So, N3QX, would it make sense to make lots more starter than I need before doing a cell count? Once I know how many cells per mL, I can decide from there how much starter to pitch, without having to go back and regrow my starter if my cell count is too low. That way I can put starter on the stir plate Thursday, measure it Friday, and brew Saturday. Would you foresee any adverse effects from doing it that way? And is one day long enough to grow it up, or is 2 better?
Thanks!
Well, yeah, it would make sense. You don't want to pitch the entire starter anyway; I know it's mentioned in the literature, but it's never made sense to me. Why pitch all that diluent into your beer? Chill the whole starter flask, decant the starter 'beer', and pitch the slurry.
So: If you want to ensure you have enough yeast for a Saturday brew, first calculate how much slurry you need. You can use the Mr Malty online pitching calculator or you can do the arithmetic yourself - see my
brief tutorial in the HBT Wiki.
Once you've determined how many ml of yeast slurry you'll need to inoculate your wort, you can estimate how much bother you'll need to go through with your starter. If, to follow the Wiki example, you determine you need 228 ml of slurry, you need to modify the amount because your starter slurry is a
lot more pure than slurry harvested from a ferment. Harvested slurry is only about 25% yeast; your starter culture is -
should be - almost 100% pure. So you can reduce the amount needed accordingly. If you want to be conservative - and who doesn't? - call it 80% pure. And since 1 ml of yeast solids contains approximately 4.5 billion cells, you can easily compute the amount of slurry you require.
Brewing up the starter in a measured container means you can start your starter a week before brewing. If you discover the first go-round has produced enough yeast, just cover it and keep it refrigerated. If the first go-round hasn't produced enough, you've got several days to step up the starter.
Brew it up, ferment it, chill it, see how much slurry settles out. If you need more, repeat. Simple!
Bob