TLDR: I have no idea how much top-cropped yeast to pitch into a ~1.055 OG Octoberfest (5.5 gallons)
I am planning on making an Octoberfest (late I know) on August 18th. Instead of making a boring old starter, I decided to spring for some ingredients and use up the Northern Brewer hops in my freezer and make a steam, which I will do on August 10th. While different from San Fransisco Lager Yeast, Wyeast's bavarian lager has very similar characteristics (and is likely distantly related) to the SF lager yeast typically used in steams.
Anyway, I'm planning on making a 1.5L starter + yeast nutrient with the BL yeast (smack pack), pitching in the low 60s for the steam. Then I am planning on top-cropping as much as I can at high krausen (24-36 hours?) off the steam, harvesting into a sanitized mason jar, and pitching that into my Octoberfest Lager at around 50 degrees.
this being my first lager, I am obviously worried about stressing the yeast, excessive sulphur production, etc., however the proprietor of my LHBS told me that it was not advisable to pitch onto an existing yeast cake. I had heard this wasn't a good idea (but not a horrible idea), as there is a lot of other material in this (dead cells, trub, etc.), but he mainly cited the fact that if you overpitch, the cells won't need to grow, and they will actually competitively crowd each other out/kill each other (!).
I am left with a few alternatives:
1.) top crop and grow a 1.5-2 L starter for the Oktoberfest 2.) top crop and pitch as-is (maybe a cup?)
EDIT: someone on another site just commented that I won't be able to top crop since this is a lager yeast. aka. a BOTTOM fermenting yeast. Even if there is a krausen, it doesn't sound like it will have huge amounts of yeast cells in it. Maybe I'll just reserve some of my steam starter and do a second starter...making this entire exercise circuitous and pointless. Gotta love homebrewing!