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Hops
,udpated Glycosdies again
Hops contain glycosides, which are flavor compounds that are bound to a sugar molecule. In their bound form, glycosides are flavorless. Studies on hop compounds elude to the possibility of compounds being produced by glycosidic activity of ''S. cerevisiae'', however direct evidence of glucosidic activity in ''S. cerevisiae'' is lacking. Daenen (2008) reviewed the glycosidic activity of many strains of ''S. cerevisiae'', and found that only a few strains expressed any real glucosidic activity and none that exhibited exo-beta-glucosidase which would be required to break glycosidic bonds in the beer/wort. Daenen did find that enzymatic activity from some strains of ''Brettanomyces'' can efficiently release these bound compounds and release their flavor and aromatic potential <ref name="Praet_2012" />. Beta-glucosidase enzyme can also be added to beer to enhance the breakdown of glycosides and intensify hop-derived flavors and aromas. For example, one study showed an increase in citrus, orange, grapefruit, and tropical pineapple in a Cascade dry hopped beer that had beta-glucosidase enzymes added to it <ref>"Optimizing hop aroma in beer dry hopped with Cascade utilizing glycosidic enzymes (presentation slides)." Kaylyn Kirkpatrick from New Belgium Brewing Co. Young Scientist Symposium, Chico, CA 2016.</ref>. There is also some evidence to support that there is higher glucosidase activity in seeded hops, which are generally not used in the brewing industry <ref>"Seeded and "Unseeded Hops - a Quality Comparison (presentation slides)." Martin Zarnkow. EBC 2015.</ref>. See the [[Glycosides]] page for details.
However, much of the work on hop derived glycosides has been done using hop oils. Sharp et al. (2017) found that when using pure beta-glucosidase extract on beer hopped with whole leaf hops that the amount of increased monoterpenes such as linalool, terpineol, citronellol, nerol, and geraniol is small and insignificant. The fatty alcohol 1-octanol (waxy, green, citrus, orange, aldehydic, fruity <ref>[http://www.thegoodscentscompany.com/data/rw1021071.html Octanol. The Good Scents Company. Retrieved 03/31/2017.]</ref>) was the only measured flavor compound that was increased significantly <ref name="Sharp_2017">[http://onlinelibrary.wiley.com/doi/10.1002/jib.418/abstract The effect of hopping regime, cultivar and β-glucosidase activity on monoterpene alcohol concentrations in wort and beer. Daniel C. Sharp, Jan Steensels, Thomas H. Shellhammer. 2017.]</ref>. The alcohol 1-octanol can be esterified into octyl acetate, which is a classically "citrusy" aroma, so perhaps certain yeasts can create this ester during mid-fermentation hopping <ref>[https://www.facebook.com/groups/MilkTheFunk/?comment_tracking=%7B%22tn%22%3A%22R%22%7D Preiss, Richard. Milk The Funk Facebook group. 03/31/2017.]</ref>.
See [[Glycosides]] for more information.