I've been reading the recipe for Avery DuganA in Mitch Steele's IPA book and want to give this a shot. One thing that worries me is that they ferment at 20 c let the yeast get to 50% attenuation and then let it free rise to 23.4 c to finish out with fermentation complete in 4 days. I've always assumed that i really shouldn't go much over 20 c or i would get too much diacetyl, does diacetyl take affect before the yeast reaches 50% attenuation? What is the benefit for the rise in temperature for an IPA?