Question about Mr Malty's Pitching calculator

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Danek

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I'm going to be pitching a big beer (around 1.100) onto some yeast from a previous batch. I gather that using the whole yeast cake isn't the best option, so I had a look at JZ's pitching calculator to find out how much yeast to use (the calc's at http://www.mrmalty.com/calc/calc.html for those who haven't seen it). The "Repitching from slurry" option suggests that I need around 200ml of yeast for my next beer. My question is, what exactly do I need 200ml of? Is that just 200ml of thick slurry, or 200ml of pure yeast separated out from the slurry? In order to measure out 200ml of stuff, I was anticipating mixing in some pre-boiled water to the yeast cake (as per the yeast-washing thread) - but then that would make the slurry much less thick, and proportionally much less yeasty, which would presumably throw off the calculations. Could anyone shed some light on this?

Thanks in advance! :mug:
 
I can not directly answer your question about washing and pitching rates, but I thought I would share a recent similar experience. I brewed up a fairly heavy APA (OG 1.08), let that ferment completely, then pitched a barleywine (OG 1.097) on top of that yeast cake. The Nottingham took it to 1.012 in 2 under weeks.

I know that it was probably way overpitched according to the calculator, but it seemed to work very well. Taste (hydrometer sample) so far after 2 weeks is surprisingly good. If you are looking for a very clean ferment with little flavor contribution from the yeast I think overpitching is less of a concern. From what I understand, beers that benefit from yeast flavor (Belgians, some English varieties) may not do as well if overpitched, e.g. they may lose some of those ester-y characteristics that make them what they are.

Edit: Just looked in your sig. :) Strong Dark Belgian... You may want to wait for someone who knows more than me.
 
After you finish washing, the sludge/slurry that settles at the bottom of your vessel is the yeast slurry you want to use/measure.
 
If you're pitching onto a cake...dump it in there and leave it alone!
Why would you think it's not a good idea to use the whole cake?
I'm making a big Belgian beer, and according to Jamil's podcast and book, and assorted posters on here, yeast contribute some desirable flavors during their growth phase. If I pitch on the whole cake, there won't be a growth phase, and hence I won't get the flavors from it. I'm sure pitching on the entire cake would get the beer fermented out OK, but as I'm going to be aging this one for a year or more, I thought I'd try to make it as good as I can, to make the waiting worthwhile.
 
I'm making a big Belgian beer, and according to Jamil's podcast and book, and assorted posters on here, yeast contribute some desirable flavors during their growth phase. If I pitch on the whole cake, there won't be a growth phase, and hence I won't get the flavors from it. I'm sure pitching on the entire cake would get the beer fermented out OK, but as I'm going to be aging this one for a year or more, I thought I'd try to make it as good as I can, to make the waiting worthwhile.

But you are not going to be aging the beer on the yeast cake for a year or more, so using the whole cake, in a big beer would be fine. Then after primary fermentation is complete you'll be racking to either a secondary or to bottles for bulk or bottle aging. The aging period would leave sufficient time to clean any off flavors that may or may not have developed from the yeast.

But in answering you original question, I have always wondered the same myself about Jamil's calculator. I've always treated the amount as "suspended slurry," the yeast swirled in whatever liquid I was using, be it starter wort or preboiled water from washing.
 
But you are not going to be aging the beer on the yeast cake for a year or more, so using the whole cake, in a big beer would be fine. Then after primary fermentation is complete you'll be racking to either a secondary or to bottles for bulk or bottle aging. The aging period would leave sufficient time to clean any off flavors that may or may not have developed from the yeast.
Just to clarify, I'm not worried about autolysis - I'll be racking it to secondary after six weeks or so, and then keeping it there for a year, so I'm not concerned about getting off-flavors from the yeast. But as s3n8 says, some Belgian yeasts impart estery flavors during their growth phase, which is a good thing. I'm trying to use Jamil's calculator to pitch an amount of yeast that's (i) small enough so that the yeast will need to reproduce a little, thereby imparting nice flavors, whilst (ii) still being a large enough amount to ensure all the sugars get fermented out. It's a bit of a balancing act.

As I'm going to be freezing some of the yeast for a yeast bank anyway, I guess I may as well wash the whole lot and then draw off the amount from the settled slurry, as DaleJ suggests. All this faff makes me nostalgic for the good old days when I just tore open a pack of US-05... :D
 
For Revvy and BigKahuna - the OP is correct, overpitching can and does exist.

Yeast produce esters and phenolics as a byproduct of their reproduction stage - which in Saccharomyces occurs before fermentation begins. These chemical compounds aren't necessarily bad - we want the esters and phenolics in Belgians and Hefes, etc.

If you are innoculating the wort with too much yeast, they do not go through this initial reproduction period, and instead move right to fermentation. This is why it's bad to have fermentation start super quick. It is also bad to overpitch, because then the yeast go through natural selection - the better yeast will consume the available sugars, and since there's more yeast - there's less available sugars, shutting out the weaker yeast. When the weaker yeast can't cycle through fermentation correctly, then they're going to give off flavors of their own, or perhaps even die - possibly leading to autolysis.

To answer the OP's original question - I would guess you're looking at the entire slurry - trub and all. I would recommend just adding around a cup or two of boiled, cooled water, and swirl it all around. Pour it out into a container that you can measure in (or have pre-measured). Let the slurry/water settle back out and you'll be able to measure the necessary yeast/slurry from there. HTH.
 
I used the calculator for a Belgian with an OG of 1.080 that I'll be brewing tonight. The calculator told me I needed a 1 gallon starter, or 273 billion cells. The Wyeast smack pack says "100 billion cells", and it's only 4.25 fluid ounces. 4.06L (the calc gave me) = ~137floz. Someone's math or biology seems horribly awry.

Here's the math from the Mr. Malty site:
The Math

If you're curious, here is the simple math to calculate the number of cells needed. For an ale, you want to pitch around 0.75 million cells of viable yeast (0.75 million for an ale, 1.5 million for a lager), for every milliliter of wort, for every degree plato.

(0.75 million) X (milliliters of wort) X (degrees Plato of the wort)

* There is about 3785 milliliters in a gallon. There are about 20,000 milliliters in 5.25 gallons.
* A degree Plato is about 1.004 of original gravity. Just divide the OG by 4 to get Plato (e.g., 1.048 is 12 degrees Plato).

So, for a 1.048 wort pitching into 5.25 gallons you need about 180 billion cells.

(750,000) X (20,000) X (12) = 180,000,000,000
It fails to take exponential growth into account, and therefore estimates much higher than actually needed. When fermentation of glucose occurs, yeast have a growth rate of ~0.45hr^-1 (max), which is something like each cell reproduces every 0.037 minutes, or 2.2 seconds, assuming there is enough available glucose of course.
 
I always use this calculator when I'm repitching.

If it comes back at 200 ml, pitch [ame=http://www.google.com/search?hl=en&q=convert+200+ml+to+oz]7-8 fl. oz.[/ame] of the slurry (decant as much of whatever beer is left as you can) into a new fermenter with your new wort.

I do this depending on the style, for exactly the reasons that Chef states above. If I'm repitching Nottingham I'll just drop my wort right on top of an existing cake already in a fermenter. I recently repitched WLP570 and WLP320, both of which produce a lot of esters that are key to the styles that I was making, so I used JZ's calculator to calculate the proper amount of slurry to pitch.

Did you asjust the harvest date? I'm not sure if it's correct or not but I always enter the date that I brewed the batch that created the slurry in this field.
 
The problem with the slurry volume is 3 fold:

- how thick
- how much yeast vs. trub
- how viable is the yeast

thickness is easiest if you let the yeast settle out into a cake and use the thick slurry setting (far left).

Determining the amount of trub is a little more difficult. You could wash the yeast to get it mostly separated, but that doesn't work so well with lager yeast (my experience). If you don't do that and had a fair bit of trub in the fermenter, you can safely assume 30-40% trub and double the amount of yeast to pitch. That should also take care of the reduced viability.

Viability. He has a calculate from harvest date, but I don't think that will be accurate if the yeast sat in the primary for a few weeks already. I'd see harvest date as the time when most of the fermentation was done. At that point a lot of the yeast is lying dormant in the yeast cake.

My guideline would be to pitch twice the volume shown when set to thick slurry.

Kai
 
Aha! I was just about to email Jamil, and came across this - http://www.mrmalty.com/calc/menu.html - when looking for his email address. It's a help page for the Mr Malty calculator, and the section on "Repitching from slurry", at http://www.mrmalty.com/calc/repitch.html , has more info on each of the options. Specifically in relation to yeast thickness, it says this:

"If you've ever seen the yeast packed hard into the bottom of a White Labs vial, that is Thick Yeast, at 4.5 billion cells per ml. When you harvest a yeast slurry and it has settled for a few hours, that is a thin slurry. Usually, most homebrewers will let their yeast settle for a few days in the fridge between one batch and the next. When you do, you'll notice the yeast has settled a bit and is sort of jelly-like. That is the default setting on the calculator. You'll need to estimate from there for other yeast thickness, but what is most important is keeping track of what you pitched and the results you get from the beer. If you need to adjust up or down, that is OK, just keep track of how you do things each time."

So I guess I should have RTFM...
 
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