I am on a kick experimenting with dry yeast. Part of my experiment is to just dump the pack into the wort rather than pre-hydrating it. I know I will lose some yeast cells doing it this way, but If I’m going to prep yeast I’ll do a yeast starter. To me the advantage of dry yeast is that it is quick (well, and cheaper).
My question is: at what gravity level does under pitching become a concern? My next brew is an AIPA with an OG of 1.058. Will one pack do, or should I add a portion of a second? In case it matters the yeast in question is US-05.
I’ve always pitched a second pack at 1.070+ and only recently started rehydrating. I’ve never had any ill effects,ie., always had good attenuation and yeast character. Disclaimer - I prefer liquid cultures but I’ve used a ton of S05 for short notice brewing.
EDIT - I think Denny said he’ll go to 1.075 on one packet.
I am along the lines with Hoosier. If my wort is over 1.075 I will consider adding a bit more from a second pack, but I always have rehydrated with great results. Under 1.075, 1 pack will suffice with no issues (providing proper aeration).
I do a house beer at 1.060 and one pack of us-05 does just fine. I have pitched dry quite a few time with no issues. Let us know how it works out for you.
I wouldn’t worry too much about under-pitching ales until the pitching rate gets below about 0.5 million/mL-°P (assuming you’re targeting 0.75). If a pack of dry yeast contains ~200 billion viable cells, that would be around 1.080 OG for rehydrated yeast, or 1.040 for un-rehydrated. Ultimately, though, let your tastes decide.
For ales - up to 1.075 gets 1 pack of unrehydrated S-04 or US-05. For lagers I’d pitch two packets of 34/70 for anything up to a smallish doppelbock. If I only have 1 pack and I’m at the borderline of gravity for 1-pack, then I’d consider rehydrating as an insurance policy.