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Home Brew Forums > Home Brewing Beer > Brew Science > Become a Dry Hopping Jedi Master!
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Old 07-29-2013, 10:06 PM   #1
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Default Become a Dry Hopping Jedi Master: That Citra Flavor!

Peter Wolf just went through his Masters of Science commencement in June but on August of last year he published his thesis on "A Study of Factors Affecting the Extraction of Flavor When Dry Hopping Beer"; it was overseen by Dr. Tom Shellhammer (Mr Hop Aroma himself) and the research was funded by the fine folks at Indie Hops.

You may now, for free become a Dry Hopping Jedi Master in only 66 pages!


http://ir.library.oregonstate.edu/xm...lfe_thesis.pdf


These OSU folks just keep turning out more and more amazing research dedicated to making IPAs awesome!


Adam

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Old 07-29-2013, 10:20 PM   #2
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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.



akoi, K.; Koie, K.; Itoga, Y.; Katayama, Y.; Shimase, M.; Nakayama, Y.; Watari, J.
Biotransformation of Hop-Derived Monoterpene Alcohols by Lager Yeast and Their

Praet, T.; Van Opstaele, F.; Jaskula-Goiris, B.; Aerts, G.; De Cooman, L. Biotransformations of
hop-derived aroma compounds by Saccharomyces cerevisiae upon fermentation. Cerevisia
2012, 36, 125–132.

(51) King, A. J.; Dickinson, J. R. Biotransformation of hop aroma terpenoids by ale and lager
yeasts. FEMS Yeast Research 2003, 3, 53–62.

(52) King, A.; Richard Dickinson, J. Biotransformation of monoterpene alcohols by Saccharomyces
cerevisiae, Torulaspora delbrueckii and Kluyveromyces lactis. Yeast 2000, 16, 499–506.



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Old 07-29-2013, 10:40 PM   #3
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Figure 5 here is the Citra flavor "money shot" showing Beta Citronello increasing throughout fermentation and the corresponding decrease of geraniol (the geraniol in the Citra hop gets converted by the yeast to that delicious citronello flavors that we all know and love in a good citra beer). -This is why Citra hops should only be used late and not for dry hopping.

http://www.sciencedirect.com/science...73716311001636


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Old 07-31-2013, 05:49 PM   #4
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you know it's potentially good reading (even for a thesis), when the final statement in his acknowledgements section is


Lastly, thank you for being so delicious, beer! Without you I’d have to study
something awful, like wine…

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