What lager yeast to use for what

So, I am planning to do 7.5 gallons of 1.050 lager tomorrow, 5 gallons of one and 2.5 gallons of another. I'm torn as to what yeast to use. I have a 1.5L starter going full steam now with a smack pack of Wyeast North American Lager. I also smacked a Wyeast Pilsen Lager (because I thought my starter was no good). I also have a packet of W-34/70 on standby.

My Malty says I need 350 billion cells for my 5 gallons and that a 1.1L starter with 2 vials/packs would do it. I'm probably good with the starter I have, right? That would leave the other smack pack for the smaller 2.5 gallon batch, but is that enough yeast? I need 175 billion cells, but the smack pack probably has about 125 billion, right? Am I risking underpitching at that level? I'm wondering if I should combine 2 of the 3 and use the odd one for the other batch.

Thoughts? What might you do in this situation? Thanks.

I also have a 2nd Pilsen smack pack, but I'd rather not waste another $7, especially on a 2.5 gallon batch.

What kind of lager is it? I would just pitch the yeast that is appropriate for the style.

You are underpitching with just the smack pack...I would say they are somewhere around 100 billion; at least, that's the number I see thrown around in various literature.

Looks like you're right on the cell count. Any of the lager yeasts I have would be suitable. I guess I'll pitch 2 of the Pilsen smack packs, since even if I start a starter tonight, it's not enough time to multiply before tomorrow afternoon. Just going to make for an expensive case of beer, but then I'll be sure to wash and reuse the yeast for the next lager.

Pitching enough yeast for a lager can be both time-consuming and expensive. With respect to your current batch, you might be underpitching but you can partially overcome this by adjusting your fermentation temperature. I almost always pitch cold, but if I were short of yeast I'd consider a warmer pitch (mid-to-high 50s) then cool it to around 50 when you see signs of fermentation. Also pay careful attention to aeration in this case; you want the yeast you DO have to have optimal conditions.

One thing to consider is to line up at least a couple of lagers back-to-back. You'll have waaaaayyy more than enough slurry from this batch to ferment your next batch (in fact probably at least enough slurry for two batches). That cuts your yeast cost per batch in half--and you can go half a dozen batches (at least) this way; way more if you start rinsing your yeast. If you are careful and do that properly it'll keep a really long time so next time you want to make a new batch...treat it like a smack pack and just make a starter!

Another thing to consider if you're going to do lagers now and then, as opposed to a bunch back-to-back and you don't like the trouble of smack packs, starters, potentially underpitching, etc. is to just use dry yeast. W-34/70 is my favourite but I've had good success with S-23 as well (especially at warmer temps [like, high 50s] for those who have to ferment their lagers using a swamp cooler or ambient basement temperatures) and am experimenting now with S-189. Wake up on a Saturday, decide "Hey, I'm gonna brew a lager today!" and you can rehydrate and pitch no problem.

Good luck!