Using recycled yeast with Brewfather - how to calculate pitch rate?

[muppix]

Morning Gang!

I've got what looks like 300 ml of yeast salvaged from my last brew, and want to try using this in a fresh brew, basically just to see if I can do it. Going forward I'm going to (over) build starters rather than pitching from sachets, but I'm waiting on equipment to arrive and want to have a little play. Originally this yeast was 2 sachets of WLP001 that I used for a session IPA and it's been stored in a clean plastic beaker in my brew fridge, having been removed from the brew before I dry-hopped. Looks pretty healthy.

Anyway, I've put together a recipe for a basic pale ale using odds n sods from my inventory, but when it comes to adding east into that recipe I'm a little bit stumped. How do I account for half a soup container that was (is?) WLP001? My best guess was to identify it as WLP001 Slurry, but I don't want to end up over- or under-pitching and, as you can see, have no real clue what I'm doing. Decant the beery head, chuck the whole lot in, hope for the best?

 

[muppix]

Quick update: I decided to pitch the whole lot and hope for the best. No nutrient was added (I only remembered that I had some in stock after the boil) but I did aerate the chilled wort liberally with pure oxygen between kettle and FV just before pitching the yeast, which I did by removing the top layer of old beer using a wine thief and then spooning the yeast slurry directly into the fermenter. Airlock activity started an hour later albeit slowly, though by the 12 hour mark it was chugging along nicely.



There was maybe 4 or 5 inches of head space in my 25 litre SS bucket (hard to tell with all the foam after aeration) and 24 hours into primary I noted some Krausen in the airlock so I swapped it out for a blow-off tube ending in a beaker of sanitiser. Difference in temperature between FV and ambient was nearly 4 ℃ - absolutely incredible.

Since then it's slowed down a lot and is only bubbling lightly every few seconds instead of the almost constant stream at the start. I'm at 1.012 against my target of 1.009 (OG 1.045) which Brewfather / Tilt tell me equates to 4.3% ABV and, more importantly, 73% attenuation. I'm very happy with that and may well try to salvage this yeast a second time, but it may be more difficult as I can't remove it from my SS bucket before dry-hopping as easily as I could from the Fermzilla. I heard somewhere that dry-hopping works better when the yeast has dropped out, so with that I may cold-crash for a couple of days and rack to another vessel before dry-hopping, which will also let me harvest the yeast more cleanly from this one. Or I may skip that extra step (and cleaning) and just throw the hops into this FV since the cake at the bottom will separate to some degree on its own, and I don't need to harvest a great quantity anyway now that I have a stir-plate and Erlenmeyer flask to play with.

 

[Galena]

I have never harvested yeast, and as you have discovered you really need to know your starting cell count to use the calculator, I cannot speak of harvested yeast but when making a starter then the packet is usually 100Bn cells and if you calculate to overbuild by 100Bn cells and then put by the suggested amount then your starting cell count each time will be 100Bn cells. If you input the date you made it as the manufacture date then it will account for cell loss due to age.
I guess you can't really do that if you have harvested an unknown quantity, but it's all guesswork to some degree anyway.