quantity of yeast slurry

[nosdunk]

disclaimer. (DONT SHOOT THE NEWBIE) I know this has been visited in other forums and threads but would like to ask a unique version of this questions. I want to make sure I understand the process properly. I need to learn about the proper amount of slurry to collect and pitch.

I am brewing 1 bbl batched of Kolsch. After the great help from the other thread regarding cold crashing, I have collected the yeast from the bottom of the conical. I opened the butterfly valve and allowed the clumps of yeast to fall out until it turned to a slurry. I collected approximately 3/4 of a growler of yeast slurry from the conical. I would estimate the slurry to be more of a medium thickness slurry.

My OG is around 1.052 for the beer I am brewing. I am targeting batched of 35 gallons to accommodate some waste. Based on the information I have been able to find, I believe I need to around 3/4 of a liter of slurry into the wort for fermentation. Since I am new to repitching yeast from a slurry, does this sound like an appropriate amount?

[GlacierBrewing]

To know for certain how much you should be repitching, you need to do a yeast count. You dilute a sample of yeast, place on a specialized microscope slide (haemocytometer), count the yeast cells within the grid and do the appropriate calculations. Great resources for this at www.brewingscience.com. It's not as difficult as it sounds.
Luck to you.

Prost!
Dave

[OneMoreBrewer]

To know for certain how much you should be repitching, you need to do a yeast count. You dilute a sample of yeast, place on a specialized microscope slide (haemocytometer), count the yeast cells within the grid and do the appropriate calculations. Great resources for this at www.brewingscience.com. It's not as difficult as it sounds.
Luck to you.

Prost!
Dave

What he said. The weight is a better measurement than the volume, however neither will give you an accurate yeast pitch measurement. Ideally you would separate the liquid from the yeast by centrifuge and weigh the difference. Use what he said, for simplicity.

[a10t2]

The only other way I know of to get an accurate "count" is serial dilution. At 1 million cells/mL, a sample of yeast in water will be visually clear.

Using a cytometer is both faster and more precise, though.

[dick murton]

I assume from the size of the kit that you don't have a centrifuge, and probably don't have a lab vacuum filtration facility.

So the only way I know of that you can do with any semblance of success is to reslurry what you have already collected, then take a small sample of that slurry, putting it in a previously weighed test tube or equivalent small diameter tube - you could probably even use a piece of blanked off plastic pipe. It doesn't have to be strictly hygienic as you won't re-use that small quantity of yeast. You want two or three inches of slurry in the tube. Leave to settle as long as possible, ideally overnight plus, in a fridge, to encourage it to settle. The following day, decant off what hopefully then is pretty clear beer from the top. Assume the "solids" left are about 60% yeast. You can then work out the consistency of the yeast slurry, and calculate how much to add. If it is any sort of guide, we used to pitch at about 0.3 kg viable yeast / 100 litres wort for ales, and about 0.7 kg viable yeast 100 litres wort for lagers, allowing for dead cell count. Again, I assume you don't have a microscope, so assume dead cell count of 10% - hopefully it is actually less than that, i.e. divide the nominal weight of yeast required for your wort volume by 0.9, so you add more weight of yeast to allow for the proportion of dead cells.

You need to have very sensitive scales for this to be anything like accurate, but you are more likely to be able to pick up a set of scales at short notice and at reasonable cost, reading in grams to a decimal point (you need this level of accuracy becasue of the small sample volume)than a microscope. Or you could use graduated tubing and work on volume, assuming yeast and the supernatant beer all has the same PG.

[nosdunk]

Thank you for the replies.

I will be purchasing a microscope ASAP.