I made a mistake of under pitching (I think) this weekend into an Altbier. Chilled the wort in the fridge over night down to 55F. Rehyrdrated one packet of US-05, aerated for a minute with pure O2. 36 hours, no activity, raised temp to 60, nothing. Ended up pitching another packet last night and have a krausen forming this morning. I probably should've pitched 2 packs. Gravity was 1.050 for 4 gallons (that's the batch size I brew these days). Plus I rehydrated at 95F for 15 minutes, then pitched right into the wort, that probably wasn't the best idea either...An 11 gram packet should be plenty for 4G of a 1.050 beer. They are twice the size of Red Star packets.
+1 it sounds like you maybe got a dead packet of yeast. properly rehydrated 1 packet of us=05 should have been more than enough for that batch. 95 for 15 minutes sounds good. did it get kind of creamy and goopy?
Do you mean you aerated the yeast that was rehydrating for 1 minutes of pure o2? cause it's possible you killed the yeast with that.