Just listened to this hop chemistry podcast from beersmith,
it's pretty good. James Altwies from Gorst Valley Hops talks about adding some hops well after flameout.
He said if you cool your wort down to 120F and then do a hop addition you'll get some really intense hop aroma.
He talks alot about hop oils and their flavors,
these are his descriptions from the podcast
Myrcene-most of the hop oil, usually 40-60% of the total oil, mellow herbal, boils at 280F or 250F(other sources say 333F)
Humulene-nugget hops, herbal, unique hoppy smell, boils at 150F
Caryophyllene-centennial, citrusy, boils at 110F
Farnesene-saaz,sterling, musty, spicy, boils at 79F
He said you get the grassy flavors mostly from fresh undried hops, Hexanol was the specific compound for grassy.
He also talks about glycoproteins in the wort acting as a soap to capture these hop oils.
If you're interested in hop chemisty give this podcast a listen too,
and the previous podcast on beersmith with Stan Hieronymous is also pretty good,
Stan talks about hops too, and a new book he's coming out with on hops.
This is unrelated to the podcast, but since I'm a fan of Sterling's flavor
which James said is from Farnesene I looked this up on Wikipedia.
Farnesene is emitted by aphids upon death to warn away other aphids, several plants synthesize it as a natural
insect repellent. Also it is the chief compound in the scent of a gardenia flower,
making up 65% of the headspace constituents.