Pitching by Weight

[PediosDoom]

All,
It seems there is a wealth of resources for brewers about pitching by volume but not for pitching by weight. Our brewery has a yeast brink on load cells without an in-line flow meter. I am hoping that someone knows of any good resources for pitching by weight. I found a previous thread on Probrewer about this topic here:

http://discussions.probrewer.com/showthread.php?1178-How-do-you-determine-pitching-rates-by-weight

One of the contributors (who has not been active on Probrewer for a year) listed a standard formula for determining pitch amount based on slurry density, pitch rate, brewlength, and OG to find BBLS of yeast needed then stated: "Mutliply this number [BBLS of yeast] by 31 then by 8.5 to give you pounds of yeast to pitch."

For the life of me, I can't figure out where the magical "8.5" in their equation came from or how you would convert gallons of yeast to lbs of yeast. Is there an approximate weight for a given volume of yeast slurry or a way to determine that for our yeast strains?

Any help is much appreciated.

Thank you,
PD

[WinchesterHaus]

"Mutliply this number [barrels] by 31 then by 8.5 to give you pounds of yeast to pitch."

Not sure where the 8.5 was picked, exactly, but water weighs 8.345 pounds per gallon.

To calculate the weight of your slurry: (weight of full container - empty weight of container ) / # of gallons of slurry = weight of slurry per gallon.

Then the equation for weight of slurry: numbers of bbls as discussed in previous thread x 31 (which is the gallons in a barrel)

That gives you the number of gallons of slurry needed.

Take the number of gallons x weight of slurry from above = total weight of slurry required.


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[jebzter]

"Mutliply this number [barrels] by 31 then by 8.5 to give you pounds of yeast to pitch."

Not sure where the 8.5 was picked, exactly, but water weighs 8.345 pounds per gallon.

To calculate the weight of your slurry: (weight of full container - empty weight of container ) / # of gallons of slurry = weight of slurry per gallon.

Then the equation for weight of slurry: numbers of bbls as discussed in previous thread x 31 (which is the gallons in a barrel)

That gives you the number of gallons of slurry needed.

Take the number of gallons x weight of slurry from above = total weight of slurry required.


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So you're saying I would need 2000+lbs of yeast slurry to pitch in a 10bbl tank? 10bbl x 31 gal x 8.5lbs =2635gal.lb.

This is straight from white labs:
Re-Pitching By Weight or Volume:

Ales with a specific gravity < 1.064 (16°P): pitch 1.0 Kg (2.2 lbs.) of thick slurry (40% yeast solids) per 1 bbl or 1 Liter (1 quart) of thick slurry per 1 bbl
Lagers with a specific gravity < 1.064 (16°P): pitch 2.0 Kg (4.4 lbs.) of thick slurry (40% yeast solids) per 1 bbl or 2 Liters (2 quarts) of thick slurry per 1 bbl
High lagers with a specific gravity > 1.064 (16°P): pitch 3.0 Kg (6.6 lbs.) of thick slurry (40% yeast solids) per 1 bbl or 3 Liters (3 quarts) of thick slurry per 1 bbl

I follow the white labs guide lines and have been very successful, though I will be moving towards yeast counts and pitching by volume soon. Just to be more precise.

[schmogger]

From Wyeast's website

Re-Pitching By Weight or Volume:

Ales with a specific gravity < 1.064 (16°P): pitch 1.0 Kg (2.2 lbs.) of thick slurry (40% yeast solids) per 1 bbl or 1 Liter (1 quart) of thick slurry per 1 bbl
Lagers with a specific gravity < 1.064 (16°P): pitch 2.0 Kg (4.4 lbs.) of thick slurry (40% yeast solids) per 1 bbl or 2 Liters (2 quarts) of thick slurry per 1 bbl
High lagers with a specific gravity > 1.064 (16°P): pitch 3.0 Kg (6.6 lbs.) of thick slurry (40% yeast solids) per 1 bbl or 3 Liters (3 quarts) of thick slurry per 1 bbl

[Bainbridge]

Yeah it's the old 'a pint's a pound the world around' theory. Even though yeast slurry probably weighs just a bit more than water.

Recently we changed how we do our cell counts to solve this. Used to be we started our dilutions with 10ml of yeast slurry and 90ml water, then 10ml of that and 90 ml of water for a 100:1. Now we go by weight, so 10 gm of yeast, 90ml of water (since a ml of water is a gm of water anyway). Working backwards from the cell count, we can figure out how many cells per gram of yeast we have and from that how many kilos to pitch. Which usually just works out to about 2lbs per barrel, just like wyeast said. But sciencier!

[PediosDoom]

"Mutliply this number [barrels] by 31 then by 8.5 to give you pounds of yeast to pitch."

Not sure where the 8.5 was picked, exactly, but water weighs 8.345 pounds per gallon.

To calculate the weight of your slurry: (weight of full container - empty weight of container ) / # of gallons of slurry = weight of slurry per gallon.

Then the equation for weight of slurry: numbers of bbls as discussed in previous thread x 31 (which is the gallons in a barrel)

The 8.5 possibly takes in to account the average weight of yeast cells plus water?

I suppose my issue with this calculation is that our yeast brink has no way of determining the volume of slurry inside. The only data we have is the weight given by the load cells and the slurry density determined from taking a sample from the brink (which I'm almost certain varies with time and stratification within the brink).

I suppose the only way to extrapolate would be to take a small sample and weigh it. Weight of slurry per gallon could then be calculated.

[PediosDoom]

From Wyeast's website

Re-Pitching By Weight or Volume:

Ales with a specific gravity < 1.064 (16°P): pitch 1.0 Kg (2.2 lbs.) of thick slurry (40% yeast solids) per 1 bbl or 1 Liter (1 quart) of thick slurry per 1 bbl
Lagers with a specific gravity < 1.064 (16°P): pitch 2.0 Kg (4.4 lbs.) of thick slurry (40% yeast solids) per 1 bbl or 2 Liters (2 quarts) of thick slurry per 1 bbl
High lagers with a specific gravity > 1.064 (16°P): pitch 3.0 Kg (6.6 lbs.) of thick slurry (40% yeast solids) per 1 bbl or 3 Liters (3 quarts) of thick slurry per 1 bbl

This is the general rule that we have been using for years now. While it is fairly good for most fermentations, it does not account for a slurry thinner or thicker than one with 40% yeast solids (we often see slurries that differ). The result is rather inconsistent pitch rates and thus rather inconsistent fermentations. As a midsize brewery shifting its focus to efficiency and consistency in quality, we are seeking a more precise method. Our goal is to test slurry prior to brewing and then tailor exact pitch weights to each OG/brewlength.

Yeah it's the old 'a pint's a pound the world around' theory. Even though yeast slurry probably weighs just a bit more than water.

Recently we changed how we do our cell counts to solve this. Used to be we started our dilutions with 10ml of yeast slurry and 90ml water, then 10ml of that and 90 ml of water for a 100:1. Now we go by weight, so 10 gm of yeast, 90ml of water (since a ml of water is a gm of water anyway). Working backwards from the cell count, we can figure out how many cells per gram of yeast we have and from that how many kilos to pitch. Which usually just works out to about 2lbs per barrel, just like wyeast said. But sciencier!

This is excellent info! Sciencier is just what I'm looking for. Can you walk me through how you work backwards? Are you assuming that the difference between 10mL of water and 10mL of yeast slurry is negligible?

[kai]

I miss having a yeast brink with load cells.

When I did work with one, we worked off pitching the same weight as you would volume, which is obviously easy in metric and has been expressed in this thread already.

In terms of slurry density, that is an issue whether you are pitching by weight or by volume, and I find the best rule of thumb is a sight glass and a brewer's calibrated eyeball.