Yeast harvesting/repitching

I have always scooped yeast out of my buckets with a spoon into a sanitary jar. Never had an issue. As far as how much yeast you need I can not help with that. Good luck.

 

1) You'll most likely be fine collecting either way. Performing an acid wash will help alleviate any worries if you want to go that route.

2) Not sure you mean by, "What if we can't?" Then pitch what you have? Unless you're drastically under, just note how much you pitched and then see how the beer turns out. If you can't get to ~75% of your pitch rate then I'd look into buying more yeast, but I'd roll with anything north of that. Or do you mean, "What if we can't collect only from the middle portion of the yeast?" In that case maybe your viability test will tell you what you did collect, or your solids will suck, or other scenarios, but again, I'd just note what happened and pitch. Doing a forced ferment will also help you establish yeast health.

How are you measuring slurry thickness? I'm assuming you don't have a fuge to spin it down.

 

The Fast (or Forced) Fermentation Test isn't a test of yeast health per se, but rather a test of wort fermentability (with a given strain). It's done by pitching a high cell count into a small sample of wort (from the same wort as will be used for the main batch), and fermenting at a warm temperature to save time. The idea is that whatever final gravity is reached in the test sample should be the lowest possible gravity that will eventually be reached in the main batch. Now, if your main batch doesn't eventually attenuate to near the level of the test sample, that could indicate a yeast health problem (one that was overcome by say, the higher pitch rate in the test sample), but as a yeast health indicator it wouldn't be very useful, because the you've already under-attenuated the main batch.

 

Sorry, I mis-spoke a little bit. You're correct and what I was getting at was that if the main batch has problems the forced ferm will help give signposts of what he should be shooting for.

 

Oh and I forgot about number 3. Why wouldn't you do a viability test? Cheap and takes like 5 minutes.

 

1. Not necessary per say (especially when only planning to repitch once), but ultimately more sanitary.
2. Lagers generally require a pitch rate of 1.5 - 2 million viable cells per ml of wort. (see 3)
3. Doing a viability check is important if you want to get your slurry pitch amount more dialed in (ie by viable cell count rather than weight)

Calculating pitch rate (by cell count):

new batch will be 1 bbl I presume. 117348 ml in 1 bbl
117348 ml x 1.5 million cells per ml = 176,022,000,000 viable cells needed to ferment 1 bbl
176,022,000,000 total viable cells needed / (CELL COUNT per ml of slurry x Viability %) = ml of slurry needed to pitch

So if you don't do a cell count and a viability count you need to guesstimate how much to pitch (by weight or volume) and wyeast has been kind enough to provide you with what they feel is generally a good guesstimate.

 

2) Unless you are using a *very* non-flocculent, it would be odd not to have enough yeast to harvest for one batch. Rule of thumb is you get 3-4x yeast. Even yeasts which you think won't yield much yeast (kolsch, hefeweizen, wit, etc) have never given me issues.

That being said, if for some reason you didn't get enough yeast, you need to understand the effects underpitching will have on your beer (esters, higher alcohols, etc). If the wort is already going, you don't have a lot of options except to ride it out. It's better to make sure you have enough yeast before you mash in, though

 

I assume you put some head pressure on the keg to keep the lid sealed, just remember not to put too much pressure on the yeast or you can damage it. I believe you need to keep the psi under 20 to avoid hurting the yeast and would recommend going much lower than that.