I used to take the yeast cake from 10gal batches, rinse them lightly then decant and transfer to whitelabs vials. I used them just like store bought. Pitched the same way, and had very good results. Sometimes a little slow start but usually no discernable difference. I still have more wlp001 than I know what to do with...

I wouldn't think they would be pure by any means. Even rinsed yeast isn't pure. However, if you were thorough in your sanitization and keeping bacteria out of the beer/wort, then there really shouldn't be anything in that would ruin your beer or impart any nastiness.
In regards to the propagation - I usually make a 700-800mL starter for my batches, but keep in mind I am only brewing 3 gallon batches. If you are able, I would probably step up the starter one more time to approx 1000ml @ 1.040-1.050.
I read an experiment a while back (will see if I can find it) about measuring yeast by weight rather than volume. I have been messing around with it a little.
I take a measurement of my flask, empty (w/ stir bar) in grams. Run your starter as per usual, cold crash it and decant as much of the liquid off as humanly possible. Then you would remeasure the weight of the flask, subtracting the difference.
I cannot get a definite measurement on the amount of cells per gram for the yeasts I use, but in the article the yeast used averaged 2.5-4 billion cells per gram.

Example:

1000mL flask - 423g (w/ stir bar)

run starter, cold crash, and decant.

1000mL flask w/ yeast cake and stir bar - 506g
difference of 53g
53g(2.5 b/g approx )= 132.5billion cells.

Like I said, I have only been playing with this, but it seems to work well for the batches I have used this method on.

Evan_B said:

I wouldn't think they would be pure by any means. Even rinsed yeast isn't pure. However, if you were thorough in your sanitization and keeping bacteria out of the beer/wort, then there really shouldn't be anything in that would ruin your beer or impart any nastiness.
In regards to the propagation - I usually make a 700-800mL starter for my batches, but keep in mind I am only brewing 3 gallon batches. If you are able, I would probably step up the starter one more time to approx 1000ml @ 1.040-1.050.
I read an experiment a while back (will see if I can find it) about measuring yeast by weight rather than volume. I have been messing around with it a little.
I take a measurement of my flask, empty (w/ stir bar) in grams. Run your starter as per usual, cold crash it and decant as much of the liquid off as humanly possible. Then you would remeasure the weight of the flask, subtracting the difference.
I cannot get a definite measurement on the amount of cells per gram for the yeasts I use, but in the article the yeast used averaged 2.5-4 billion cells per gram.

Example:

1000mL flask - 423g (w/ stir bar)

run starter, cold crash, and decant.

1000mL flask w/ yeast cake and stir bar - 506g
difference of 53g
53g(2.5 b/g approx )= 132.5billion cells.

Like I said, I have only been playing with this, but it seems to work well for the batches I have used this method on.

Great info there thanks. I've not heard of of pitching by weight, that's interesting...

To clarify my purity note... My question is more about how much of the sample is good active yeast and not hot break and other miscellaneous stuff. I'm not too worried about bacteria and wild yeast. My sanitation is pretty good by homebrew standards.

Evan_B said:

I have had pretty good luck rinsing yeast. It's a question of how many times you want to rinse it, and how steady you can decant, but you could get those little soldiers pretty darn clean I would imagine.

Orrrrrrrrrr.... if you are fermenting in the plastic buckets

per Wyeast:

" Open Top Fermenters / Top Cropping:
Harvesting yeast from the top of open fermenters (top cropping) is still a widely used practice in the modern brewing industry. Specific yeast strains which rise to form a dense head must be used, making top cropping nearly exclusive to ale and wheat strains. As with other methods of harvesting yeast, harvesting a consistent population which avoids the extremes is important.

Yeast should be harvested once fermentables have been reduced by 50% or more. The timing of the skim should be consistent from batch to batch to help maintain fermentation profile. A head will rise approximately 24-36 hours into fermentation. The first “dirt” skim containing trub should be discarded as should the final skim. The middle skim should be harvested and used."

This seems like it would allow you to cut out most of the trub and junk. You should probably still rinse it once.

this is definitely a good/easy way to harvest yeast from a solid top fermenting ale yeast.... if you ferment in buckets or other vessels with a large openable top. I did this once when i still used buckets, and it worked great.

I think it would be possible ... but rather awkward to do with carboys ... and I'm not sure just how

FromZwolle said:

ceannt said:

I think it would be possible ... but rather awkward to do with carboys ... and I'm not sure just how

turkey baster.

Or a small lattle..

In either case it would be a miserable experience$

Tasty McDole from the brewing network uses a siphon to top crop. Never tried it, but seems feasible as well as the turkey baster. Of just use a silly straw, suck up the yeast and spit it in a cup. I'm sure the bacteria in your mouth is overrated as bad and will probably help when brewing a nice sour beer.
:-q

Benvarine said:

Tasty McDole from the brewing network uses a siphon to top crop. Never tried it, but seems feasible as well as the turkey baster. Of just use a silly straw, suck up the yeast and spit it in a cup. I'm sure the bacteria in your mouth is overrated as bad and will probably help when brewing a nice sour beer.
:-q

Getting spit in beer goes way back ... from the mantioc beers of the south Pacific to the corn beers of Latin America .... gotta have enzymes in there somehow for conversion .....