I've a niggle to get out my findings on this subject given that I've been rumbled writing posts with little credit given to whoever it was driving me to dig up those findings. And only now I realise the "Bloke" post (above) is on a different forum. That wasn't plagiarism, that was research! And I'm a bit of a tart when it comes to which forum I do what on (i.e. no preference; though this forum might get more cleverer answers but the other forum just gets more answers).McMullan wrote: ↑Sat May 16, 2020 1:33 pmI'm really not sure what was supposed to have happened (or didn't) to be so anxious, let alone to be 'picking over the lessons learnt'. It was a fermentation, not a national crisis. Perhaps you should discuss it with this bloke. He seems to know what he's typing about
So, my old method of building starters (based on monitoring SG) was flawed. I was using yeast starter calculators to predict the outcome but felt uncomfortable with how they worked (like "target pitch rate"; well the yeast will know what type of beer it's destined for and act accordingly … won't it?) and how to know where it's all at? And I was mixing up "scientific stages" ("lag phase" and the like) with "observable stages" ("not doing anything yet" through to "it's trying to climb out of the flask"). When does one stage finish and another start? That's easy, when the yeast has built up the numbers it needs it goes on to getting on with fermenting. And the yeast knows the numbers it needs because you selected the appropriate "target pitch rate" … err .
It seems obvious to me now; The calculators can only work within a month, perhaps two, of the yeast pack being manufactured. Outside of that you must rely on experience, guesstimates and a bit of luck. I'd read up a bit on "vitality", the seemingly missing parameter in the calculators because how do you put a figure on "vitality" (the calculators base their calculations on "viability" or cell count). "Vitality" is the yeast's "get up and go". It's the difference between fermenting in two days and fermenting in two weeks for the same cell count.
So, after much though and messing about (I'm good at the latter) I came up with this approach to "calculating" vitality. The yeast starter calculator I use is "Homebrew Dad" ("BrewUnited") which has the key feature of supporting multiple step starters: I'd concluded that for problematic and old yeast packs I needed to allow the yeast's "vitality" to catch up with it's "viability" and for that it will need time. So instead of starting with a 500-800ml starter, I'll start with 200ml (or smaller?). And the next step will be 600ml, and the next 1800ml, etc. (for a 45L batch). 18-24 hours between steps (as normal). So having reached a starter of over 2L the calculator will be predicting sufficient cell count and "vitality" should be in good order too?
This multiple "stepping up" is the same as folk coaxing yeast out of a bottle. Or starting yeast from a slope culture. Or even culturing the best from a commercial yeast pack using only a tiny sample from it.
My thanks to "McMullen" and "f00b4r" for setting me on this course, although they probably both resent being implicated by me in the babblings of a lunatic.
Next up: Practical illustration of it working (perhaps too well!).