Imperial Stout with not enough yeast

Question

I'm working on brewing an Imperial Stout and using a liquid yeast (WLP-007). Beer Smith is telling me that I need about 300bn yeast cells. However, it says I might get 180bn. I'm usually not a stickler for details but this is a big enough difference that it worries me. I bought 2 packs of the liquid yeast and made a starter (rougly 0.75L). Beer Smith says I should roughly have a 1.6L starter (I only have room for 1 liter though...).

Would it be safe for me to pitch this yeast on brew day, buy two more vials, do a starter for that, and then pitch the second starter a couple days later?

Another option might be to hold the chilled wort for a day or two, make the right yeast starter, and just pitch the correct amount.

Answer 1

Although I trust BeerSmith, I also recommend running your calculations through Mr Malty.

Personally, I would not be too worried. You have a healthy starter and a good number of yeast. I brewed a RIS with a single packet of US-05!

If you are really worried and pressed for time, maybe re-hydrate a packet of US-05 on the side, add it to your starter, give it an hour or two to say hi to the other yeast and then let them start working on the wort. Dry yeast adds approx 110bn cells per 11g packet.

Answer 2

This is a silly: Yeast will reproduce in your beer as long as there's food. A 1 liter starter from a single vial would have been fine for an ale. You'd want at least double that for a lager.

Anyway, if you're worried, rose the yeast when the fermentation does down, and then keep it over 70°F until primary is over. Siphon to a secondary glass carboy, and wait three to five weeks before bottling.