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Hops
,→Isomerization of Alpha Acids
==Aged Hops==
Aging hops leads to oxidation of acids and oils. Generally, brewers seek to avoid this to preserve the aromatic and bittering properties of their hops by freezing them and storing them in vacuum sealed packaging (oxygen exposure is by far the larger factor for hop degradation, followed by ambient room temperatures, which is significant because hops are often not stored in vacuum sealed packaging). However, some beer styles, including lambic and historical styles, make extensive use of aged hops. Aged hops still retain some antimicrobial properties at least partially from the formation of humulinic acids (see [[Hops#Antimicrobial_Properties|Antimicrobial Properties of Hops]]), and they can be used for microbial inhibition. In addition to their antimicrobial activity, aged hops contribute important flavor and aroma compounds and precursors to beer, while not contributing much of a strong bitterness from iso-alpha acids. These flavor descriptors often include herbal, tea-like, Earth-like, and a more dull bitterness. Low amounts of [[Isovaleric Acid]] might also contribute to the complexity of a beer that has been brewed with aged hops (although the presence of isovaleric acid in aged hops is considered temporary, and will eventually age out of hops that are aged). Historically, some brewers had issues keeping mildew from growing on aged hops that are aged in higher humidity areas (sulfur was used to combat mildew, which often gave the beer a sulfur, rotten egg aroma) <ref>[https://www.ncbi.nlm.nih.gov/pubmed/30246252?dopt=Abstract Microbial acidification, alcoholization, and aroma production during spontaneous lambic beer production. Jonas De Roos and Luc De Vuyst. 2018. DOI: 10.1002/jsfa.9291.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1228610483833830/ Conversation with Ron Smith and Aaron Barker on historical storage of hops. 02/07/2016.]</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_Lambic_and_Other_Spontaneous_Fermentation_Beer|Aged Hops in Lambic]]. ===Aging Hops===Typically, only low alpha acid hops are used (high alpha acid hops may lead to more hop character and higher inhibition of lactic acid bacteria than desired possibly due to oxidized acids). The hops are typically bound in burlap sacks/paper bags or something similar that allows for exposure to oxygen, and then they are left to age in preferably low humidity conditions at room temperatures to warm temperatures (warmer temperatures will encourage faster aging). Changes in the environment such as temperature shifts are not a concern; for example [https://web.archive.org/web/20180204131402/http://jesterkingbrewery.com/home-for-our-aged-hops Jester King Brewery in Austin Texas ages hops in a horse barn]. The hops should are traditionally aged for 2+ years. Monitor for mold growth during this time, and discard any hops that show visible signs of mold growth. Some brewers prefer to age the hops until the cheesy character ([[Isovaleric Acid]]) is gone, while other brewers do not mind the presence of this cheesy character (for example, some [[Lambic|lambic]] beers display isovaleric acid character even after packaging). While hop leaves are generally preferred over pelletized hops, if aging pellets, it has been advised to break the pellets up so that the entirety of the hop material is exposed to the air. Freshly harvested hops (also called "wet hops") should not be aged. Freshly harvested hops should be dried first, as is normal for hop processing, before aging in order to prevent [[Mold|mold]] growth (see this [https://www.canr.msu.edu/news/drying_hops_on_a_small_scale article from Michigan State University] on measuring moisture levels and [https://www.homebrewersassociation.org/how-to-brew/how-to-harvest-prepare-and-store-homegrown-hops/ this AHA article on drying hops] for home growers and this [https://www.masterbrewerspodcast.com/117 MBAA podcast interview with Val Peacock on industrial hop drying]). See also:* [https://www.facebook.com/groups/MilkTheFunk/permalink/2696660217028842/ Joshua Martinez MTF thread on using a rotary composter to pulverize pellet hops for aging.]* [https://www.facebook.com/groups/MilkTheFunk/permalink/3042350479126479/ MTF thread on general tips on aging hops.] ===Chemistry and Characteristics===During aging and if exposed to oxygen, compounds in hops oxidize into different compounds known collectively as "oxidative polar compounds" or OPC's. Hao et al. (2020) reported 39 different OPC's in aged hops, with 15 of them derived from alpha acids, 15 derived from isomerized alpha acids, and 9 from beta-acids <ref name="Hao_2020" />. Many of these oxidation derived compounds are considered "hard resins" (meaning they are soluable in alcohol) and contribute bitterness and antimicrobial properties to beer. Examples of "soft resins", which are not soluable in alcohol, are alpha and beta acids <ref name="Almaguer_2015">[https://onlinelibrary.wiley.com/doi/full/10.1002/jib.160 Almaguer, C., Schönberger, C., Gastl, M., Arendt, E. K. and Becker, T. (2014), Humulus lupulus – a story that begs to be told. A review, J. Inst. Brew., 120: 289– 314. DOI: 10.1002/jib.160.]</ref>. ====Summary of Oxidized Hop Acids==== {| class="wikitable sortable" style="width:75%;"|-| colspan="5" align="center" style="padding: 2em;" | '''Alpha Acid Derived Compounds <ref name="Hao_2020" />'''|- ! Oxidized Compound ! Precursor ! Beer Soluble (Y/N/?) ! Bitterness Level ! Notes|-| Humulinones (cohumulinone, n-humulinone, and adhumulinone) || Alpha acids (cohumulone, humulone, and adhumulone) || Y || 66% as bitter as iso-alpha-acids || In hops, alpha-acids are degraded to humulinones in the presence of air, with higher temperatures leading to more rapid conversion. |-| tricyclooxyisohumulones A and B, deisopropyltricycloisohumulone, and tricycloperoxyisohumulone A || Alpha acids || ? || ? || Along with humulinones and 4'-hydroxy-allohumulinones, they are considered aging indicators of of hop oxidation.|-| Abeo-isohumulone || Humulinone || ? || Not reported; might contribute to bitterness of beers with high amounts of aged hops. || Derived from the oxidation of humulinone in hops. Found in naturally aged Saaz and Nugget hops over a long period of storage. |-| 4'-hydroxy-allohumulinones || Humulinones || ? || Not reported; might contribute to bitterness of beers with high amounts of aged hops. || Believed to be derived from the oxidation of humulinone in hops. They are more stable than humulinone over time and are thus thought to be useful indicators of the degree of oxidation in hops.|-| 4'-Hydroxyallo-cis-humulinones and cis-oxyhumulinic acids || 4'-hydroxy-allohumulinones || Y || Contributes to bitterness quality || These are formed during boiling where 4'-hydroxy-allohumulinones are isomerized into 4'-Hydroxyallo-cis-humulinones for the first 60 minutes of boiling, and then the 4'-Hydroxyallo-cis-humulinones are slowly degraded into cis-oxyhumulinic acids after 60 minutes of boiling. After 120 minutes of boiling, 40-50% of the 4'-hydroxy-allohumulinones is transformed into 4'-Hydroxyallo-cis-humulinones and cis-oxyhumulinic acids. These are thought to effect the bitterness quality of beer, and as hard resins they could help improve head retention <ref>[https://www.researchgate.net/publication/286063120_Contributions_of_hop_hard_resins_to_beer_quality Almaguer, Cynthia & Gastl, Martina & Arendt, Elke & Becker, Th. (2012). Contributions of hop hard resins to beer quality. BrewingScience. 65. 118-129.]</ref>.|-| Scorpiohumulinols A/B and dicyclohumulinols A/B || 4'-hydroxy-allohumulinones || ? || ? || Potentially makes up the majority (70%) of compounds derived from the degradation of 4'-Hydroxyallo-cis-humulinones in beer stored at 40°C over 12 weeks.|-| colspan="5" align="center" align="center" style="padding: 2em;" | '''Beta Acid Derived Compounds <ref name="Hao_2020" />'''|-! Oxidized Compound !! Precursor !! Beer Soluble (Y/N/?) !! Bitterness Level !! Notes|-| Hulupones (cohulupone, hulupone) || Beta acids (colupulone, lupulone) || Y || 84% as bitter as iso-alpha-acids (short-lasting alpha-acid-like bitterness); colupulone has a flavor threshold of 7.9 umol/L || Degradation rate of beta acids into hulupones increases with temperature. Has a relatively low absorption in wort (4.8–10.4%). May also degrade into other unknown compounds other than hulupinic acids.|-| Hulupinic Acids || Hulupones || Y || Contributes marginal bitterness to beer; flavor threshold of 69 umol/L || Has a relatively low degradation in wort.|-| Tricyclocolupone epimers A/B || Beta acids (colupulone) || Y || Contributes long-lasting lingering and harsh bitterness; flavor threshold of 38-54 umol/L || Found to survive the brewing process up to 50% in a Pilsner style beer.|-| Dehydrotricyclocolupones epimers A/B || Beta acids (colupulone) || Y || Contributes long-lasting lingering and harsh bitterness; flavor threshold of 40 umol/L || Found to not survive the brewing process in a Pilsner style beer, so it might not contribute to beer bitterness.|-| Hydroperoxy-tricyclocolupone epimers A/B || Beta acids (colupulone) || Y || Contributes long-lasting lingering and harsh bitterness; flavor threshold of 20 umol/L || Found to not survive the brewing process in a Pilsner style beer, so it might not contribute to beer bitterness.|-| Hydroxy-tricyclocolupone epimers A/B || Beta acids (colupulone) || Y || Contributes long-lasting lingering and harsh bitterness; flavor threshold of 14-17 umol/L || Found to not survive the brewing process in a Pilsner style beer, so it might not contribute to beer bitterness.|-| Nortricyclocolupone || Beta acids (colupulone) || Y || Contributes bitterness; flavor threshold of 90 umol/L || Found to survive the brewing process.|-| Epoxycohulupone and Epoxyhulupon || Beta acids (colupulone, lupulone) || ? || ? || Newly discovered; not much is known about them.|-| colspan="5" align="center" align="center" style="padding: 2em;" | '''Iso-Alpha Acid Derived Compounds <ref name="Hao_2020" />'''|-! Oxidized Compound !! Precursor !! Beer Soluble (Y/N/?) !! Bitterness Level !! Notes|-| ''cis''-alloisohumulone and ''trans''-alloisohumulone || Iso-alpha acids (''cis''-isohumulone and ''trans''-isohumulone) || Y || ? || ''cis''-alloisohumulone was found in trace levels in a Pilsner style beer at all different aging points, but ''trans''-alloisohumulone remained undetected.|- | ''trans''-humulinic acid and ''cis''-humulinic acid || Iso-alpha acids (''cis''-isohumulone and ''trans''-isohumulone) || Y || No bitterness || Minor levels in wort, but stable through the brewing process. Higher levels were detected in beers aged in oxygen permeable PET bottles versus glass bottles. Humulinic acid content increases over the storage of beer over many years as iso-alpha acids decrease. It has been suggested that the decomposition of iso-alpha acids into humulinic acids over time plays a role in the decrease in perceived bitterness of aged beer. |-| Hydroperoxy-''cis''-alloisohumulones and Hydroperoxy-''trans''-alloisohumulones || Iso-alpha acids (''cis''-isohumulone and ''trans''-isohumulone) || Y || ? || Iso-alpha acids degrade into these in beer that is exposed to oxygen after just 1-2 hours. ''Cis''-isohumulone degrade into hydroperoxy-''cis''-alloisohumulones, while ''trans''-isohumulone degrade into Hydroperoxy-''trans''-alloisohumulones and tricyclohumol. They are also formed during the wort boiling process, but are reduced by 50% during the fermentation process. Hydroperoxy-''trans''-alloisocohumulone increases as beer is stored in bottles over many years (1, 4, and 10 years were measured in one study), while hydroperoxy-''cis''-alloisocohumulone is less stable and decreases. In PET bottles, both types of hydroperoxy-alloisohumulones decreased to zero after 4 years of storage at room temperature. While the degredation of iso-alpha acids into hydroperoxy-alloisohumulones occurs very quickly when in the presence of oxygen, the degradation of hydroperoxy-alloisohumulones occurs much more slowly during storage at room temperature.|-| Hydroxyl-''cis''-alloisohumulones and Hydroxyl-''trans''-alloisohumulones || Hydroperoxy-''cis''-alloisohumulones and Hydroperoxy-''trans''-alloisohumulones || Y || ? || Hydroperoxy-alloisohumulones are further degraded into their respective hydroxyl-alloisohumulones (''cis'' and ''trans'') via metal ions or UV light. Similar to hydroperoxy-alloisohumulones, hydroxyl-''trans''-alloisohumulones slowly increase during storage of bottles at room temperature over many years (1, 4, and 10 years), while hydroxyl-''cis''-alloisohumulones slowly decrease. In PET bottles, both types degrade to nearly 0 (from 0.39 umol/L to 0.08 umol/L) after 4 years at room temperature. When beer is intentionally oxidized, the hydroperoxy-alloisohumulones degrade very quickly over 24 hours into their hydroxyl-alloisohumulones derivatives.|-| Tricyclohumulactol || Hydroperoxy-alloisohumulones || Y || ? || Only detected in a model solution; not detected in fresh or aged beer possibly due to low concentrations and/or coelution with isobaric molecules, exposing a technical difficulty of detecting these compounds in beer.|-| Scorpiohumols || Hydroxyl-''trans''-alloisohumulone || Y || ? || Same as Tricyclohumulactol.|-| Tricyclocohumol, Tricyclocohumene, Isotricyclocohumene, Tetracyclocohumol, and Eptitetracyclocohumol || ''Trans''-isohumulone (iso-alpha acid) || Y || Bitterness thresholds in beer as umol/L: 30, 5, 10, 70, 70 (''Trans''-isohumulone is 20). Characterized as "lingering harsh bitterness". || The most abundant oxidation derived hop compounds in aged beer. All are derived from ''trans''-isohumulone, which is the iso-alpha acid that is less stable than ''cis''-isohumulone. ''Trans''-isohumulone degrades into these faster at warmer temperatures and lower pH (no degradation at a pH of 6, slower degradation at a pH of 3, and very fast degradation at a pH of 1). Even differences as small as 0.1 pH (4.2, 4.3, and 4.4 pH values were tested) can make a significant difference in the degradation rate of ''trans''-isohumulone into tricyclocohumol, with lower pH values leading to faster degradation. After storing beer in brown bottles at 28°C for 8 months, these degradation products were detected at high amounts. Tricyclohumol remains relatively stable, even in the presence of oxygen.|- |} ====Acids====During aging, both alpha and beta acids oxidize and degrade with warmer temperatures and more oxygen exposure having a greater impact. The generally accepted theory is that oxygen interacts directly with hop acids. This event is called "autooxidation". An alternative theory to this is that oxygen indirectly oxidizes acids by first oxidizing the hop oils and turning them into pro-oxidants, which then oxidize the hop acids which are mixed in with the oils within the lupulin glands <ref name="Algazzali_2014" />. The oxidation of hop acids corresponds with an increase in the [http://methods.asbcnet.org/summaries/hops-12.aspx Hop Storage Index (HSI)], which is a practical way of measuring the overall freshness of hops. As the oxidation of hop oils rises, the measured HSI number on a lot of hops increases <ref name="Lam et al., 1986"/><ref name="Maye_2016">[http://www.hopsteiner.com/wp-content/uploads/2016/07/TQ-53-1-0227-01.pdf Humulinone Formation in Hops and Hop Pellets and Its Implications for Dry Hopped Beers. John Paul Maye, Robert Smith, and Jeremy Leker. 2016.]</ref>. These oxidized compounds lead to a higher amount of non-alpha-acid bitterness compounds in aged hops and have a remarkable effect on the bitterness of the beer. The bitterness from oxidized hop compounds has been described as more earthy, harsh, and astringent than the sharper, cleaner bitterness from iso-alpha acids <ref name="Mikyška_2012">[http://onlinelibrary.wiley.com/doi/10.1002/jib.40/abstract Assessment of changes in hop resins and polyphenols during long-term storage. Alexandr Mikyška and Karel Krofta. 2012.]</ref>. Aging hops while exposed to oxygen develops a cheesy aroma due to [[Isovaleric Acid|isovaleric acid]], isobutyric acid, and 2-methylbutyric acid. These acids are produced by the oxidative cleavage of acyl side chains of the hop resins <ref name="Briggs_2004" />. These cheesy oxidation compounds can be esterified to form wine-like and fruity tasting compounds (see [[Hops#Esters|Esters]] below and [[Aging_and_Storage#Acids_and_Esters|Aging and Storage]]) <ref name="Shellhammer, Vollmer and Sharp, CBC 2015"/>. Storage conditions and variety play a large role in how acid content in hops changes over time. Beta acids are generally more resistant to oxidation than alpha acids. A study by Mikyška and Krofta (2012) found that after 12 months of storage at 20°C in open air, pellet hops lost 64-88% of their alpha acid content and 51-83% of the beta acid content, with the beta acids dropping off more significantly after 6 months (alpha acid content declined steadily throughout the aging period). These amounts varied with different Czech hop varieties (Saaz, Sládek, Premiant, and Agnus), and beta acids degraded slower than alpha acids as seen below <ref name="Mikyška_2012" /> (percentages listed below are how much percent was lost): {| class="wikitable sortable"|-! Storage !! Oil !! Hallertau Magnum (Pellet, 14% AA) <ref name="Kishimoto_2021" /> !! Saaz (Pellet) <ref name="Mikyška_2012" /> !! Sládek (Pellet) <ref name="Mikyška_2012" /> !! Premiant (Pellet) <ref name="Mikyška_2012" /> !! Agnus (Pellet) <ref name="Mikyška_2012" /> !! Saaz (Leaf) <ref name="krofta_2013">[http://www.actahort.org/books/1010/1010_26.htm Stability of Hop Beta Acids and Their Decomposition Products during Natural Ageing. K. Krofta, S. Vrabcová, A. Mikyska, M. Jurková, T. Cajka , J. Hajslová. 2013.]</ref> !! Vital (Leaf) <ref name="krofta_2013" /> !! Pure Beta Acid <ref name="krofta_2013" /> |-| colspan="10" | '''Open air at 20°C for 12 months'''|- align="right"| || Alpha acids || || -80% || -88.3% || -64.3% || -78.2% || || |- align="right"| || Beta acids || || -60.5% || -83% || -53.7% || -51% || -50% || -77.5% || -99%|- | colspan="10" | '''Open air at 40°C for 3 months'''|- align="right"| || Alpha acids || -100% || || || || || || |||- | colspan="10" | '''Vacuum sealed at 20°C for 12 months'''|- align="right"| || Alpha acids || || -20.6% || -24.9% || -22.2% || -21.7% || || |||- align="right"| || Beta acids || || -2.7% || -1.7% || -2.1% || -1.2% || || |||-| colspan="10" | '''Vacuum sealed at 2°C for 12 months'''|- align="right"| || Alpha acids || || -1.1% || -5.5% || -0.3% || -1.4% || || |||- align="right"| || Beta acids || || -1.7% || -2.3% || -0.4% || -0.5% || || |||-|} It has been established that many factors influence the initial content of alpha and beta acids, such as cultivar (variety), cultivation area, climate and environmental conditions, harvest year, and harvest date. For example, early harvest dates result in hop cones that are not fully developed and contain less alpha/beta acids, and late harvest dates can produce hop cones with lower alpha/beta acids as these acids begin to degrade. Thus, optimal harvest dates occur when the hop cones reach their maximum size but before they become brittle and hop acid degradation begins. [https://www.pja.iung.pulawy.pl/stability-of-the-hop-bitter-acids-during-long-term-storage-of-cones/ Skomra and Koziara-Ciupa (2020)] found that harvest date also affects how alpha and beta acids degrade over time during storage. They looked at alpha and beta acid degradation differences for 4 varieties of hops grown at the same farm, but harvest at 3-4 different dates (7-10 days between harvest dates) <ref name="Skomra_2020">[https://www.pja.iung.pulawy.pl/stability-of-the-hop-bitter-acids-during-long-term-storage-of-cones/ Stability of the hop bitter acids during long-term storage of cones with different maturity degree. Urszula Skomra, Marta Koziara-Ciupa. Polish Journal of Agronomy 2020, 40, 16–24. DOI: 10.26114/pja.iung.406.2020.40.03.]</ref>. The hops were stored at 5°C and 20°C in aerobic conditions for 12 months <ref>Private correspondence with Urszula Skomra by Dan Pixley. 07/21/2020.]</ref>. As expected, the lower storage temperature of 5°C preserved the alpha and beta acids better than the warmer 20°C storage temperature. In general, an earlier harvest date also resulted in greater degradation of alpha and beta acids, but there were some exceptions to this. For example, Sybilla Harvest Date II produced the most stable alpha acid content (harvesting too early or too late resulted in less stable alpha acid content), while for Magnet Harvest Date II resulted in the most degradation of alpha and beta acids and Harvest Date III was preferable for alpha acid stability. In general, the stability of beta acids depended more on the harvest date than the stability of alpha acids <ref name="Skomra_2020" />. See the table below. Skomra and Koziara-Ciupa (2020) also reported that for the first 3 to 6 months, the alpha and beta acids were relatively stable. The cooler storage had a longer period of initial stability than the warmer storage. After the initial period of stability, the alpha and beta acids began a rapid drop around 9 months of total storage. From 9-12 months, the rate of decline in alpha and beta acids was much slower and seemed to somewhat stabilize <ref name="Skomra_2020" />. {| class="wikitable sortable"|-! Storage !! Oil !! Sybilla (Leaf) <ref name="Skomra_2020" /> !! Puławski (Leaf) <ref name="Skomra_2020" /> !! Magnat (Leaf) <ref name="Skomra_2020" /> !! Magnum (Leaf) <ref name="Skomra_2020" /> |-| colspan="9" | '''Open air at 5°C for 12 months''' (Harvest dates I, II, II, and only for Magnat/Magnum IV)|-| || Alpha acids || -10.8%, -4.5%, -7.9% || -11.0%, -6.4%, -6.8% || -25.8%, -40.8%, -2.3%, -9.3% || -17.7%, -4.5%, -12.9%, -11.2% |-| || Beta acids || -7.6%, -6.3%, -8.5% || -28.1%, -10.9%, -17% || -33.3%, -37.2%, -21.1%, -22.3% || -28.1%, -7.6%, -3.9%, -5.2% |-| colspan="9" | '''Open air at 20°C for 12 months''' (Harvest dates I, II, II, and only for Magnat/Magnum IV)|-| || Alpha acids || -28.5%, -11.3%, -27.1% || -18.6%, -35.3%, -37.6% || -35.4%, -56.8%, -31.7%, -36% || -38.3%, -25.7%, -28.9%, -24.4% |-| || Beta acids || -26.4%, -38.6%, -49.5% || -43.3%, 45.7%, 54.1% || -46.3%, -66.6%, -59.8%, -59.2% || -53.7%, -28.1%, -16.8%, -19.9%|-|} '''Oxidized alpha acids''' (humulinones) are similar in taste perception to iso-α-acids, but have been described as less bitter (an average of about 66% as bitter on a 1 to 1 basis). The quality of the bitterness from oxidized alpha acids has been described in one study as "smoother and less lingering" than iso-alpha acids; this was attributed to humulinones being more polar than iso-alpha acids and therefore do not stick or linger on the tongue as long as iso-alpha acids <ref name="Shellhammer, Vollmer and Sharp, CBC 2015"/><ref name="Maye_2016" />. While the taste threshold of iso-alpha acids is 5-6 mg/L in light lager, the threshold for humulinones has been measured to be 8 mg/L in light lager (note that this is an average; tasters vary widely in how much bitterness they perceived from different bitter compounds) <ref name="Algazzali_2014" />. Humulinone content increases in hops after being pelletized (whole leaf hops have less humulinones). In fresh pellet hops that have a relatively low humulinone content, the humulinones contribute little to the bitterness of the beer when boiled, however when dry hopped they readily dissolve into the beer and have a significant impact on the beer's bitterness. With heavy dry hopping, the humulinones also decrease iso-alpha acid content of beer with more than about 25 IBU's, but not in beer with less than about 20 IBU. The decrease in iso-alpha acids and perceived bitterness/IBU is partially made up for the bitterness of the humulinones themselves (humulinones are picked up in IBU measurements with a [http://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Kinetics/Reaction_Rates/Experimental_Determination_of_Kinetcs/Spectrophotometry spectrophotometer] and as such it has been suggested that IBU's be [http://masterbrewerspodcast.com/004-dry-hopping-its-effects-on-bitterness-and-the-ibu-test-0 measured more accurately with HPLC]). In beers with less than 20 IBU, high dry hopping rates greatly increase the bitterness/IBU due to the bitter humulinones <ref name="Maye_2016" />. Humulinones also increase foam creation and stability by binding with the foam positive protein, Protein Z, via hydrogen bonding <ref>[https://www.sciencedirect.com/science/article/abs/pii/S0308814623020678 Chen Xu, Xuanqi Zhang, Mingyang Sun, Hanhan Liu, Chenyan Lv. Interactions between humulinone derived from aged hops and protein Z enhance the foamability and foam stability. Food Chemistry, Volume 434, 2024, 137449, ISSN 0308-8146, https://doi.org/10.1016/j.foodchem.2023.137449.</ref>. The rate of humulinone formation is limiting. Maye et al. (2016) showed that humulinone formation occurred rapidly during hop pelletization, and the concentration peaks during this time (these researchers found that further exposure to air did not increase humulinone content). They speculated that this is because when whole leaf hops are baled, only 20% of lupulin glands are broken, whereas when they are pelletized 100% of the lupulin glands are broken. In contrast, Taniguchi et al. (2013) found that humulinone formed slowly over 40 weeks in pellets that were stored at 20°C, but at 40°C and 60°C storage temperature they formed quickly and then diminished to very low levels at 10 weeks and 2 weeks respective to the higher storage temperatures. This demonstrated that warm storage increases the rate of humulinone formation. In addition, the oxidized hop compound 4′-hydroxy-allohumulinone increased trailing behind the humulinone formation and at a similar concentration at 20°C over 40 weeks of storage, and were much more stable than humulinones when stored at 40-60°C for 40 weeks <ref>[https://pubs.acs.org/doi/10.1021/jf3047187 Identification and Quantification of the Oxidation Products Derived from α-Acids and β-Acids During Storage of Hops (Humulus lupulus L.). Yoshimasa Taniguchi, Yasuko Matsukura, Hiromi Ozaki, Koichi Nishimura, and Kazutoshi Shindo. Journal of Agricultural and Food Chemistry 2013 61 (12), 3121-3130. DOI: 10.1021/jf3047187.]</ref>. The exact mechanism by which alpha acids are converted to humulinones is not known. The amount of humulinone correlates strongly with the [http://methods.asbcnet.org/summaries/hops-12.aspx Hop Storage Index (HSI)] <ref name="Maye_2016" />. Humulinone content in long-aged hops (1+ years) has not been studied. '''Oxidized beta acids''' produce some compounds that also contribute to the perception of bitterness, specifically hulupones. Unlike humulinones which form relatively quickly from the oxidation of alpha acids, hulupones form at a much slower rate <ref name="Dušek_2014" />. Also unlike humulinones, they survive boiling and fermentation. While some sensory analysis of beers containing oxidized beta acids describes the resulting bitterness as "harsh and clinging", another analysis by Krafta et al (2013) described the bitterness of oxidized beta acids in beer when added in their pure form at the beginning of the boil as "pleasant and not lingering". The more degradation of beta acids into oxidized beta acids that occurs in hops, the more bitter beers brewed with these hops will be <ref name="krofta_2013" />. Two other compounds other than hulupones have been identified as being produced by the oxidation of beta acids, epoxycohulupone and epoxyhulupone. Their effect on beer flavor is not yet known; however, it is believed that hulupones have a greater impact on beer flavor and bitterness than these compounds <ref name="Dušek_2014" />. The bitterness of hulupones has received some debate among researchers. In 1973, a researcher found that hulupones are about 50% as bitter as iso-alpha acids. Briggs et al stated the complete opposite, and that hulupones are twice as bitter as iso-alpha acids. More recent studies using modern analysis techniques found that on a weight for weight basis, hulupones are 35-40% as bitter as iso-alpha acids in one study, and another found that they were 84% (+/- 10%) as bitter as iso-alpha acids (note that this is an average; tasters vary widely in how much bitterness they perceived from different bitter compounds) <ref>[https://www.researchgate.net/publication/307796892_The_effect_of_hop_beta_acids_oxidation_products_on_beer_bitterness The effect of hop beta acids oxidation products on beer bitterness. Karel Krofta, Světlana VRABCOVÁ, Alexandr Mikyška, and Marie JURKOVÁ. 2013.]</ref><ref name="Algazzali_2014" /><ref name="Briggs_2004">[https://www.crcpress.com/Brewing-Science-and-Practice/Briggs-Boulton-Brookes-Stevens/p/book/9780849325472 Brewing Science and Practice. Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes, Roger Stevens. 2004.]</ref>. While the taste threshold of iso-alpha acids is 5-6 mg/L in light lager, the threshold for hulupones has been measured to be 7-8 mg/L in light lager <ref name="Algazzali_2014" />. Both humulinones and hulupones have been identified as forming due to the oxidation of hop acids. However, other researchers have reported that both of these bitter compounds formed during the boiling of hops, and another during the storage and aging of beer. In all cases, the amounts of the compounds directly correlated with the amount of hops used <ref name="Algazzali_2014" />. Other compounds have been associated with the oxidation of beta acids and are extracted during wort boiling. These are described as giving a long-lasting, lingering bitterness on the palate. They include hydroxytricyclo-lupulone, dehydrotricyklolupulone, and hydroperoxytricyklolupulone <ref>[http://www.sciencedirect.com/science/article/pii/S0308814609001770 Structure determination and sensory evaluation of novel bitter compounds formed from β-acids of hop (Humulus lupulus L.) upon wort boiling. Gesa Haseleu, Daniel Intelmann, Thomas Hofmann. 2009.]</ref>. ====IBU==== The overall effect of oxidized compounds in aged hops has been shown by Val Peacock, a former scientist at Anheuser-Busch. Peacock stored hops at four different temperatures for 18 months. His data showed that although the alpha acid content in the hops and the iso-alpha acid content in the beers brewed with them decreased the older the hops were stored, the measured IBU of the different beers was about the same. This is because the oxidized acids in hops show up in the same spectrum as iso-alpha acids when using the ASBC method of measuring IBUs with a spectrophotometer <ref name="Aron">[https://www.homebrewersassociation.org/how-to-brew/resources/conference-seminars Dr. Patricia Aron. "Bitterness and the IBU: What’s It All About?" HomebrewCon 2017 Presentation. ~34 mins in. Retrieved 09/05/2017.]</ref>. This data is shown below. Caleb Buck's experiment [[Hops#Aged_Hops_in_Lambic|seen below]] supports this. Although it has not been shown that oxidized alpha and/or beta acids can inhibit lactic acid bacteria, if they do, then this might help explain reports <ref>[https://homebrewingfun.blogspot.com/2019/11/one-gallon-spontaneous-fermentation.html Adam Kielich. "One Gallon Spontaneous Fermentation Beer Batch 5 Recipe and Brewday". Brain Sparging on Brewing. 11/16/2019.]</ref> of using aged hops that originally had a high alpha acid content retaining a strong inhibitory effect towards lactic acid bacteria. {| class="wikitable sortable"|-! Storage Temperature <ref name="Aron" /> !! Alpha Acid in Hops !! Iso-Alpha Acids in Beer !! Beer IBUs|-| -15°F || 3.2% || 19.8 ppm || 13.5|-| 25°F || 2.91% || 18.1 ppm || 12.0|-| 45°F || 1.71% || 14.4 ppm || 13.5|-| 70°F || 0.41% || 2.9 ppm || 11.0|} [https://www.tandfonline.com/doi/full/10.1080/03610470.2021.1878684 Kishimoto et al. (2021)] reported similar results when making beers with forcibly aged hops. They aged Magnum hop pellets (14% AA) at 40°C and exposed to air for a number of different days: 3, 5, 7, 10, 14, 21, 30, and 90 days. The hops aged for 14 days had 9.8% AA, 21 days had 4.4% AA, 30 days had 1.2% AA, and 90 days had 0% AA. The IBU (measured with a spectrophotometer using Method Beer-23A from the American Society of Brewing Chemists) for the different beers made with the aged hops was more or less the same despite how much alpha acids were left in the aged hops. However, beers brewed with the different aged hops reflected a rapid decrease in iso-alpha acids in the beers made with the aged hops. Perceived bitterness also decreased for the beers made with the aged hops, but not as much as the decrease in ppm of iso-alpha acids, again demonstrating the oxidized hop compounds carry some bitterness, but less bitterness than iso-alpha acids <ref name="Kishimoto_2021" />. See Figure 5 from Kishimoto et al. (2021): [[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_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====[[File:Lam Hop Oils.jpg|thumb|400|[http://pubs.acs.org/doi/pdf/10.1021/jf00070a043 Data from "Aging of hops and their contribution to beer flavor" by Kai C. Lam, Robert T. Foster and Max L. Deinzer.] '''Aged I''': 2 weeks at 90°F; '''Aged II''': 60 additional days at 90°F.]] Hop oils also generally degrade over time, however, their degradation rates are more complex. [http://pubs.acs.org/doi/abs/10.1021/jf00070a043 Lam et al. (1986)] found that aging both cascade and North American grown Hallertauer Mittelfrueh resulted in an increase in grapefruit-like character, although the compound that caused this was not identified. In the case of Cascade the intensity of this flavor correlated with the age of the hops <ref name="Lam et al., 1986"> [http://pubs.acs.org/doi/abs/10.1021/jf00070a043 Aging of Hops and Their Contribution to Beer Flavor. Lam et al. 1986.] </ref>. In the Hallertauer hops, aging resulted in an increase in a spicy/herbal character <ref name="Lam et al., 1986"/>, which is in agreement with reports of oxidized sesquiterpenes (specifically humulenol II, humulene diepoxides, caryophyllene, and to a lesser extent humulene monoepoxides and alpha-humulene) contributing a spicy/herbal flavor to beer <ref name="Goiris et al., 2002">[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2002.tb00129.x/abstract Goiris et al., 2002]</ref><ref name="Mikyška_2012" />. Many of the oils followed in the Lam et al. (1986) study which increased during a short accelerated aging period (2 weeks at 90°F) then decreased during extended aging (60 additional days at 90°F). The cascade hops lost more of the fruity/citrusy hop oils (myrecene, linalool, and geranial) than Hallertauer, suggesting that different strains of hops can withstand aging better than others. The concentration of hop oils are affected by the brewing process and fermentation (see the table) <ref name="Lam et al., 1986"/>. Another study found that beta-ionone (classified as a ketone, and characterized as "floral" and "woody" <ref>[http://www.thegoodscentscompany.com/data/rw1006632.html Beta-ionone. Good Scents Company. Retrieved 11/22/2016.]</ref>) increased in beers brewed with hops that were aged for 30 days at 40°C versus beers brewed with aged hops <ref name="kishimoto_2007" />. A 2017 study at the Shellhammer lab looked at how trained panelists and consumers perceived a lager beer dry hopped with slightly oxidized Hallertau Mittelfrüh hops (exposed to oxygen once, then stored at 38°C for two weeks) versus highly oxidized (daily exposure to oxygen and stored at 38°C for two weeks). They found that the trained panelists detected more characteristics that are associated with noble hops; e.g. more woody, earthy, and herbal characteristics in the lager beers dry hopped with oxidized hops. They also found the oxidized hopped beers to be more bitter (probably due to oxidized alpha and beta acids). Consumers were not statistically able to tell the difference. The study determined that oxidized hops might serve to provide nuanced increases in noble hop character <ref>[http://www.asbcnet.org/publications/journal/vol/2017/Pages/ASBCJ-2017-1287-01.aspx Aroma Properties of Lager Beer Dry-Hopped with Oxidized Hops. Daniel M. Vollmer, Victor Algazzali, and Thomas H. Shellhammer. 2017.]</ref>. In a similar study by Hengyuan et al. (2023), aging Saaz hops for a short amount of time (aged at 30 ℃ in a ventilated environment for 5 days) reduced the grassy and resinous character and improved the spicy and woody character of single hopped beers (hopped at three points in the boil and dry hopped). Consumers also preferred this beer over the other samples, including fresh Saaz. However, over-aging Saaz hops resulted in less preference with consumers (30 ℃ for 10 days, 40 ℃ for 5 days, or 40 ℃ for 10 days). This effect was not demonstrated by Simcoe hops, however, indicating that short aging is only beneficial for some hop varieties. Under the same aging condition with Simcoe hops, consumers preferred the fresh Simcoe, and any degree of aged Simcoe was less preferred. The beers with aged Simcoe hops were described as having less fruity and floral character and more dry, thin bitterness <ref>[https://www.bio-conferences.org/articles/bioconf/abs/2023/04/bioconf_icbb2023_01016/bioconf_icbb2023_01016.html Aging of Hops and Their Effects on India Pale Ale Flavor. Hengyuan Xu, Shaokang Sun, Xiaochen Wang, Haojun Zhang and Cong Nie. BIO Web Conf., 59 (2023) 01016. DOI: https://doi.org/10.1051/bioconf/20235901016.]</ref>.
* [http://scottjanish.com/increasing-bitterness-dry-hopping/ "Increasing Bitterness By Dry Hopping", article by Scott Janish on oxidized alpha acids.]
* [https://beerandbrewing.com/dictionary/Bu1Rco6Cpn/hulupones/ Hulupones - oxidized beta acids.]
====Polyphenols====
Polyphenols, including [https://en.wikipedia.org/wiki/Flavonoid polyphenol flavanoids], also degrade in hops as they age. However, storage conditions have less of an impact on the degradation of polyphenols compared to alpha and beta acids. Mikyška and Krofta (2012) found that regardless of how the hops were stored polyphenols started to decay after about 6 months and after 12 months aged hops lost about 30-40% of polyphenols and 20-30% of flavanoids <ref name="Mikyška_2012" />.
====Esters====
During fermentation, it is believed that esters are produced by yeast metabolism from hop compounds such as alpha acids, beta acids, polyphenols, and hydrocarbons because they are not found in unhopped beer or in hops themselves. These esters include ethyl 2-methylpropanoate (citrus, pineapple, sweetness), ethyl 2-methylbutanoate (citrus, apple-like), ethyl 3-methylbutanoate (citrus, sweetness, apple-like), 2-phenylethyl 3-methylbutanoate (floral, minty), and 4-(4-hydroxyphenyl)-2-butanone (citrus, raspberry) <ref>[http://pubs.acs.org/doi/abs/10.1021/jf061342c Comparison of the Odor-Active Compounds in Unhopped Beer and Beers Hopped with Different Hop Varieties. Toru Kishimoto, Akira Wanikawa, Katsunori Kono, and Kazunori Shibata. 2006.]</ref>. [https://researchmap.jp/?action=cv_download_main&upload_id=110987 Kishimoto et al.] found that some beer esters were increased when using unidentified pellet hops (described in the study only as "a bitter variety of 11.5% alpha acid") that were aged for 30 days at 40°C versus using fresh pellet hops that were stored cold (4°C). Specifically, in the beers that used the aged hops, they found a significant increase in citrus esters (ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, and 4-(4-hydroxyphenyl)-2-butanone), and a decrease in "green, hop-pellet-like, and resinous" compounds such as myrcene and (Z)-3-hexen-1-ol in the beers made from aged hops. The beers brewed with aged hops were described as more citrusy, while the beers brewed with fresh pellet hops were described as more "hop pellet-like", resinous, floral, and "green". The authors speculated that since these esters were not present in beers brewed without hops that they were derived from the humulone and lupulone oils in the hops during yeast fermentation <ref name="kishimoto_2007">[https://researchmap.jp/?action=cv_download_main&upload_id=110987 Odorants comprising hop aroma of beer: hop-derived odorants increased in the beer hopped with aged hops. Toru Kishimoto, Katsunori Kono and Kenkichi Aoki. 2007.]</ref>.
===Historic lambic hopping=Thiols==== [https://researchmap.jp/?action=cv_download_main&upload_id=110987 Kishimoto et al.] found an increase in the thiol 3-methyl-2-butene-1-thiol (MBT) in beers that were brewed with unidentified pellet hops (described in the study only as "a bitter variety of 11.5% alpha acid") that were aged for 30 days at 40°C versus using fresh pellet hops that were stored cold (4°C). Interestingly, this thiol was higher in beers where the aged hops were added to the boil rather than when they were added after the wort was cooled. The authors were not able to determine whether or not the MBT was derived from yeast fermentation, or from boiling the hops, but aging the hops increased the precursors for MBT <ref name="kishimoto_2007" />. MBT has been described as the thiol that produces the "skunky" aroma in lightstruck beer <ref>[http://www.aroxa.com/beer/beer-flavour-standard/3-methyl-2-butene-1-thiol/ 3-methyl-2-butene-1-thiol. Aroxa website. Retrieved 11/22/2016.]</ref>. ====See Also====* [https://www.morebeer.com/articles/storing_hops_properly "Hop Storage", MoreBeer blog. 07/15/2015.]* [https://www.balmyjuicebrewing.com/brewing-science/hop-freshness-1-hop-supply-chain/ Hop Freshness – Part 1: Hop Degradation and the Supply Chain] and [https://www.balmyjuicebrewing.com/brewing-science/hop-freshness-2-hop-bitter-acids Hop Freshness – Part 2: Hop Bitter Acids] by Balmy Juice Brewing.
===Aged Hop Suppliers===
* [https://www.yakimachief.com/commercial/hop-wire/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>[httphttps://www.hopsdirect.com/2013-products/choice-debittered-pellets/ Hops Direct "Choice Debittered/Aged Hops" (pelletPellet - 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 varietiesthat are aged for ~5 years and then pelletized <ref>Private correspondence with Dustin Carver by Farmhouse Brewing Supply. 03/22/2016.</ref>).]* [https://www.themaltmiller.co.uk/product/aged-hops/ The Malt Miller (UK).]* [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.* [https://www.ebay.com/itm/Lambic-Hops-pellet-or-whole-cone/172249202875?hash=item281ada40bb:m:mX2CSrKvWb0-3WIIuBh0aLA&var=471070249004 Ted from Hop Heaven on eBay sells 8 oz and 1 lb bags of aged pellet and leaf hops.] See this [https://www.facebook.com/groups/MilkTheFunk/permalink/4338527352842112/ MTF thread] on reviews of this product.* [https://shop.humle.se/humle/lambichumle/ Humlegårdens (Sweden); several varieties of aged whole leaf hops, 100 gram quantities.] ===Cryo Hops® and Debittered/"American Noble" Hops===[https://ychhops.com/hop-products/cryo-hops YCH Hops] has patented a process of extracting hop oils from hops using a proprietary cryogenic separation process that is claimed to preserve all of the components of each hop fraction. They also distribute the leftover hop material as [https://ychhops.com/connect/news/in-the-news/ych-hops-introduces-new-cryo-hops-product-line "Debittered Leaf" or "American Noble"]. These Debittered Leaf products have been reported to taste like low flavor/aroma/alpha versions of their original variety (for example, debittered Mosaic tastes like lower alpha Mosaic). They reportedly do not have the same character has aged "lambic" hops <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1748470578514482/?comment_id=1748488541846019&reply_comment_id=2162447193783483&comment_tracking=%7B%22tn%22%3A%22R%22%7D James Howat. Milk The Funk Facebook group thread about debittered leaf cryohops. 07/04/2018.]</ref>. ==Techniques=====Kettle and Mash Hopping===Kettle hopping sour beers can be a difficult thing for the new sour beer brewer. The usage of hops generally inhibits most lactic acid bacteria species, however there are many exceptions to this. Lactic acid bacteria can have a range of hop tolerance, with species such as ''Lactobacillus acetotolerans'' that tolerated Goose Island's Bourbon County Stout at 60 IBU <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1363048380390039/ MTF thread that reported an MBAA presentation by Brett Porter from Goose Island. 07/30/2016.]</ref>. Some breweries report that their house lactic acid bacteria can tolerate IBU ranges up to 10-20 IBU. White Labs claims that their ''L. delbuekii'' (WLP677) is tolerant of up to 20 IBU, however, most ''Lactobacillus'' cultures from yeast labs are not hop tolerant <ref>[http://www.themadfermentationist.com/p/commercial-cultures.html "Commercial Brettanomyces, Lactobacillus, and Pediococcus Descriptions; Commercial Yeast Laboratories." The Mad Fermentationist blog. Michael Tonsmeire. Retrieved 12/12/2016.]</ref>. See the [[Lactobacillus#Culture_Charts|''Lactobacillus'' culture charts]] and [[Lactobacillus#Hop_Tolerance|hop tolerance]] for more information. For both mixed fermentation sour beers and kettle sour beers, hops are often not used at all. In the case of kettle sours, sometimes brewers opt to add hops after the wort has been soured (see [[Wort Souring]]). Commercial brewers in the USA must by law use 7.5 pounds of hops for 100 barrels of beer <ref>[https://www.ttb.gov/rulings/2008-3.pdf "Classification of Brewed Products as “Beer” Under the Internal Revenue Code of 1986 and as “Malt Beverages” Under the Federal Alcohol Administration Act". TTB Ruling 2008, Number 2008-3. 07/07/2008. Retrieved 12/12/2016.]</ref> (malt beverages without hops can still be approved by the FDA instead of the TTB; contact the TTB for guidance <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1508230109205198/?match=ZGFuIHBpeGxleQ%3D%3D MTF thread with John Joyce and Joseph Kearns on TTB vs FDA approval for beer/malt beverages without hops. 12/13/2016.]</ref>). Since there is no US regulation for when the hops must be added, mash hopping might be a considered technique for commercial breweries in the US and in other parts of the world where hops are a requirement for beer (mash hopping retains only about 30% of the IBU that a 60 minute boiling addition does <ref>[https://www.homebrewersassociation.org/how-to-brew/resources/conference-seminars/ "Putting Some Numbers on First Wort and Mash Hop additions." David Curtis. 2014 National Homebrewers Conference presentation slides. Retrieved 12/12/2016.]</ref>). In historical German Berliner Weisse brewing, mash hopping or boiling hops during the decoction were also typical techniques (see [[Berliner_Weissbier#Historical|Berliner Weisse historical brewing]]). Another historical technique for adding hops to beer is to add a hop tea (hops boiled in water), for example in historical [http://www.garshol.priv.no/blog/331.html raw ale] brewing <ref>[http://www.garshol.priv.no/blog/331.html "Raw ale". Larsblog. Lars Marius Garshol. 05/06/2015. Retrieved 12/12/2016.]</ref>. For lactic acid cultures that are hop tolerant, hops can be used as a way to inhibit the amount of acid produced by them if the brewer desires this. Another advantage of using at least some hops in the kettle is that various compounds from hops contribute to head retention, and using a small amount of hops in the kettle (and perhaps dry hopping) can greatly assist with head retention in sour beers. A popular technique for [[100%25_Brettanomyces_Fermentation|100% Brettanomyces Fermentation]] is to use a typical IPA recipe. Hops do not inhibit ''Brettanomyces'' yeast. Some of the fruity characteristics of ''Brettanomyces'' can complement the fruity character of hops such as Citra, Amarillo, and Galaxy. For beers that are fermented with just ''S. cerevisiae'' and ''Brettanomyces'' but not lactic acid bacteria (such as some American farmhouse ales), Old World and noble hops are often used as well as North American and New Zealand/Australian citrusy hops, depending on what flavor and aroma profile the brewer is intending. See also:* [https://byo.com/stories/issue/item/3500-hoppy-sour-beers "Hoppy Sour Beers", Dec 2016 BYO article by Michael Tonsmeire.]* [https://www.facebook.com/groups/MilkTheFunk/permalink/3238859366142255/ MTF thread on barrel-aged NEIPA/dry hopping before barrel aging; inspired by Sour Hour Podcast #117 with Kevin Osbourne.]
==Glycosides and ''Brettanomyces''=Whirlpool Hopping===Hops contain glycosidesOn commercial systems, which are flavor compounds that are bound to adding hops during the whirlpool has become a sugar moleculecommon technique. In their bound formThe idea is that hopping during the whirlpool will decrease the amount of isomerization of alpha acids in the final beer, glycosides are flavorless. Enzymatic activity from some strains of ''Brettanomyces'' can release these bound compounds and release their while providing flavor and aromatic potentialaroma from the hops. See the [[Brettanomyces#Glycosides_and_Beta-Glucosidase_Activity|''Brettanomyces'']] page for details.
Aaron Justice reported that a considerable amount of isomerization occurs on both a 150 BBL system (75-90 minutes of total steeping time), a 50 BBL system (65-80 minutes of total steeping time), and a 5 BBL pilot system (35-40 minutes of total steeping time). Justice reported an average of 30% utilization (the amount of iso-alpha acids from the potential alpha acids), with a 12.2% deviation. The deviations were based on the gravity of the wort and the amount of hops added before the whirlpool. With lower gravity worts and worts with less kettle additions, a high increase in utilization was observed. Most of the IBU's were gained within the first 10 minutes of the whirlpool, with only very small increases in IBU (~3 IBU) after 10. This data indicates that the total whirlpool steeping time and thus brewhouse size does not necessarily have a large impact in the amount of isomerization that occurs during commercial whirlpooling. The temperature of the whirlpool was not reported <ref name==Antimicrobial Properties=="justice_2018" />.
===Dry Hopping===
[https://beerandbrewing.com/dictionary/96jvGQTSdT/ Dry hopping] is the technique of adding hops to beer that has finished fermenting or is in the process of fermenting. Historically, dry hopping is associated with English pale ales of the 1800's, and it was re-discovered by Fritz Maytag of Anchor Brewing Company in 1975 when the company brewed the first American IPA, Liberty Ale <ref>[https://beerandbrewing.com/dictionary/96jvGQTSdT/ "The Oxford Companion to Beer definition of dry hopping," Garrett Oliver. Craft beer & Brewing Magazine. Retrieved 11/16/2023.]</ref><ref>[https://northamericanbrewers.org/liberty-ale/ "Liberty Ale". North American Brewers Association. April 28, 2022. Retrieved 11/16/2023.]</ref><ref>[https://www.youtube.com/watch?v=4ijHO5TFG3I Scott Ungermann, Brewmaster of Anchor Brewing Company. The Doug Piper Gourmet Brewing Podcast. July 14th, 2023.]</ref>(20 mins in). Brewers have had positive and interesting results dry-hopping sour and funky beer. Often fresh American or New Zealand varieties that complement fruit flavors are chosen, however, other varieties have been used as well, including English and German hops. Just as in dry hopping normal beers, dry hopping sour/funky should be done after the beer has matured. Dry hopping for around 1-3 days before [[packaging]] the beer is adequate for extraction, depending on whether or not the beer is recirculated or agitated (agitation of the beer while on contact with the dry hops attains full extraction in 24 hours) <ref>[http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/34093/Wolfe_thesis.pdf?sequence=1 A Study of Factors Affecting the Extraction of Flavor When Dry Hopping Beer (master thesis). Peter Harold Wolfe. 2012.]</ref>. Hopping rates generally range from 0.5-1 ounces per 1 gallon of beer (1-2 pounds per bbl or 3.7-7.5 grams per liter) to achieve hop-forward flavors, although lesser rates can be used to achieve a more subtle character (see the threads below) <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1693639013997639/?comment_id=1693660390662168&comment_tracking=%7B%22tn%22%3A%22R4%22%7D Nate Walter and Dan Pixley. Milk The Funk Facebook group. 05/21/2017.]</ref>. Dry hopping can contribute to bitterness in beer through oxidized alpha acids and oxidized beta acids. Oxidized alpha acids can also reduce iso-alpha acids in beers that begin with more than 25 IBU from iso-alpha acids, potentially reducing percieved bitterness after dry hopping (see [[Hops#Acids_2|Oxidized Alpha Acids]] above). Some alpha acids will also dissolve into the beer, which are estimated as being 10% as bitter as iso-alpha acids. Dry hopping also has a linear impact on the pH of beer regardless of the starting IBU or pH: the pH rises by 0.14 per pound of hop pellets per barrel of beer in a beer that started with a pH of 4.2 (~0.5 ounces per gallon or 3.7 grams per liter) <ref name="Maye_2016" /><ref name="Shellhammer, Vollmer and Sharp, CBC 2015"/>. This rise in pH might be less in more acidic beers that are dry hopped since pH is a logarithmic scale. Dry hopping can also reduce head retention in beers, although this is variety dependent (one study found that dry hopping with Eureka and Apollo hops increased head retention, while dry hopping with Bravo, Centennial, and Cascade decreased head retention). Extended dry hopping times (after 3 days) can also reduce head retention <ref name="Maye_EBC2017" />. See also:* [http://thebrulab.libsyn.com/episode-079-impact-dry-hopping-has-on-bitterness-ibu-and-ph-w-dr-john-paul-maye Bru Lab podcast Episode 079 - Impact Dry Hopping Has On Bitterness, IBU, and pH w/ Dr. John Paul Maye.]* [https://www.therarebarrel.com/index.cfm?method=blog.blogDrilldown&blogEntryID=8141D6FA-EE78-5BCE-E08E-704DB6EEA279&originalMarketingURL=blog/Dry-hopped--Changing-process-leads-to-bottling The Rare Barrel reports on an anecdote that dry hopping in a less sour beer extracts better hop aroma, and ''Brettanomyces'' preserves the character.]* [https://www.facebook.com/groups/MilkTheFunk/permalink/2358742877487246/ MTF thread by Dave Janssen on experiences with doing long-term dry hopping with noble hops in sour beers.] See also [http://www.horscategoriebrewing.com/2018/11/saison-from-1911-finishing-hops-and.html Dave's research on a 1911 saison that was dry hopped long term].* [https://www.facebook.com/groups/MilkTheFunk/permalink/2718954364799427/ MTF thread on the possibility/mechanism of dry hopping contributing to the "funky" character of sour beers.]* [https://www.facebook.com/groups/MilkTheFunk/permalink/2828125150549014/ MTF thread on dry hopping with aged hops.]* [https://www.facebook.com/groups/MilkTheFunk/permalink/12846186548996792994066257288235/ MTF thread from Benedikt Koch on using very aged hops in a natural cider, inspired by Revel Cider.] ====Inhibiting Lactic Acid Bacteria====Dry hopping inhibits Gram-positive bacteria such as ''Lactobacillus''. Humulinic acids have been found to greatly inhibit bacteria (see [[Hops#Antimicrobial_Properties|Antimicrobial Properties]]). Other compounds such as non-isomerized alpha acids, oxidized hop acids, or the small amount of isomerization of alpha acids that happens in beer at room temperature <ref>[http://scottjanish.com/zero-hot-side-hopped-neipa-hplc-testing-sensory-bitterness/ Janish, Scott. "Zero Hot-Side Hopped NEIPA | HPLC Testing for Sensory Bitterness". ScottJanish.com. Retrieved 03/09/2017.]</ref>, could contribute to inhibiting lactic acid bacteria. See [[Hops#Antimicrobial_Properties|antimicrobial properties]] above. See also reported data below. * [https://www.facebook.com/groups/MilkTheFunk/permalink/1416506428377567/?comment_id=1458425540852322&comment_tracking=%7B%22tn%22%3A%22R%22%7D Caroline Whalen Taggart's data point on the effects of dry hopping on ''L. plantarum'' (GoodBelly). No hops finalized at a pH of 3.53, and the dry hopped version finalized at a pH of 4.35.] She used around 4 grams per gallon of 10-15 AA hops <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1746176672077206/?comment_id=1746211618740378&comment_tracking=%7B%22tn%22%3A%22R0%22%7D Carloine Whalen Taggart. Milk The Funk Facebook group. 07/06/2017.]</ref>.* Per Buer's experiment on the effects of dry hopping on ''Lactobacillus'':: <youtube width="300" height="200">J2g5P7ZlGn4</youtube>* [https://www.ratebeer.com/forums/lab-and-hops_289071.htm "CLevar" on Ratebeer.com data point on ''Lactobacillus'' being inhibited by hops, but not as much by iso-alpha acid hop extract.] ====The Freshening Power of the Hop (Hop Creep)====Also known as "dry hop creep", it was first discovered in 1893 by Brown and Morris that dry hopping increases the ABV of beers and dries them out. Dry hop creep, along with the secondary fermentation of ''Brettanomyces'' in long aged British ales of the late 19th and early 20th centuries, were once characterized as the potential mechanisms by which long aged ales could retain a high level of carbonation in casks <ref>[https://archive.org/details/principlespracti00syke "The principles and practice of brewing" Sykes, Walter John. London, C. Griffin and Company, limited, 1907. Pgs 384-388.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/4709953772366133 Gareth Young. Milk The Funk Facebook group thread about English brewers historically relying on Brettanomyces and dry hop creep for carbonation in long aged ales. 06/17/2021.]</ref>. It was proposed that the likely cause is the release of glycolytic enzymes that break down starches into sugars which viable yeast can then ferment. Brewers normally aim to control the final alcohol percentage in a beer through brewhouse operations rather than postfermentation dilutions with lower/higher alcohol beers or water. This approach to brewing is called "brewing to final gravity." Due to the need to have a predictable ABV for government regulatory reasons, unexpected fermentation is, therefore, a concern for many breweries <ref name="Kirkendall_2018">[https://www.tandfonline.com/doi/abs/10.1080/03610470.2018.1469081?journalCode=ujbc20 The Freshening Power of Centennial Hops. Jacob A. Kirkendall, Carter A. Mitchell & Lucas R. Chadwick. 2018. DOI: https://doi.org/10.1080/03610470.2018.1469081.]</ref>. Hop creep can also result in additional attenuation and higher carbonation after packaging, as well as diacetyl production. Historically, there have been two studies published on the phenomenon of hops releasing glycolytic enzymes that break down starches during dry hopping: [http://barclayperkins.blogspot.com/2018/03/why-dry-hop.html Brown and Morris (1893)] and [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1941.tb06070.x Janicki et al. (1941)]. More recently, several researchers and brewers have revisited this phenomenon. Brown and Morris (1893) discovered that hops could break down maltodextrin, but failed to identify the enzymes from the hop plant material and hypothesized (probably incorrectly) that tannins were inhibiting the enzymes. Janicki et al. (1941) came to similar conclusions regarding the enzymes and tannin inhibitors, and they also concluded that the enzyme activity was independent of hop variety, geography, age, storage conditions, pH values between 4.1 and 4.8, and that one or more additional unknown factors were at play <ref name="Kirkendall_2018" />. More recent studies have shown that there is a difference in this enzymatic power between different hop varieties. [https://www.asbcnet.org/publications/journal/vol/2017/Pages/ASBCJ-2017-2257-01.aspx Cibaka et al. (2017)] reported an increase in ABV when dry hopping with Amarillo and Sorachi Ace hops, but not when dry hopping with Citra or Hallertau Blanc. Interestingly, they also found that Mosaic hops resulted in the opposite effect; the Mosaic dry hopped beer dropped from 4% ABV to 3.6% ABV. It was hypothesized (possibly incorrectly) that Mosaic hops might release some sort of unidentified molecule that inhibits yeast fermentation/growth or viability. Cibaka et al. (2017) also demonstrated that late kettle additions might work to combat dry hop creep; the beer dry hopped with 2 g/L of Sorachi Ace finished at 5.1% ABV, while a beer that received a late kettle addition of 2 g/L of Sorachi Ace in addition to 2 g/L of Sorachi Ace dry hop finished at 4.3% ABV (the control with no dry hop finished at 4.0% ABV) <ref name="Kirkendall_2018" />. Kirkendall et al. (2018) found that hop varieties also have a varying ability to ferment dextrins. They reported the following ABV increases when dry hopped in a pale ale at one pound per barrel: Centennial hops (+0.27%), Citra (+0.12%), Simcoe (+0.33%), Cascade (+0.49%) and Amarillo (+0.49%). Prolonged contact with Centennial hops (42 days) increased the ABV even more so and resulted in a nearly 1% ABV increase. Rousing the hops into suspension hastened the increase in ABV compared to samples that were left still. From their results, it appears as though contact with hops during dry hopping continues the breakdown of starches and dextrins into fermentable sugars. They also concluded that dry hopping at a temperature that is too cold for the yeast strain in the beer to ferment resulted in no change in ABV. They compared the enzymatic activity of Centennial hops that were stored at -20°C versus room temperature storage and found that there was no significant difference, indicating that the unidentified enzymes are relatively stable <ref name="Kirkendall_2018" />. Kirkpatrick and Shellhammer (2018) found that the enzymes responsible for the conversion of dextrins into sugars include amyloglucosidase (removes glucose from non-reducing ends of α-1,4 and branching α-1,6 linkages, with a preference for α-1,4 linkages and longer chain oligosaccharides), α-amylase (hydrolyzes randomly along glucopolysaccharides to produce maltose, maltotriose, maltopentaose, and maltohexaose products from amylose as well as maltose, glucose, and branched dextrins from amylopectin), β-amylase (saccharifiying enzyme, cleaving maltose in small amounts from nonreducing ends of glucopolysaccharides, and to a minor extent, maltotriose), and limit dextrinase (debranches limit dextrins at α-1,6 linkages, producing linear α-1,4 chains which can further be degraded by the combined action of amylases). They were able to successfully extract them from Cascade pellet hops using commercially available assays (enzyme specific para-nitrophenyl blocked oligosaccharide substrates). The amount of α and β-amylase found in Cascade hops was well below that of malted barley, but within the range reported in other plant leaves. These enzymes are denatured by high temperatures, and as such would be denatured when boiling hops. They reported a similar increase in ABV of 1.3% after 40 days when dry hopping a beer with Cascade hops (and a decrease of 1.9°P) at a rate of 10 g/L. They also found that the hops contained glucose and a small amount of fructose, which accounted for a sugar increase of 0.02−0.03 °P per gram of hops. More studies on whether or not the amount of dry hopping has a large effect needs to be done, and whether or not warmer temperatures speed up the enzymatic breakdown of dextrins, and the authors hypothesized that the rate of dextrin break down could be slowed by dry hopping at lower temperatures <ref name="Kirkpatrick_2018">[https://pubs.acs.org/doi/pdf/10.1021/acs.jafc.8b03563 Evidence of Dextrin Hydrolyzing Enzymes in Cascade Hops (Humulus lupulus). Kaylyn R. Kirkpatrick and Thomas H. Shellhammer. 2018. DOI: DOI: 10.1021/acs.jafc.8b03563.]</ref>. Rubottom and Shellhamer (2023) later demonstrated that drying hops at 150°F reduced the amount of enzymes in dried pellitized hops versus drying them at 130°F <ref>[https://www.tandfonline.com/doi/abs/10.1080/03610470.2023.2194838 Evaluating the Impact of High and Low Kilning Temperatures on Popular American Aroma Hops. Lindsey N. Rubottom, Thomas H. Shellhammer. Received 07 Feb 2023, Accepted 21 Mar 2023, Published online: 28 Apr 2023. https://doi.org/10.1080/03610470.2023.2194838.]</ref>. Kirkpatrick and Shellhammer (2018) also reported that the exposure time of the beer to the dry hop material played a significant role in the breakdown of dextrins. Most of the breakdown of dextrins occurs within 5 days (+0.7% ABV), but continued slowly up until at least 40 days (+1.3%). They also tested removing the hops via centrifuge and storing the beer at 10°C or 20°C. Their results suggested that the effect of the enzymatic breakdown of dextrins by hops appears to only be active when in contact with the hops and that once the beer is removed then this breakdown of dextrins stops. The authors suggest that to avoid as much breakdown of starches and over-attenuation from dry hops as possible, brewers can limit the amount of time sits on the hops and reduce the temperature, however, it is also important to consider how this might impact the product's flavor and careful measures should be taken to balance the over-attenuation problem and overall beer quality <ref name="Kirkpatrick_2018" />. After removing the beer from the hops, a second diacetyl rest has been suggested as a way to clean up any diacetyl or off-flavors that the yeast produces from the additional fermentation during dry hopping <ref>[https://www.rockstarbrewer.com/how-dry-hop-creep-causes-diacetyl-in-beer-and-how-brewers-can-minimise-the-risk/ STEVE 'HENDO' HENDERSON. How “Dry Hop Creep” Causes Diacetyl In Beer and How Brewers Can Minimise The Risk. Rockstar Brewer Academy website. 09/03/2018. Retrieved 10/05/2018.]</ref>. Other recommended solutions to avoiding hop creep is pasteurizing, filtering, or cold crashing out the yeast before dry hopping, storing the beer cold so that the yeast remains inactive, reducing dry hopping amounts, and dry hopping before fermentation is finished <ref>[http://beersmith.com/blog/2019/03/31/dry-hop-creep-over-carbonation-and-diacetyl-in-beer/ Brad Smith. BeerSmith blog. 03/13/2019. Retrieved 07/23/2019.]</ref>. [https://www.mbaa.com/publications/tq/tqPastIssues/2021/Pages/TQ-58-3-0705-01.aspx Teraoka et al. (2021)] argued that enzymes present in dry hops are not derived from the hop plants themselves, but microbes living on the hops and that the reported variability of starch degrading enzymes present in hops is due to the varying environmental conditions created by drying hops that encourage or discourage microbial growth. It has been reported that proteobacteria are the dominant type of bacteria that grow on hops, with the majority of them being Pseudomonas and Sphingomonas, with Pseudomonas having being previously reported to produce alpha-amylase. However, the authors recommend that further research is needed to identify which microbe species might be producing these enzymes on hops. They found that hops treated with the anti-microbial chemical sodium azide resulted in hops with much lower starch degrading enzymes. They also reported that alpha-amylase decreased in dried leaf and pellet hops over 3 months of anaerobic storage (storage temperature did play a role in the degradation rate of the enzymes). Alpha-amylase stayed relative consistent in fresh hops during storage. Beta-amylase remained stable over the three month storage time regardless of hop type. The authors also acknowledge another possible variable being that hop seed material might contain starch; however, seeded hops are generally not used in the brewing industry <ref>[https://www.mbaa.com/publications/tq/tqPastIssues/2021/Pages/TQ-58-3-0705-01.aspx "Do Starch-Degrading Enzymes in Hop Samples Originate in Microorganisms?" Ryohei Teraoka (1), Makoto Kanauchi (1), and Charles W. Bamforth (2). 1. Department of Food Management, Miyagi University, Hatatate Taihaku-ku Sendai Miyagi, 982-0215, Japan. 2. Sierra Nevada Brewing Company, Chico, CA 95928, U.S.A.]</ref>. See also [https://www.masterbrewerspodcast.com/229 MBAA Podcast episode 229 "Is Hop Creep Caused by Microorganisms?" with Dr. Charlie Bamforth]. [https://www.mdpi.com/2311-5637/7/2/66/html Bruner et al (2021)] investigated whether or not yeast strain selection has an impact on hop creep with the goal of finding if any strains would reduce the potential for dry-hop creep. They examined 30 different ''Saccharomyces'' yeasts from different yeast labs, and measured the [https://beerandbrewing.com/dictionary/gaKDNn0yxE/ real degrees of fermentation (RDF)] that occurred after dry-hopping post fermentation. With the exception of two strains, all of the yeasts re-fermented the beer after dry hopping, indicating that yeast strain selection won't reduce the chances for dry hop creep. There were two exceptions to this. The first was a diastatic strain of ''Saccharomyces cerevisiae'' (SafAle™ BE-134), which was able to break down starches in the beer prior to dry hopping due to the [[Saccharomyces#Diastatic_strains_of_Saccharomyces_cerevisiae|diastatic properties]] of this yeast strain. The other exception was a strain of ''Saccharomyces mikatae'' that is used as a co-fermenter in wine fermentations and is a poor attenuater of wort. The study also found no correlation between flocculation and attenuation from dry-hop creep, but suggested that further research be done to investigate the belief that higher flocculating strains could reduce the negative effects of subtle dry hop creep <ref>[https://www.mdpi.com/2311-5637/7/2/66/html Bruner J, Marcus A, Fox G. Dry-Hop Creep Potential of Various Saccharomyces Yeast Species and Strains. Fermentation. 2021; 7(2):66. https://doi.org/10.3390/fermentation7020066.]</ref>. See also:* [https://www.asbcnet.org/events/archives/2017ASBCMeeting/proceedings/2017Proceedings/35_Kirkpatrick.pdf Kirkpatrick and Shellhammer poster at the 2017 ASBC Annual Meeting.]* [http://www.qclscientific.com/pdfs/BeerLab/009CS-FD%20Northern%20Monk.pdf CDR BeerLab® experiment showing dry hop creep effects.]* [https://www.rockstarbrewer.com/how-dry-hop-creep-causes-diacetyl-in-beer-and-how-brewers-can-minimise-the-risk/ Article on Rockstar Brewer Academy on how dry hop creep can cause diacetyl.]* [http://brewcon.org.au/dry-hop-creep-dry-hopping/ Dry Hop Creep presentation by Caolan Vaughan in Australia.]* [https://www.craftbrewersconference.com/wp-content/uploads/2017_presentations/Tom-Shellhammer_02.pdf CBC presentation on dry hop creep by Allagash Brewing Company.]* [https://www.thebrewingnetwork.com/hop-and-brew-school-ep8-hop-creep/ Methods for avoiding hop creep and diacetyl production from hop creep explained by Nick Zeigler ("Hop and Brew School" podcast).]* [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]. See also:* [http://www.horscategoriebrewing.com/2017/03/lambic-characteristics-fg-and-ibus-in.html "Lambic characteristics - FG and IBUs in Geuze" on Hors Categorie blog.]* [http://www.horscategoriebrewing.com/2016/04/hops-in-spontaneous-fermentation.html "Hops in spontaneous fermentation" on Hors Categorie blog.]* [https://www.facebook.com/groups/MilkTheFunk/permalink/2811991652162364/ MTF discussion on methods of aging leaf and pellet hops.]* [https://www.facebook.com/groups/MilkTheFunk/permalink/1760069707354569/ MTF discussion on the general benefits of using aged hops in sour beers.]* [https://www.facebook.com/groups/MilkTheFunk/permalink/2503097546385111/ MTF discussion on IBU's, alpha acids, oxidized bittering compounds, etc. might play a role in aged pellet hops.]* [[Lambic]]* [[Spontaneous Fermentation]]* [[Gueuze and Lambic Character]] ===Historic hopping in lambic and other mixed-fermentation beer=== While modern lambic uses aged hops almost exclusively, it was common for historic lambic to blend both aged and fresh hops<ref name="Hors Catégorie Brewing Hops in Spontaneous Fermentation"> [http://www.horscategoriebrewing.com/2016/04/hops-in-spontaneous-fermentation.html Dave Janssen's discussion of hopping in spontaneous fermentation] </ref>. The exact ratio of fresh to aged hops changed over time and could vary depending on the harvest (poor hop years may have relied more heavily on aged hops while years of good harvests would make more use hops of the recent harvest). In addition to the difference in hop age between modern and historic lambic, hopping rates also differ significantly between modern and aged hops. It is important to note that the quality of these hops are certainly different from modern hops, and that hop origin could have a significant influence on suggested hopping rates <ref name="Hors Catégorie Brewing Hopping Grisette"> [http://www.horscategoriebrewing.com/2016/06/hopping-historical-grisettes.html Dave Janssen's discussion of hopping grisettes] </ref> (see the hopping rate table and notes regarding hop origin conversion factors from historical texts). While hop quality would have improved moving to the modern day while hopping rates were dropping, there is mention in historic lambic literature of lambic in the late 1800s being more bitter than lambic from the mid-1900s (and, subsequently, similar to historic saison in the increased hop presence in a mixed-fermentation beer)<ref name="Hors Catégorie Brewing Hops in Spontaneous Fermentation"/> Historical documents dealing with Belgian brewing show a steady progression from high doses of fresh hops in lambic to the sort of hop composition and origin that are in use today. In 1851 Lacambre mentions rates for Belgian hops of 760-860 g/Hl and specifically highlights the use of young hops. Belgian brewing scientist Henri Van Laer recommended a hopping rate of 700-800 g/Hl in 1890, roughly in agreement with Lacambre though slightly lower. In the early 1900s, citing information from 1896, ''Le Petit Journal du Brasseur'' mentions a hopping rate of 540 g/Hl using a mix of Belgian and Bavarian hops and a split of 2/3 young, 1/3 old in good years (and 50/50 in bad years). In 1928 ''Le Petit Journal du Brasseur'' recommends a larger proportion of aged hops (2/3 aged, 1/3 fresh) and rates of 600g/Hl of Belgian hops<ref name="Hors Catégorie Brewing Hops in Spontaneous Fermentation"/>. Considering the difference in strength in German and Belgian hops<ref name="Hors Catégorie Brewing Hopping Grisette"/>, this fits with a stable or decreasing hopping rate from that given in the early 1900s. In 1937 exclusive use of aged hops is recommended, though as noted in 1946, year old hops may be preferable to hops that were aged longer in poor conditions<ref name="Hors Catégorie Brewing Hops in Spontaneous Fermentation"/>. Also in the 1940s ''Le Petit Journal du Brasseur'' recommends hopping rates of 400-500 g/Hl, roughly in agreement with modern times, and notes that the lambic of this time was softer than historic lambic<ref name="Hors Catégorie Brewing Hops in Spontaneous Fermentation"/>. (In Progress)Lambics aren't the only historic mixed-fermentation beer to make use of aged hops. Though the specific mention of aged hops for saison and bieres de garde does not seem to be the norm, aged hops were used at times, such as when more acidity was desired. These hops were also more likely to be used toward the beginning of the brewing season in months like October where the current harvest may have been considered too fresh for proper use. Notes: Give some discussion of hopping saison and bieres de garde. See [http://www.horscategoriebrewing.com/2016/06/hopping-historical-grisettes.html hopping grisette table] for some hopping rates, PJB, etc. James Howat of Black Project Spontaneous Ales uses 0.5 ounces of aged hops per gallon of beer for spontaneously fermented beers brewed using traditional lambic techniques <ref>[https://www.facebook.com/blackprojectbeer/videos/580667305468055/ Howat, James. Facebook live video stream. 12/23/2016. ~5:30 minutes in.]</ref>. See also:* [https://www.facebook.com/groups/MilkTheFunk/permalink/1923361737692031/ MTF discussion on using aged hops in other styles of beers, including historical references and tips on producing lambic-like character from aged hops and commercial cultures.]* [https://www.facebook.com/groups/MilkTheFunk/permalink/2534320159929516/ MTF discussion on leaving hops beer fermented with ''Brettanomyces'' long term; inspired by historical English brewing methods.] ===Spent Hops===There has been some research and experimentation on using spent hops (mostly spent dry hops) in a second beer.* [https://www.facebook.com/groups/MilkTheFunk/permalink/3280694625292062/ MTF thread containing summaries of science and historical use of re-using spent hops.] ===Hop Extract Products===* [https://www.stitcher.com/show/craft-beer-brewing-magazine-podcast/episode/episode-202-brandon-capps-of-new-image-brews-better-ipas-through-chemistry-86471398 Craft Beer & Brewing Magazine Podcast Episode 202: Brandon Capps of New Image Brews Better IPAs Through Chemistry.]
==See Also==
===Additional Articles on MTF Wiki===
* [[Cantillon]]
* [[Glycosides]]
* [[Spontaneous Fermentation]]
* [[Lactobacillus]]
* [[Lambic]]
===External Resources===
* [https://www.tandfonline.com/doi/suppl/10.1080/03610470.2023.2232267/suppl_file/ujbc_a_2232267_sm7384.pdf "Free Exhaustive Literature Review on Hops (Humulus lupulus L.)," Keven Bélanger Harbour; Journal of the American Society of Brewing Chemists.]
* [https://www.barthhaas.com/resources/hop-harvest-guide#!download BarthHaas Hop Harvest Guide with flavor wheels.]
* [https://appellationbeer.com/blog/hop-queries/ "Hop Queries"; Stan Hieronymus's hops newsletter.]
* [https://www.youtube.com/channel/UCYi3RcKUPk9hCOxaN4TCoHQ/videos Hop Growers of America video presentations (YouTube).]
* [https://ext.vt.edu/agriculture/commercial-horticulture/hops.html Virginia Tech Virginia Cooperative Extension "Hops" webpage: growing and agriculture resources.]
* [https://lisameoli.wordpress.com/2015/11/04/the-hop-plant-dissected/ "The Hop Plant Dissected" by Lisa Meoli, 2015.]
* [https://byo.com/stories/issue/item/3500-hoppy-sour-beers "Hoppy Sour Beers", Dec 2016 BYO article by Michael Tonsmeire.]
* [http://scottjanish.com/dry-hopping-effect-bitterness-ibu-testing/ "Dry Hopping Effect on Bitterness and IBU Testing" by Scott Janish.]
* [https://ychhops.com/varieties YCH hop variety database.]
* [https://www.youtube.com/watch?v=J2g5P7ZlGn4 Per Buer's Video Demonstration of how dry hopping inhibits ''Lactobacillus''.]
* [http://www.centralstatebrewing.com/blog/2015/7/1/whats-that-smell-eraroma-compound Blog Article on Brett and Glycosides by Cy Wood.]
* [http://www.garshol.priv.no/blog/337.html "How hops prevent infection", by Lars Garshol.]* [http://www.homebrewtalk.com/unlocking-hop-and-fruit-flavors-from-glycosides.html "Unlocking Hop and Fruit Flavors from Glycosides", HBT article by Dennis L Waldron.]
* [http://beerlegends.com/hops-varieties Beer Legends Hop Varieties - gives vital statistics on hops including acid content, physical cone characteristics, storage and growth details, and oil content.]
* [http://l.facebook.com/l.php?u=http%3A%2F%2Fwww.ttb.gov%2Frulings%2F2008-3.pdf&h=lAQEJ1NPf TTB Hop Requirements for USA commercial breweries.]
* [http://www.horscategoriebrewing.com/2016/04/hops-in-spontaneous-fermentation.html Blog article on hops in spontaneous fermentation by Dave Janssen]
* [http://www.lugwrenchbrewing.com/2011/11/cohumulone-rages-by-hop-variety-hop.html Cohumulone ranges by hop variety.]
* [https://phdinbeer.com/2018/05/04/crispr-yeast-and-hop-compounds/ "CRISPR Yeast and Hop Compounds" by Dr. Matt Humbard; a critical response of yeast being modified to make two hop compounds.]
* [https://patspints.com/2019/01/16/the-surprising-science-of-dry-hopping-lessons-from-tom-shellhammer/?fbclid=IwAR1QOAFBjzXLGeSftpgYuuwaWkjqiEZL41_cLogTWwWmoCbpzowRgAYCmJ4 Summary of a Shellhammer presentation on dry hop saturation, bitterness from dry hopping, and hop creep (Pat's Pints blog, Jan 2019).]
* [http://www.thebrewingnetwork.com/hop-and-brew-school-ep11-hops-and-sour-beer/ Hop and Brew School podcast interview with Vinnie Cilurzo from Russian River Brewing, Jay Goodwin from The Rare Barrel and Charlie Johnson from the Ronin Fermentation Project on using fresh and aged hops in sour beer.]
* [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==