Unfortunately the detailed chemistry on how to get those mangoy and passion fruity flavors out of hops like Citra is still a work in progress... (I am constantly scanning the OSU research for the secrets to coaxing those amazing flavors out of Citra.)
This is the first time I've seen references to the original studies that discovered that it's actually the yeast working on the hop oils (terpenes) that is responsible for these flavors. -Yes this was mentioned in Stan Hieronymous's hop book but he didn't include the references to the original studies. --The first of these studies occurred in 2000!
I'm quickly finding that the IPAs that I like best are late kettle hopped, whirlpool hopped, or hopped during a "hop stand" so I'm very much interested to eventually see how this part of the chemistry works but for now it's good enough to know that those flavors come from hopping prior to the yeast floccing.
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