13,584
edits
Changes
Hops
,→Thiols
===Acids===
'''Alpha acids''' (also called "humulones" and abbreviated as "α-acids") in hops mostly consist of humulone, cohumulone, and adhumulone. Trace amounts of other forms of humulones are also present but are difficult to quantify and currently have limited research: posthumulone, perhumulone, adprehumulone, and adprehumulone acetohumulone <ref name="Hao_2020">[https://www.tandfonline.com/doi/full/10.1080/03610470.2020.1712641 Junguang Hao, R.A. Speers, Heliang Fan, Yang Deng & Ziru Dai (2020) A Review of Cyclic and Oxidative Bitter Derivatives of Alpha, Iso-Alpha and Beta-Hop Acids, Journal of the American Society of Brewing Chemists, 78:2, 89-102, DOI: 10.1080/03610470.2020.1712641.]</ref><ref name="Leker_2022">[https://www.tandfonline.com/doi/abs/10.1080/03610470.2022.2079944 Jeremy Leker & John Paul Maye (2022) Discovery of Acetohumulone and Acetolupulone a New Hop Alpha Acid and Beta Acid, Journal of the American Society of Brewing Chemists, DOI: 10.1080/03610470.2022.2079944 ]</ref>. The ratio of these individual acids to each other can vary based on hop variety much like total iso-α-acid percent, though generally the primary acids are humulone and cohumulone. Cohumulone has been identified by some researchers as a source of a more harsh bitterness, although similar research contradicts this statement <ref>[http://www.scielo.br/scielo.php?pid=S0100-40422000000100019&script=sci_arttext&tlng=es Fundamentals of beer and hop chemistry. Denis De Keukeleire. 1999.]</ref>. Being hydrophobic, alpha acids are mostly insoluble in wort at typical brewing pH (alpha acids become much more soluble as the pH rises towards 5.9 to 7, which is not typical for wort production <ref name="Bastgen_2019">[https://www.tandfonline.com/doi/full/10.1080/03610470.2019.1587734 Influencing Factors on Hop Isomerization Beyond the Conventional Range. Nele Bastgen, Tobias Becher & Jean Titze. 2019. DOI: https://doi.org/10.1080/03610470.2019.1587734.]</ref>). During boiling, alpha acids are isomerized into iso-alpha acids (also called isohumulones) that are soluble. Isomerization leads to roughly a 70%/30% split between diastereomeric isomers called ''cis'' and ''trans'' iso-α-acids respectively, with ''cis'' iso-α-acids being more stable over time and more bitter<ref name="Schönberger and Kostelecky, 2012"> [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2011.tb00471.x/abstract Schönberger and Kostelecky, 2012]</ref>. Alpha acids themselves do not taste bitter, but isomerized alpha acids (iso-α-acids/isohumulones) contribute to the bitterness of beer and have antimicrobial properties. Isocohumulone is often cited as being more harshly bitter than the other iso-α-acids, but studies of taste perception of individual iso-α-acids have not agreed with this. However, iso-cohumolone is slightly more soluble than the other acids and therefore a hop with a higher cohumulone composition may result in a beer with higher iso-α-acid for hops of equal iso-α-acid percent and use in brewing but different iso-α-acid breakdown<ref name="Schönberger and Kostelecky, 2012"/>. Alpha acids are susceptible to oxidation and the alpha acid content of a hop will decrease with storage.
There is evidence to show that during wort boiling iso-humulone and perhaps also iso-cohumulone bind with the head forming proteins, Lipid Transfer Protein (LTP) and Protein Z, to help form foam-positive structures in beer. These iso-alpha acids bind less so with LTP than they do with Protein Z. The resulting bound structures have been described as "vesicles", which are protein "bubbles" (but with no gas in them) with thick surface layers <ref>[https://www.sciencedirect.com/science/article/pii/S0268005X19325391 Vesicular structures formed from barley wort proteins and iso-humulone. Yi Lu, Peter Osmark, Björn Bergenståhl, Lars Nilsson. 2020.]</ref>.
'''Beta Acids''' (lupulones) are similar in structure to alpha acids and have the analogous individual beta acids (lupulone, colupulone, adlupulone, prelupulone, postlupulone, adprelupukone, and adprelupukone acetolupulone <ref name="Dušek_2014">[http://pubs.acs.org/doi/abs/10.1021/jf501852r Qualitative Determination of β‑Acids and Their Transformation Products in Beer and Hop Using HR/AM-LC-MS/MS. Martin Dušek, Jana Olšovská, Karel Krofta, Marie Jurková, and Alexandr Mikyška. 2014.]</ref><ref name="Hao_2020" /><ref name="Leker_2022" />) to individual alpha acids. In their original form, beta acids do not contribute to the flavor of beer because they are not soluble in beer unless the pH of the boiling wort is significantly raised to around 7 pH (which is not typical in brewing conditions) and the original gravity is relatively low (2-8°P) <ref name="Bastgen_2019" />. They are also not able to isomerize during wort boiling. Beta acids do not become soluble in wort or beer unless they are chemically modified by a process such as oxidation <ref name="Algazzali_2014" />, nor are they soluble in beer when dry hopping <ref name="Maye_EBC2017">John Paul Maye. EBC 2017 Presentation. 2017.]</ref>. Oxidized beta acids are soluble and can contribute to bitterness in beer. Oxidized beta acids are discussed more under [[Hops#Acids_2|aged hops]].
====Isomerization of Alpha Acids====
The isomerization of alpha acids into iso-alpha acids is mostly dependent on alpha acid content of the hops, time (to a certain extent), temperature, original gravity, hop rate (hop weight), and IBU saturation. Other variables also affect isomerization to a lesser extent such as pH and calcium concentration <ref>[https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1964.tb06356.x CHANGES IN HOP ACIDS CONCENTRATIONS ON HEATING IN AQUEOUS SOLUTIONS AND UNHOPPED WORTS. H. O. Askew. 1964.]</ref><ref name="Malowicki_2005">[http://pubs.acs.org/doi/abs/10.1021/jf0481296 Isomerization and Degradation Kinetics of Hop (Humulus lupulus) Acids in a Model Wort-Boiling System. Mark G. Malowicki and Thomas H. Shellhammer. 2005.]</ref><ref name="justice_2018">[https://www.mbaa.com/publications/tq/tqPastIssues/2018/Pages/TQ-55-3-1205-01.aspx Tracking IBU Through the Brewing Process: The Quest for Consistency. Aaron Justus. Director of R&D and Specialty Brewing, Ballast Point Brewing. MBAA TQ 2018; vol. 55, no.3. https://doi.org/10.1094/TQ-55-3-1205-01.]</ref>. The higher the gravity of wort above 1.050 SG, the more proteins coagulate and drop iso-alpha acids out of solution (lower gravity worts are not affected by this). During fermentation, yeast cells can absorb iso-alpha acids, which results in further loss of iso-alpha acids in the finished beer <ref name="Bastgen_2019" />. Lower flocculating yeast strains tend to reduce the IBU in finished beer more than high flocculating yeast <ref name="justice_2018" />. Significant isomerization of alpha acids can occur in water without sugar at all (temperatures around boiling are still required), which is relevant in the production of [http://www.garshol.priv.no/blog/331.html "hop tea" in traditional farmhouse brewing] where hops are steeped in hot water for some time, and this is said to extract bitterness from the hops <ref name="Malowicki_2005" /><ref>[http://www.ijbbb.org/papers/161-E005.pdf Kinetic Modeling of Hop Acids during Wort Boiling. Yarong Huang, Johannes Tippmann, and Thomas Becker. 2013.]</ref><ref>[http://www.garshol.priv.no/blog/331.html Lars Marius Garshol. "Raw ale". Larsblog. 05/06/2015. Retrieved 12/17/2018.]</ref>.
Malowicki and Shellhammer determined a calculation that predicts the isomerization rates of alpha acids into iso-alpha acids at different temperatures. Beginning at the boiling temperature of 100°C/212°F, which could be considered a rate of 100%, at 96°C/205°F the rate is 72%, and at 90°C/194°F the rate is 43%. This rate continues to drop significantly as the temperature of the wort decreases. At 82°C/180°F isomerization occurs at a rate of 17%. At a temperature of 50°C/122°F, the isomerization rate is at 1%, and finally 0% at 45°C/113°F (note that [https://www.tandfonline.com/doi/full/10.1080/03610470.2021.1878684 Kishimoto et al. (2021)] reported that isomerization begins somewhere between 60-70°C <ref name="Kishimoto_2021">[https://www.tandfonline.com/doi/full/10.1080/03610470.2021.1878684 Toru Kishimoto, Satoko Teramoto, Akiko Fujita & Osamu Yamada (2021) Evaluation of Components Contributing to the International Bitterness Unit of Wort and Beer, Journal of the American Society of Brewing Chemists, DOI: 10.1080/03610470.2021.1878684.]</ref>). This fact has several impacts on brewing processes. For example, when brewing at higher altitudes where the boiling point of wort is less than 100°C/212°F, the isomerization of alpha acids into iso-alpha acids will be reduced to whatever the rate is at that lower temperature. "Hop stands" or "whirlpool additions" where hops are left in contact with hot wort that is less than boiling temperature will continue to isomerize alpha acids <ref name="Malowicki_2005" /><ref>[https://www.mbaa.com/publications/tq/tqPastIssues/2017/Pages/TQ-54-3-0806-01.aspx A Look at Isomerization Reduction Due to Altitude. John Palmer. MBAA TQ 2017 http://dx.doi.org/10.1094/TQ-54-3-0806-01.]</ref>.
The hopping rate (weight) and IBU saturation have a drastic effect on IBU's. Aaron Justice reported a higher utilization when using Polaris hops (17.6% alpha acids) versus Tettnang hops (1.9% alpha acids). Two beers were brewed using enough of each of the hop varieties to target a calculated 40 IBU. However, the beer brewed with Polaris hops had 42.6 IBU and the beer brewed with Tettnang hops had only 28 IBU. It was hypothesized that the higher surface area of more hop matter reduces IBU's by binding to iso-alpha acids and possibly other compounds that register on the standardized IBU test. Justice also reported that more IBU pickup from whirlpooling was possible in beers without hops added in the boil, indicating that IBU saturation can limit IBU's, with a maximum IBU being around 100 <ref name="justice_2018" />.
* [http://brulosophy.com/other-projects/hop-chronicles/ Brulosophy's "The Hop Chronicles", an attempt to characterize hop flavor and aroma.]
* [https://www.hopsteiner.com/blog/blending-hops-to-match-target-hop-profile/ Hopsteiner presentation on specific blends of hops that match the flavor profile of another hop.]
===International Bitterness Unit===
Beer bitterness is often described in terms of International Bitterness Units (IBU), or more accurately, Bitterness Units (BU). The European Brewery Convention has adopted the [https://europeanbreweryconvention.eu/new-international-method-on-bitter-compounds-in-dry-hopped-beers/ “E.B.C. Bitterness Units,”] determined in a similar way and recently updated for dry hopped beers to account for humulinones, as a uniform method that best expresses the true bitter flavor value of beer <ref name="asbc_ibu">[https://www.asbcnet.org/Methods/BeerMethods/Pages/default.aspx ASBC Methods of Analysis website. Retrieved 02/11/2022.]</ref>. These measurements seek to measure the amount of iso-alpha acids, which contribute the majority of bitterness to beer. There are, however, other compounds that contribute to bitterness, such as oxidized alpha and beta acids (see [[Hops#Chemistry_and_Characteristics|Aged Hops]] below). These methods include using [https://en.wikipedia.org/wiki/Spectrophotometry spectrophotometry], [https://en.wikipedia.org/wiki/High-performance_liquid_chromatography High-Performance Liquid Chromatography-Ultraviolet (HPLC-UV)], and [https://en.wikipedia.org/wiki/Liquid_chromatography%E2%80%93mass_spectrometry liquid chromatography–mass spectroscopy (LC–MS)]. The ASBC describes these methods in depth on [https://www.asbcnet.org/Methods/BeerMethods/Pages/default.aspx their website] (see method 23; requires membership to read). While many brewers argue that the IBU measurement is not that helpful for communicating bitterness to consumers, it is generally agreed upon that IBU measurements are very useful to brewers who are seeking consistency in their products <ref>[https://beerandbrewing.com/dictionary/eej03p6ZUI/ The Oxford Companion to Beer definition of International Bitterness Units (IBUs). Retrieved 02/12/2022.]</ref>.
Compounds other than iso-alpha acids present several challenges to traditional methods of measuring BU's. Many hop compounds other than iso-alpha acids that have varying levels of perceived bitterness are detected at the same wavelength as iso-alpha acids using spectrophotometry. In addition, oxidized alpha acids are known to contribute to bitterness. As a result, updated methods of using High-Performance Liquid Chromatography-Ultraviolet (HPLC-UV) and liquid chromatography–mass spectroscopy (LC–MS) are generally recommended for measuring bitterness units in dry hopped beers (although models that account for bitterness contribution from compounds other than iso-alpha acids have not yet been completed). In addition to these challenges, iso-alpha acids and other hop compounds that contribute to bitterness degrade over time, thus the perceived bitterness of beer tends to become weaker as beer ages <ref>[https://www.chromatographyonline.com/view/liquid-chromatography-mass-spectrometry-analysis-of-hop-derived-humulone-and-isohumulone-constituents-in-beer-the-bitter-truth-of-hops-utilization-during-brewing Liquid Chromatography–Mass Spectrometry Analysis of Hop-Derived Humulone and Isohumulone Constituents in Beer: The Bitter Truth of Hops Utilization During Brewing. Bruce C. Hamper, Nicholas Viriyasiri, Aaron Boland, Lorna Espinosa, Hunter J. Campbell, Kurt Driesner, Michael McKeever. January 1, 2022. LCGC Europe, January 2022, Volume 35, Issue 01. Pages: 32–37.]</ref><ref name="asbc_ibu"/>.
Measuring BU's directly requires costly laboratory equipment, and so researchers and enthusiasts have made some progress in creating models that attempt to estimate bitterness units. These models are generally based off of boil time, alpha acid percent of the hops used, weight of the hops used, post-boil volume of wort, and gravity of the wort. These include the [http://www.realbeer.com/hops/research.html Tinseth] model, the Garetz model, and the [http://realbeer.com/hops/FAQ.html#units Rager] model. These models are often used in brewing software, such as [https://beersmith.com/blog/2021/09/23/hop-utilization-models-for-beer-brewing-compared/ BeerSmith™] and [https://www.brewersfriend.com/ibu-calculator/ Brewer's Friend]. [https://alchemyoverlord.wordpress.com/2021/11/10/ibus-and-the-smph-model/ Other models] have been proposed as potential updates to older models to address their limitations in regard to newer hopping techniques such as whirlpool hopping. Other limitations include differences in brewhouse size and efficiencies. For example, the Tinseth model was developed on a homebrew system using whole leaf hops (see the Experimental Brewing podcast interview with Glenn Tinseth link below).
See also:
* [http://scottjanish.com/dry-hopping-effect-bitterness-ibu-testing/ "Dry Hopping Effect on Bitterness and IBU Testing" by Scott Janish.]
* [https://www.experimentalbrew.com/podcast/episode-32-ibu-lie Experimental Brewing interview with Glenn Tinseth (52 minutes in).]
* [https://www.craftbeer.com/craft-beer-muses/beer-ibus-fact-fiction-misconceptions "Last Call for IBUs: Fact, Fiction and Their Impact on Your Beer," by Chris McClellan.]
==Antimicrobial Properties==
==Hop Derived Compounds In Beer and Biotransformations==
[[File:Svedlund 2022.jpg|thumb|400px|An overview of the biotransformation reactions occurring in yeast. Abbreviations: 3MH 3-mercaptohexanol, 3MHA 3-mercaptohexyl acetate, Cys cysteine, GSH glutathione, TPA terpene alcohol. Credit: Henrik Svedlund.
Source: [https://link.springer.com/article/10.1007/s00253-022-12068-w Svedlund, N., Evering, S., Gibson, B. et al. Fruits of their labour: biotransformation reactions of yeasts during brewery fermentation. Appl Microbiol Biotechnol 106, 4929–4944 (2022). https://doi.org/10.1007/s00253-022-12068-w]]]
The flavor and aroma compounds found in leaf/pellet hops are different than the hop-derived flavor and aroma compounds found in finished beer (other than in the case of dry hopping). The brewing process (particularly boiling), and fermentation greatly affect the composition of flavor and aroma compounds that are found in beer. For example, boiling wort and hops isomerizes non-bitter alpha acids into bitter iso-alpha acids. During the boiling of the wort, many compounds found in hops are evaporated, such as many of the various sulfur compounds found in hops. The terpene hydrocarbons which make up most of the hop oil content in hops (myrecene, humulene, and caryophyllene) are completely removed by fermentation. It is believed that these terpene hydrocarbons stick to the yeast cells and fall out of solution during fermentation <ref name="Praet_2012">[http://www.sciencedirect.com/science/article/pii/S1373716311001636 Biotransformations of hop-derived aroma compounds by Saccharomyces cerevisiae upon fermentation. Tatiana Praet, Filip Van Opstaele, Barbara Jaskula-Goiris, Guido Aerts, Luc De Cooman. 2012.]</ref>.
Other yeast species can also convert monoterpenes. For example, a strain of ''Kluyveromyces lactis'' was found to reduce geraniol to citronellol. This strain and a strain of ''Torulaspora delbrueckii'' produced linalool from both geraniol and nerol, and could also form geraniol from nerol <ref>[https://www.ncbi.nlm.nih.gov/pubmed/10790686 Biotransformation of monoterpene alcohols by Saccharomyces cerevisiae, Torulaspora delbrueckii and Kluyveromyces lactis. King A1, Richard Dickinson J. 2000.]</ref>. Many species of ''Debaryomyces'', ''Kluyveromyces'', and ''Pichia'' were found to transform geraniol into linalool, and nerol into linalool and alpha-terpineol <ref>[https://www.ncbi.nlm.nih.gov/pubmed/18357555 Biotransformation of acyclic monoterpenoids by Debaryomyces sp., Kluyveromyces sp., and Pichia sp. strains of environmental origin. Ponzoni C, Gasparetti C, Goretti M, Turchetti B, Pagnoni UM, Cramarossa MR, Forti L, Buzzini P. 2008.]</ref>. Colomer et al. (2020) measured the monoterpenes in two experiments before and after inoculating with different strains of ''Brettanomyces'' that had varying degrees of beta-glucosidase activity. They found that the strains with the least beta-glucosidase activity had the least impact on biotransformation, but the increase in beta-citronellol was higher than what has been reported in biotransformation studies with ''Saccharomyces'' <ref>[https://onlinelibrary.wiley.com/doi/full/10.1002/jib.610 Biotransformation of hop derived compounds by Brettanomyces yeast strains. Marc Serra Colomer, Birgitte Funch, Natalia Solodovnikova, Timothy John Hobley, Jochen Förster. 2020. DOI: https://doi.org/10.1002/jib.610.]</ref>. See [[Brettanomyces#Hop_Biotransformation|''Brettanomyces'' hop biotransformation]] for more information.
In general, different yeast strains have a large impact on how hops are perceived in the final beer, including both perceived bitterness and flavors. For example, POF+ (phenolic positive) strains of ''[[Saccharomyces|Saccharomyces cerevisiae]]'' tends to mask the hop-derived aromas in dry hopped beers <ref name="Sharp_Presentation" />. A beer hopped with the Tradition hop variety produced fruit flavors when fermented with Abbaye ale yeast, and woody/spicy flavors when fermented with US-05. When the beer was brewed with Citra hops, with US-05 the beer had sweet fruits/citrus flavors and more bitterness, but when fermented with the Abbaye ale strain the beer had a more one dimensional sweet fruit/floral flavor and less bitterness <ref>"Influence of yeast strain on hop aroma development in dry hopped beers." Christina Schönberger, Elisabeth Wiesen, Benedikt Matsche, Barth Innovations Yves Gosselin, Stephan Meulemans, Fermentis. Presentation slides at 35th Congress EBC.</ref>.
See also:
:<youtube height="200" width="300">GCQ22HSDDUQ</youtube> <youtube height="200" width="300">r09eb46k97I</youtube>
===Thiols===
Sulfur-based compounds bound to a hydrogen atom known as ''thiols'' have also been shown to be produced by yeast fermentation from the hop derived precursors cysteine or glutathione via yeast β-lyase activity. This activity takes place within the yeast cells which uptake the precursors. The cysteine and glutathione precursors are also found in malt, hops, grapes and rice, with levels varying greatly depending on varieties of the plants. In addition to some strains of ''Saccharomyces cerevisiae'' that express the genes to produce thiols, strains of the yeasts ''Metschnikowia pulcherrima'', ''Torulaspora delbrueckii'', ''Lachancea thermotolerans'', ''Candida zemplinina'', and the bacteria ''Lactobacillus plantarum'' have also been found to produce thiols <ref name="Svedlund_2022">[https://link.springer.com/article/10.1007/s00253-022-12068-w Svedlund, N., Evering, S., Gibson, B. et al. Fruits of their labour: biotransformation reactions of yeasts during brewery fermentation. Appl Microbiol Biotechnol 106, 4929–4944 (2022). https://doi.org/10.1007/s00253-022-120.]</ref>. So far, science has found that these include the volatile thiols:
* 3-mercaptohexan-1-ol (3MH; also referred to as 3-sulfanylhexan-1-ol, 3SH; ''tropical fruit'')
* 4-mercapto-4-methylpentan-2-one (4MMP; also referred to as 4-methyl-4-sulfanylpentan-2-one, 4MSP; ''blackcurrant'')
* 3-sulfanyl-4-methylpentan-1-ol (3S4MP; ''grapefruit'')
* 3-mercaptopentanol (3MP; also referred to as 3-sulfanylpentan-1-ol, 3SP)
Acetylation (acetate) variations:
* 3-sulfanyl-4-methylpentyl acetate (3S4MPA; ''passionfruit'', ''grapefruit'')
* 3-mercaptohexyl acetate (3MHA; ''passionfruit'')
Typically, in beer and wine, the amount of free thiols that are formed from these precursors is less than 1%, perhaps due to poor activity of β-lyase activity in acidic media and inhibition by polyphenols. However, these thiols were found in beers dry hopped separately with Amarillo, Hallertau Blanc, and Mosaic hop varieties. The amounts of these two thiols were higher than expected based on the content of these thiols in the hops alone <ref name="Cibaka_2016" />. Dry hopping temperature plays a role, with with 18-24°C being optimum for 3Mh and 3MP, and 28°C being optimum for 3S4MP. Mash hopping can potentially increase thiols, while using copper in the brewing or winemaking process can reduce them <ref name="Svedlund_2022" />. [[Omega Yeast Labs]] has bioengineered a yeast strain called [https://omegayeast.com/news/cosmic-punch-new-thiol-boosting-strain Cosmic Punch™ (British V OYL-011)] to produce significant amounts of thiols from hops and malted grains. [https://berkeleyyeast.com/available-yeast-strains/ Berkeley Yeast] also offers bioengineered yeast strains that produce thiols. See also this [https://www.facebook.com/groups/MilkTheFunk/permalink/1373899592638251/ MTF thread speculating on how ''Brettanomyces'' might produce thiols].
See also:
* [http://scottjanish.com/the-locksmith-utilizing-bioengineered-yeast-and-high-bound-thiol-precersour-hops-and-phantasm-powder-to-thiol-drive-beer/ "The Locksmith: Utilizing Bioengineered Yeast and High Bound Thiol Precersour Hops and Phantasm Powder to Thiol Drive Beer," by Scott Janish.]
* [http://scottjanish.com/thiol-driver/ "Thiol-Driver," by Scott Janish.]
* [https://www.charlesfaram.co.uk/news/technical-article-introduction-to-thiols-in-hop-oils/ Charles Faram Blog; Introduction to Thiols in Hop Oils.]
* [https://www.masterbrewerspodcast.com/227 IRC7 + CRISPR = Cosmic Punch - MBAA podcast with Dr. Laura Burns and Lance Shaner from Omega Yeast.]
===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 the 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>. Hops also contain polyhenols that are bound in glycosidic form that could contribute a small amount of bitterness <ref>[https://www.tandfonline.com/doi/abs/10.1080/03610470.2021.2024112?journalCode=ujbc20 Martin Biendl, Stefanie Ritter & Christina Schmidt (2022) Monitoring of Glycosidically Bound Polyphenols in Hops and Hop Products Using LC-MS/MS Technique, Journal of the American Society of Brewing Chemists, DOI: 10.1080/03610470.2021.2024112.]</ref> (see also [https://traffic.libsyn.com/secure/forcedn/thebrulab/056_Applying_the_Science_-_High_Hop_Loads_w_Jordan_Folks.mp3 Bru Lab Podcast Episode 055; Hop Bitterness And Polyphenols w/ Dr. Martin Biendl]).
The effects of beta-glucosidase on hops may be limited even in ideal conditions using pure beta-glucosidase that is highly efficient in beer where beta-glucosidase activity by yeast is limited. Sharp et al. (2017) determined that hops contain such a small amount of glycosides that their release doesn't contribute much to hop flavor and aroma. While previous studies focused on hop extracts, they studied glycosides in whole leaf hops for the first time and found non-significant levels of hop-derived monoterpenes from glycosides even when using pure beta-glucosidase extracted from almonds. For example, linalool was increased by 16.5 μg/L when using the highest hopping rate, but this amount has little impact on the overall aroma and flavor of the beer. The terpenes citronellol, terpineol, nerol, and geraniol were also not increased in significant amounts, however, 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 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. DOI: 10.1021/jf2042517.]</ref>. The alcohol 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://pubs.acs.org/doi/abs/10.1021/jf2042517 Eric G. Dennis, Robert A. Keyzers, Curtis M. Kalua, Suzanne M. Maffei, Emily L. Nicholson, and Paul K. Boss. 2012.]</ref>.
In [[lambic]] brewing, the term '''aged hops''' refers to hops (usually Noble varieties such as Tettnang, Saaz, Target, and Hallertau) which have been aged for 3-5 years in non-refrigerated conditions, and in burlap sacks or some other oxygen permeable bag <ref>[http://www.horscategoriebrewing.com/2016/04/hops-in-spontaneous-fermentation.html Dave Janssen. "Hops in spontaneous fermentation". Hors Catégorie Brewing blog. 04/28/2016. Retrieved 04/09/2018.]</ref><ref>[http://jesterkingbrewery.com/home-for-our-aged-hops "Home for Our Aged Hops". Jester King's blog. Retrieved 11/18/2016.]</ref>. It should be noted that the term "aged hops" can also refer to any sort of hop aging (especially in scientific literature), including short-term hop aging (1-6 months, for example) at refrigerated or non-refrigerated temperatures, and in oxygen-rich or vacuum sealed packaging. Much of the information below references hops that have been aged in warm conditions for shorter time periods than what hops are aged for in lambic brewing. The additional aging of hops that are used in lambic brewing or similar beers might have different effects than what has been studied in hops that are aged for shorter periods of time.
For techniques and usage amounts of aged hops, see [[Hops#Aged_Hops_in_LambicAged_Hops_in_Lambic_and_Other_Spontaneous_Fermentation_Beer|Aged Hops in Lambic]].
===Aging Hops===
[[File:Kishimoto 2021 Fig5.jpg|600px|[https://www.tandfonline.com/doi/abs/10.1080/03610470.2021.1878684 Toru Kishimoto, Satoko Teramoto, Akiko Fujita & Osamu Yamada (2021) Evaluation of Components Contributing to the International Bitterness Unit of Wort and Beer, Journal of the American Society of Brewing Chemists, DOI: 10.1080/03610470.2021.1878684.] Uploaded with permission from Toru Kishimoto.]]
It is therefore advised that brewers ask hop providers that offer aged hops what the original alpha acid percentage was when the hops were fresh, as well as the variety. This could be an important factor when determining how bitter the aged hops will taste, and potentially also how much they will negatively impact lactic acid bacteria growth. See also [[Hops#Aged_Hops_in_LambicAged_Hops_in_Lambic_and_Other_Spontaneous_Fermentation_Beer|"Aged Hops in Lambic" below]] and [https://www.facebook.com/groups/MilkTheFunk/permalink/2503097546385111 this MTF thread on IBU's from aged hops].
====Oils====
===Aged Hop Suppliers===
* [https://www.mainiacalyeastyakimachief.com/agedcommercial/hop-hops/ Mainiacal Yeast aged hops (small lots for homebrewers).]* [https://www.yakimachief.comwire/introducing-the-ych-aged-hops-program YCH offers 1-2 oz bags for homebrewers and 44 lb bags of aged hops; contact for more information.]
* <s>[http://www.hopsdirect.com/choice-debittered-aged-hops-leaf/ Hops Direct "Choice Debittered/Aged Hops" (Leaf - Cascade).]</s>
* <s>[https://hopsdirect.com/products/choice-debittered-pellets Hops Direct "Choice Debittered/Aged Hops" (Pellet - Columbus).]</s>* [https://www.freshops.com/shop/hop/aroma-hopproduct/lambic-hops/ Freshhops "Lambic Hops" (Leaf - Willamette)".]* [httphttps://www.yakimavalleyhops.com/Lambic2oz_pproducts/hopslambichops3.htm lambic-hop-pellets Yakima Valley Hops "Lambic / Aged Hops" (Pellet).]
* [http://www.farmhousebrewingsupply.com/lambic-hop-blend-4-oz-2015/ Farmhouse Brewing Supply "Lambic Hop Blend" (Pellet - Blend of varieties that are aged for ~5 years and then pelletized <ref>Private correspondence with Dustin Carver by Farmhouse Brewing Supply. 03/22/2016.</ref>).]
* [httphttps://www.themaltmiller.co.uk/index.php?_a=viewProd&productId=592 The Malt Miller (UK).]* [http:/product/www.brewstore.co.uk/specially-aged-fuggles-hops-100-grams Brew Store UK / The Malt Miller (Leaf - Fuggles).]* [http://www.brewstore.co.uk/specially-aged-hallertau-hops-100-grams Brew Store UK (Leaf - Hallertau).]
* [https://northwesthopfarms.com/products/lambic-aged-hops Northwest Hop Farms (BC, Canada).]
* [https://bsgcraftbrewing.com/lambic-hop-blend BSG sometimes offers aged pellet hops for commercial brewers; contact for details.] See [https://www.facebook.com/groups/MilkTheFunk/permalink/4326634927364688 this MTF thread] on experiences with these hops.
* [http://masterbrewerspodcast.com/098-dry-hop-creep MBAA podcast episode 98 on dry hop creep.]
* [https://brulosophy.com/podcasts/the-bru-lab/ Episode 008 | The Freshening Power Of Hops with Jake Kirkendall on the The Brü Lab podcast.]
* [https://www.onedropbrewingco.com.au/cleanfusion One Drop Brewing Co's "Clean Fusion" method of using a centrifuge to remove yeast before dry hopping in order to avoid hop creep.]
===Aged Hops in [[Lambic]] and Other [[Spontaneous Fermentation|Spontaneous Fermentation Beer]]===
[[File:Cantillon aging hops.jpg|thumbnail|right|Brasserie-Brouwerij Cantillon aging their hops; image provided by Dave Janssen.]]
Modern lambic traditionally uses aged hops at a moderate rate to help limit and select for microbes and regulate acid production. Modern Lambic brewers cite rates in the range of roughly 450 grams of hops per hectoliter of finished beer (0.6 ounces per gallon) <ref name="Jean Van Roy on Basic Brewing Radio"> [http://hwcdn.libsyn.com/p/e/a/2/ea26e00136fe1638/bbr05-30-13cantillon.mp3?c_id=5723890&expiration=1443888327&hwt=8dd886677defabdd73669cdc262ef446 Jean van Roy on Basic Brewing Radio] </ref> (~43 min in) (see also the notes pertaining hopping rates on the [[Cantillon]] page), with some brewers possibly going above this range. The age of hops used depends on the producer and their preferences/stock. Cantillon uses hops that are roughly 3 years old<ref>D. Janssen personal communication with Jean Van Roy, 9-Nov-2013</ref>, while 3 Fonteinen reports using hops that are over 10 years old<ref name="Drie Fonteinen on Belgian Smaak"> [http://www.belgiansmaak.com/armand-debelder-michael-blancquaert-drie-fonteinen/ Drie Fonteinen on Belgian Smaak] </ref> (~48 minutes in). Jester King reported using 0.66 - 0.75 pounds of whole leaf aged hops per BBL (0.34-0.39 ounces per gallon) in their spontaneously fermented ales <ref>Averie Swanson. "Sour Power! A Pro Brewer Spontaneous Fermentation Roundtable". HomebrewCon seminar. 2018.</ref> (~31:00 mins in). Lambic brewers either add their hops while still collecting wort, sometime before the wort comes to a boil<ref>[https://www.facebook.com/groups/Lambic.Info/permalink/1831338433787524/ Video of Cantillon wort reaching a boil from Bill on Lambic.info]</ref> (also known as "first wort hopping"), or shortly after boil is reached<ref name="Drie Fonteinen on Belgian Smaak"/> (~48 min in). The hops are then boiled with the wort for essentially the full length of the boil <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1593059604055581/?comment_id=1593928187302056&reply_comment_id=1593938693967672&comment_tracking=%7B%22tn%22%3A%22R9%22%7D Conversation with Dave Janssen on MTF. 02/24/2017.]</ref><ref>[http://www.lambic.info/Brewing_Lambic#Hopping "Brewing Lambic", section "Hopping". Lambic.info website. Retrieved 02/24/2017.]</ref>. The resulting lambic beers are often surprisingly bitter, especially when young. Historically, there is [http://www.horscategoriebrewing.com/2016/04/hops-in-spontaneous-fermentation.html some evidence] that lambic brewers used a combination of aged hops and fresh dried hops. Not all aged hops are the same; different varieties/sources result in different levels of residual alpha/beta acids (probably not zero), oxidized acids, IBU's, perceived bitterness, and inhibition of lactic acid bacteria. Varieties with high acids and hop oils probably have more residual acids and oils, and aging times/conditions may not be ideal enough to completely age high alpha/beta/oil hop varieties. Therefore, it is impossible to give a blanket statement on how much aged hops to use given a specific lot of aged hops. Andrew Holzhauer from Funk Factory Geuzeria suggests tasting aged hops for bitterness and adjusting the amount of hops depending on how bitter they taste <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2723907944304069/?comment_id=2723956477632549&reply_comment_id=2724104977617699&comment_tracking=%7B%22tn%22%3A%22R%22%7D Andrew Holzhauer. Milk The Funk Facebook group on how much aged hops to use. 06/13/2019.]</ref>, while James Howat from Black Project suggests making a small batch and having the wort/beer analyzed for IBU's and adjusting accordingly.
For example, homebrewer Caleb Buck performed an experiment comparing two different hopping rates for spontaneously fermented beer at home using whole leaf aged hops that were independently tested to have 0.5% alpha acids and 0.2% beta acids and were obtained from Hops Direct in Junuary 2016 <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2302073339820867/?comment_id=2302314029796798&reply_comment_id=2303737466321121 Caleb Buck. Milk the Funk Facebook group thread on Caleb's aged hop experiment. 10/01/2018.]</ref>. The two rates tested were 0.3 ounces of aged hops per gallon and 0.6 ounces per gallon, both added at the beginning of the boil <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/3970005893027595/?comment_id=3970763046285213 Caleb Buck. Milk The Funk Facebook group. Addendum to when hops were added to the boil for his associated hop experiment. 10/14/2020.] </ref>. Samples of the two worts were sent to Sweetwater Science Labs to perform IBU analysis using the ASBC standard IBU test. Interestingly, the results were 72 IBU and 127 IBU respectively. The unexpectedly high IBU might be due to the variety of aged hop, as well as oxidized hop acids showing up in the standard IBU test (see Peacock's data [[Hops#Acids_2|here that showed that aged and fresh dried hops produce a similar IBU]]). After about 7 months, one of the 0.3oz/gal batches got down to a pH of 3.6, a second batch at 0.3oz/gal got to a pH of 4, while the 0.6oz/gal batches remained within a pH of 4.2 - 4.3. From this experiment, Caleb will attempt using only 0.15 oz/gal of aged hops which should be closer to 30 IBU and so that more acidity can be achieved. James Howat from Black Project Spontaneous Ales suggests making sample wort with the hops that will be used for a larger batch and sending that sample off for IBU testing in order to more easily achieve the desired IBU's. More detail can be found on [http://www.archaicpursuit.com/2018/08/2017-coolship-experiment-hopping-rate.html?m=1 Caleb Buck's collected data on cooling rates, acidity from hopping rates, and other collected data over a multi-year, multi-batch experiment] and [http://hwcdn.libsyn.com/p/b/d/2/bd2703ec2214a5c7/bbr09-27-18souribus.mp3 Caleb's interview on this experiment on BasicBrewing Radio].
* [https://pubs.acs.org/doi/10.1021/acs.jafc.7b04055 Overview of scientific evidence of health benefits of polyphenols.]
* [https://cryopopblend.com/wp-content/uploads/2021/10/Survivable-Compounds-Handbook.pdf Survivable Compounds Handbook.]
* [https://www.youtube.com/watch?v=52nl1Fh6qnQ The hops that built craft beer – a documentary | The Craft Beer Channel.]
==References==