[Pawtucket Patriot]

I've got a pretty nice yeast bank -- probably close to 10 strains at the ready at any given time.  But since I don't use them all with equal frequency, some of them sit for a while between batches, sometimes as long as a few months.  When I use yeast that's been dormant for that long, I obviously make a starter to wake up the yeast.  I use Jamil's pitching calculator to determine how much slurry to pitch to the starter, but there are some things that the calculator does not do that I think would be very useful in this situation.

First, how big of a starter should I make when I just want to rouse dormant yeast?  Does it depend on batch size?  O.G?  Whether it's an ale or a lager?  Is it irrelevant?

Second, the pitching calculator indicates how much slurry to use when doing a straight repitch (i.e., no starter), but is this figure the same even when I pitch to a starter first?  I presume there will be a growth factor involved when I pitch to a starter and, therefore, I'll end up with more viable cells with a starter than I would with just pitching straight to 5 gallons of cooled wort.  Should I compensate for this by reducing the volume of yeast I pitch to a starter?  If so, by how much?

[a10t2]

Sorry if you've already seen this, since I know I've linked to it before, but I think it will answer both questions. Or give my rationale, anyway.

http://seanterrill.com/2010/03/23/yeast-ranching-and-you/

[Kaiser]

Sorry if you've already seen this, since I know I've linked to it before, but I think it will answer both questions. Or give my rationale, anyway.

http://seanterrill.com/2010/03/23/yeast-ranching-and-you/

Sean,
I noticed that you use low gravity starter wort and Jamil’s calculator. How does this calculator account for the gravity of the starter wort?

Matt,
If the yeast is older than 3 weeks  (just a guess on my side) I’d take a small sample and grow up a new culture. I’d be worried about having too much old yeast in the yeast pitch if the yeast is simply woken up.

Kai

[Pawtucket Patriot]

Thanks for the link, Sean. I've visited your site before, but I actually hadn't seen the yeast page. I'll give it a more thorough read when I get home from work.

Kai, when you say take a small sample, what amount do you have in mind?  

Here's a practical example of my current practice. I brewed a Helles in December with a healthy pitch of 1st generation Wyeast 2206 (2 smackpacks in a 2L starter). I harvested that yeast when fermentation was complete on December 18. Last night, I made a 2L starter (with DME, 1.040) and pitched approximately 250 ml of the harvested 2206 slurry. This morning, the starter is chugging away nicely. I will let it ferment out today, cold crash it tomorrow, and then decant and pitch to a 1.050 schwarzbier on Sunday.

Problem with my method is that it isn't based on any calculable estimation. Basically, I just make a starter of the same volume I would have made if I had used a fresh smackpack (if that makes sense). Then I just pitch the amount of slurry indicated in the "slurry" section of the Mr. Malty calculator.

[Kaiser]

Kai, when you say take a small sample, what amount do you have in mind? 

Maybe a teaspoon full.

Problem with my method is that it isn't based on any calculable estimation. Basically, I just make a starter of the same volume I would have made if I had used a fresh smackpack (if that makes sense). Then I just pitch the amount if slurry indicated in the "slurry" section of the Mr. Malty calculator.

If the initial amount of yeast is small compared to the final amount of yeast, yeast growth largely depends on the amount of sugar (starter  volume x starter strength) and how the yeast is raised (still vs. intermittently shaken vs. stirred). It becomes a bit more complicated when the initial yeast amount closer to the final yeast amount. In this case a significant amount of sugar is used to revitalize the old yeast cells and predicting yeast growth is not that simple anymore.  Although you’ll probably need less sugar in the starter to get the same final yeast count since you are starting out with more yeast and are not solely relying on converting “sugar” into yeast.

But that’s not why I’m advertising the use of only a small amount of yeast. I just like the idea of having all fresh and new yeast. Many brewers do it like you do, i.e. refresh old yeast, and don’t seem to report problems. I’d would have to run a side-by-side to see how much beer quality is to be gained from using freshly grown yeast.

You can estimate the amount of yeast by letting the slurry settle, decant all the beer on top of it and weight the slurry. This works well with heavy flocculators like WY2206 but it does require that you know the weight of the starter vessel. I have the weight of all my flasks marked on them for exactly that reason.  Based on a few data points I have so far each gram of dense yeast slurry tends to contain 4-5 Billion cells. I think that matches Jamil’s date for dense slurries.

Kai

[a10t2]

I noticed that you use low gravity starter wort and Jamil’s calculator. How does this calculator account for the gravity of the starter wort?

I do propagate most things at about 8°P. I think, although it doesn't say explicitly, that Jamil's calculator assumes roughly 10°P wort is used. For the most part, I just round up to the next liter and call it close enough. I'm not doing cell counts (at home, anyway) but based on weight and volume measurements it ends up reasonably close to what the calculator predicts. I'm also both stirring and aerating continuously, so that probably offsets the lower gravity to a certain extent.

One of these days I'll bring a slurry or two into work and double-check using the hemocytometer. Frankly, I'm just not concerned about variations of 10-20%.

[Kaiser]

Frankly, I'm just not concerned about variations of 10-20%.

Yes you should not expect more precision than that anyway.

Kai

[maxieboy]

Can one determine how many cells are left after fermentation?  I washed my yeast for the first time yesterday(went well) and thought if I can divide it into approx 100 billion cells per container, I could treat each essentially as a tube/smack pack for subsequent starters. I guess yeast ranching qualifies as one of my 2011 brewing goals.  

[dzlater]

Can one determine how many cells are left after fermentation?  I washed my yeast for the first time yesterday(went well) and thought if I can divide it into approx 100 billion cells per container, I could treat each essentially as a tube/smack pack for subsequent starters. I guess yeast ranching qualifies as one of my 2011 brewing goals.  

I am not sure this would work , but it might get you close
maybe someone else can confirm
go to the pitching rate calculator http://www.mrmalty.com/calc/calc.html
click on the"repitching from slurry" tab
check the"calculate viabilty from date" box
set the date to whenever you harvested the yeast
set the "yeast concentration" slider bar to thin slurry
hit the calculate button
this will show you yeast needed and ml of slurry
take that ratio and step it up till you get the  100 billion to whatever ml
so if it says
336 billion and 397 ml
(397*100)/336
you would need about 118 ml of thin slurry for 100 billion cells

[dzlater]

In regards to the original question of how big a starter to make from a harvested slurry.
I had the same question on another forum and this is the answer I was given.
I can't take credit for this.

Let's say I'm making a 1.060 ale, pitching 5.5 gallons. I have a jar of reharvested slurry that is exactly four weeks old from today, and the yeast is very compacted into a 50mL puck. I go to Mr Malty, set the parameters of my beer, set the age of the yeast, go to the "Reharvesting" tab, set the Yeast Concentration to 4.0, set the Non Yeast Percentage to 15.

Mr Malty says that I need 229billion healthy yeast cells, which would be 134mL of my yeast in its current state. I have 50mL, or 37% of what I need (50/134). If you multiply 37% by 229billion cells, you find that I have about 84billion healthy cells.

Here's where things get fuzzy. As I understand it, the Mr. Malty calculator works such that a vial of yeast with 100% viability has 100billion cells. So if I have 84 billion cells, this is the equivalent of having one vial of yeast at 84% viability, right? So then I flip to the Liquid Yeast tab, manually set my viability to 84%, set the Growth Factor so that it says I need 1 vial. Doing this, it says I need to make a 1.23L starter with a stir plate.

[Pawtucket Patriot]

That's helpful dzlater -- thanks for posting!

[skyler]

Kai - what are the potential drawbacks to building up, say, a 3L stir-late starter with 333mL of 3 month old unwashed slurry? If I were to follow your method of using a teaspoon, should I start with a 1L starter and "build up" or could I just pitch 1 teaspoon of old slurry into 3L of starter wort and put it on the stir-plate?

[Kaiser]

Kai - what are the potential drawbacks to building up, say, a 3L stir-late starter with 333mL of 3 month old unwashed slurry? If I were to follow your method of using a teaspoon, should I start with a 1L starter and "build up" or could I just pitch 1 teaspoon of old slurry into 3L of starter wort and put it on the stir-plate?

I'd be worried about the autolysis products that would be introduced into the beer. In particular enzymes that degrade proteins. While there is lots of mention of this Protease A enzyme I'd have to design and conduct an experiment to see if I can notice an effect.

I think just a tsp of yeast in a 3 l starter would be fine.

Kai