How come wyeast activator smack packs need a starter? I thought the purpose of the nutrient pack inside acts as a starter...I thought just the propogator packs need a starter...
First off, Wyeast says "The Wyeast Activator (125 ml) smack-pack is designed to directly inoculate 5 gallons of standard ale wort (O.G. < 1.060, 65-72°F)". But if you look at the tech info on their website, you'll see the numbers don't quite work out. They claim 100 Billion cells in a smack pack. Their tech info says that, for something less than 1.060, you should pitch 6.0 million cells/ml. Even with exactly 5.0 gallons (most times it's closer 5.5 or 6.0), that comes out to 114 billion cells and there's only 100 billion in the smack pack. That also assumes 100% viability in the smack pack which is about impossible so you're actually getting less than 100 billion.
This thread started about an "over 6% IPA" which most likely puts it into the "greater than or equal to 1.060". For that, Wyeast says you need 12.0 million cells/ml. That comes out to 228 billion - a smack pack doesn't even come close.
And to really open your eyes, go to mrmalty.com and check out that pitch rate calculator. It's pitching rates are more realistic (rather than Wyeast's that are more of a sales pitch to make you think a smack pack is "pitchable") and you'll see that 5.0 gallons of 1.060 wort should have 208 billion cells (not Wyeast's 114). Again a smack pack isn't even close.
The nutrients in the smack pack aren't intended to make it into a "starter". They're there so that, when you smack the pack, the yeast have something to feed on to make the pack swell. That feeding/swelling only proves that there's live yeast in there - it really doesn't accomplish anything in the way of cell count growth.