate how many you actually have so you can have the correct size pitch?

 

[kpr121]

There was a guy on here that went 19 straight times with one batch of yeast. He dumped 3/4 of the trub and just pitched onto the rest. Let me try to find it...

Ok here it is: https://www.homebrewtalk.com/f163/19-batch-yeast-cake-died-196498/

I'm planning on try to see how far I can go with one yeast cake. I already have 4 brews from the same WLP005.

 

[DrawTap88]

Ok here it is: https://www.homebrewtalk.com/f163/19-batch-yeast-cake-died-196498/

That is a crazy great thread. Thanks for shareing that.

 

[goin2brew]

kpr121.... just the answer I was looking for.
Thanks a million.

 

[kpr121]

Glad I could point you in the right direction. Ever since I saw that thread (and others like it) I've been very stingy with my yeast. I feel like I shouldn't throw it out, like I feel when I accidentally throw a beer bottle in the trash. I even attempted to save some nottingham yeast the other day. What does that stuff cost, like a buck a pack?

I wanna get into yeast washing so that I can keep a nice stockpile of different yeast in the fridge. It just seems insane to have to pay 6-7 bucks extra for every brew session to buy more yeast.

We all got into homebrewing at some point thinking that it would save us money (I've now realized that my equipment cost will probably never be recouped, but still like having 2 cases of beer for "30 bucks")

 

[Bob]

Bob,
It makes sense to clean them up and prepare them for the next round. So when the yeast is harvested, what is the method used to calculate/estimate how many you actually have so you can have the correct size pitch?

The easiest way is to to go to http://www.mrmalty.com/calc/calc.html and use the calculator. Click the "Repitching from Slurry" tab and dig in.

If you want to actually dig into brewing science, do your own calculations.

JZ on Mr Malty specifies 0.75 million cells per milliliter of wort per degree Plato for ales and 1.5 million for lagers. These are good numbers, and they're the numbers the Calculator uses.

I prefer simpler numbers, for several reasons.* I use a number in the middle.

I want one million active cells per milliliter of wort. The arithmetic is pretty easy when one number is 1, too. Let's assume a 5-gallon batch of wort.

(1 million cells) x (ml of wort) x (°Plato)

or

1,000,000 x 20,000 x (1°P) = 20,000,000,000 cells

If you use "1 million" you can reduce the formula to:

20,000,000,000 x (°Plato)

For every °P you need 20 billion cells.**

Now, how much viable yeast is in the slurry in the bottom of your fermenter? Without a yeast laboratory, there's no way to know for certain, but we can make some well-educated estimates. There's between 4 and 5 billion cells in a milliliter of pure yeast, but a slurry (cake) isn't pure yeast; you can expect 1.2 billion cells in a fresh slurry.

So if you need, say, 240 billion cells (to pitch a wort of 12°P or 1.048 OG), you need:

240/1.2 = 200 ml of slurry

It's really easy once you do it a couple of times. It's the formula I was taught to use in my professional-brewing apprenticeship, and it's served me extremely well over the years. It's slightly overpitching ales and slightly underpitching lagers, theoretically, but not so much as I've ever noticed a difference.

Cheers!

Bob

* Homebrewers who can actually count active cells are vanishingly rare. A middling number gets you close enough for success without going overboard, investing in a yeast laboratory.
** http://www.fermsoft.com/gravbrix.php - SG to °P conversion table.

 

[goin2brew]

Thanks Bob.
I'll try to capture and repitch with my next batch and see how it goes.