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Hops
,added new section "Characterizing Hop Flavor and Aroma"
Other '''thiol''' (organic sulfur) based compounds contribute to a pleasant aroma and flavor in beer, such as 4-mercapto-4-methyl-pentan-2-one (4MMP), which is found in high quantities in North American varieties such as Simcoe (highest amount), Summit, Apollo, Topaz, and Cascade hops, as well as varieties from Australia and New Zealand. The character of black currant, muscat-like aroma in beer brewed with these hops has been attributed to 4MMP. It is thought that 4MMP is only found in North American, Australian, and New Zealand hops and not European hops because European hops are often treated with copper ions, which has been shown to decrease the amount of 4MMP in hops. Interestingly, beers brewed with these hops showed a 33% increase in 4MMP after fermentation; it is thought that the precursor cysteine conjugate is responsible for the increase in 4MMP during fermentation <ref name="Kishimoto_2008" />. The volatile thiols 3-sulfanyl-4-methylpentan-1-ol (3S4MP; grapefruit <ref name="Cibaka_2016">[https://www.uclouvain.be/cps/ucl/doc/inbr/documents/JAFC_2016_64_8572_8582.pdf 3‑Sulfanyl-4-methylpentan-1-ol in Dry-Hopped Beers: First Evidence of Glutathione S‑Conjugates in Hop (Humulus lupulus L.). Marie-Lucie Kankolongo Cibaka, Laura Decourriere, Celso-JoséLorenzo-Alonso, Etienne Bodart, Raphael Robiette, and Sonia Collin. 2016.]</ref>), and 3-sulfanyl-4-methylpentyl acetate (3S4MPA; passionfruit, grapefruit <ref name="Cibaka_2016" />) have been identified in Nelson Sauvin hops as the compounds that give these hops their "wine-like, Sauvignon Blanc" character. Similar thiols have been described as the major contributors to the aroma of Sauvignon Blanc wines themselves: 3-sulfanylhexan-1-ol (3SH) and 4-methyl-4-sulfanyl-pentan-2-one (4MSP) <ref name="Kiyoshi_2009">[http://pubs.acs.org/doi/pdf/10.1021/jf8034622 Identification and Characteristics of New Volatile Thiols Derived from the Hop (Humulus luplus L.) Cultivar Nelson Sauvin. Kiyoshi Takoi, Marie Degueil, Svitlana Shinkaruk, Cécile Thibon, Katsuaki Maeda, Kazutoshi Ito, Bernard Bennetau, Denis Dubourdieu and Takatoshi Tominaga. 2009.]</ref>.
==Characterizing Hop Flavor and Aroma==
Hops provide a wide array of aromas and flavors to beer. The hop industry currently provides their own hop flavor and aroma descriptors, but attempts to standardize these descriptors have been made as far back as 1756, and as recently as 1978. More recently, [http://www.mbaa.com/publications/tq/tqPastIssues/2017/Pages/TQ-54-1-0143-01.aspx Drexler et al. (2017)] worked with a perfumer to establish 12 major categories of hop flavor descriptors. Each major category contains more specific descriptors. These descriptors can be measured on a 0-10 scale, and a spider graph can be drawn to represent them. Drexler et al. (2017) proposed that even though expensive gas chromatography is available for hops which measures specific compounds, sensory analysis is still the best way to quantify how different varieties of hops actually smell and taste in beer <ref name="Drexler_2017">[http://www.mbaa.com/publications/tq/tqPastIssues/2017/Pages/TQ-54-1-0143-01.aspx The Language of Hops: How to Assess Hop Flavor in Hops and Beer. Georg Drexler, Elisabeth Wiesen, Mark Zunkel, Sebastian Hinz, Alicia Muñoz Insa, Victor Algazzali, Tim Kostelecky, and Christina Schönberger. 1. Joh. Barth & Sohn GmbH & Co. KG, Nuremberg, Germany. 2. John I. Haas Inc., Yakima, WA, U.S.A. MBAA Technical Quarterly. Vol. 54, no. 1. 2017. Pgs. 34–37. DOI: http://dx.doi.org/10.1094/TQ-54-1-0143-01.]</ref>.
The proposed categories, example hop variety, and the specific descriptors by Drexler et al. (2017) are seen below <ref name="Drexler_2017" />:
# Floral (ex: Ella): Elderflower, Chamomile Blossom, Lily of the Valley, Jasmine, Apple Blossom, Rose, Geranium, Carnation, Lilac, Lavender
# Citrus (ex: Mandarina Bavaria): Grapefruit, Orange, Lime, Lemon, Bergamot, Lemon Grass, Ginger, Tangerine
# Sweet Fruits (ex: Mosaic®): Banana, Watermelon, Honeydew Melon, Peach, Apricot, Passion Fruit, Lychee, Dried Fruit Plum, Pineapple, Cherry, Kiwi, Mango, Guava
# Green Fruits (ex: Hallertau Blanc): Pear, Quince, Apple, Gooseberry, White Wine Grapes
# Red Berries (ex: Monroe): Casss (Black Currant), Red Currant, Blueberries, Raspberries, Blackberries, Strawberries, Wild Strawberries, Cranberries
# Cream Caramel (ex: Triskel): Butter, Chocolate, Yoghurt, Honey, Cream, Caramel, Toffee, Coffee, Vanilla, Tonka
# Woody Aromatic (ex: Relax): Tobacco, Cognac, Barrique, Leather, Woodruff, Incense, Myrrh, Resin, Earthy, Cedar, Pine
# Menthol (ex: Polaris): Mint, Lemon Balm, Camphor, Menthol, Wine Yeast
# Herbal (ex: Columbus): Lovage, Thuja, Basil, Parsley, Tarragon, Dill, Fennel, Thyme, Rosemary, Marjoram, Green Tea, Black Tea, Mate Tea, Safe
# Spicy (ex: Saazer): Pepper, Chili, Curry, Juniper, Aniseed, Nutmeg, Liqorice, Clove, Ginger Bread, Fennel Seeds
# Grassy-Hay (ex: Herkules): Green-Grassy, Fresh Cut Grass, Hay, Tomato Leaves, Green Peppers, Nettle
# Vegetal (ex: Summit®): Celery Stock, Celery Root, Leek, Onion, Artichoke, Garlic, Wild Garlic
See also:
* [http://masterbrewerspodcast.com/039-the-new-language-of-hops MBAA Podcast interviews George Drexler about his study.]
* [https://www.experimentalbrew.com/podcast/episode-42-hopping-and-festing-nick Experimental Homebrewing Podcast talks about the Drexler et al. study (starts at ~36 minutes in).]
==Antimicrobial Properties==
===Glycosides===
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>.