kombat
Well-Known Member
I've done quite a bit of reading, and I still don't feel like I fully understand the math behind preparing a yeast starter.
I know how to calculate how much yeast I need. That part is easy. 4 billion cells per gravity point per 5 gallon batch, and double it for lagers. Easy-peasy. The areas that are still unclear to me, however, are:
Even after all this reading, and having actually done a few starters myself, I still feel like this is very much a guessing-and-hoping game. Am I alone in this confusion? Am I missing some fundamental truisms that would clear this whole mess up?
I know how to calculate how much yeast I need. That part is easy. 4 billion cells per gravity point per 5 gallon batch, and double it for lagers. Easy-peasy. The areas that are still unclear to me, however, are:
- Say I've collected some washed yeast from a batch, and stored it in a jar in the fridge for 2 months. From what I've read, the yeast cake at the bottom of the jar could vary in cell density anywhere from 1 billion cells per milliliter to 4 billion cells per milliliter, depending on age (viability), and dilution with non-yeast matter (trub). So I just guess 2 billion cells per milliliter and go from there. How can I improve this estimate without buying a microscope and a bunch of petri dishes?
- Say I need 320 billion cells, and I'm starting with a smack-pack. I've read that a 2L starter will double the cell count. But is that true for any given starting cell count? Or will 2L of starter simply grow 200 billion cells, regardless of how many I started with? I mean, if I pitch 100 mL of my washed yeast slurry (at 2 billion cells/mL) into a 2L starter, then that should already be 200 billion cells, right? Will they double to 400 billion in a 2L starter? Or would I need a 4L starter for that? Or what if my 100 mL of washed yeast actually has a lot of dead cells, and actually only has 50 billion viable yeast cells? Will they still "double" to 100 billion in a 2L starter? Or will they grow to 200 billion, because they'll always replicate enough to fill the space they're given (which happens to be 100 billion per liter)?
Even after all this reading, and having actually done a few starters myself, I still feel like this is very much a guessing-and-hoping game. Am I alone in this confusion? Am I missing some fundamental truisms that would clear this whole mess up?