Yeast starter calculation

[Btaz]

I'm looking to make a 22G lager. My thought was to make a 5G batch and use that slurry to repitch. When I use brewer's friend yeast calculator is shows that the 5G batch won't make enough yeast. This does not sound right to me. Thoughts?

 

[Eric_S]

It’s not enough yeast. For ales you can use 1/3 to 1/4 of a fresh yeast cake but 1/2 a fresh yeast cake for going into the same sized batch and similar gravity as previously done.

 

[IslandLizard]

I never thought of that.
Is it because we pitch lagers at a 2x higher rate than ales, so the yeast propagates only 2-3x in a batch instead of 4-5x with ales?

If so, brew two 5 gallon batches. That should give you plenty of yeast for 22 gallons, and some to spare for keeps or another starter batch.

 

[Btaz]

Ok new plan. I need about 1400B cell. Looks like if I take 1 vial (80B cells) and do a 3.5L stater I get about 720B cells. If I take about 100B cells from that starter and do another 3.5L stater I get about another 750B cells. Then a 3rd repeat of 1.75L gets another 415B cells. 720-100+750-100*415 = 1685. Add in some decay from the earlier stater and in there. I'll be getting 5G wort from a local brewery and I'll use half to prep for the lager.