13,600
edits
Changes
Hops
,no edit summary
==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; however (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 and can be used for microbial inhibition. In addition to their antimicrobial activity aged hops contribute important flavor and aroma compounds and precursors to beer.
In [[lambic]] brewing, the term '''aged hops''' refers to these hops which have been aged for 2+ years in non-refrigerated conditions, and in burlap sacks or some other oxygen permeable bag <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|Aged Hops in Lambic]].
Oxidized alpha acids (humulinones) are similar in taste perception to iso-α-acids, but have been described as less bitter (about 66% as bitter) <ref name="Shellhammer, Vollmer and Sharp, CBC 2015"/><ref name="Maye_2016" />. 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 20 IBU's, but not in beer with less than 25 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]). In beers with less than 25 IBU, high dry hopping rates greatly increase the bitterness/IBU due to the bitter humulinones. The rate of humulinone formation is limiting, meaning that humulinone formation occurs rapidly during hop pelletization, and the concentration peaks during this time (researchers found that further exposure to air did not increase humulinone content). Scientists believe 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 lupuline glands are broken. The exact mechanism by which alpha acids are converted to humulinones is not known <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 perception of bitterness, specifically hulupones. Unlike humulinones which form relatively quickly from oxidation of alpha acids, hulupones form at a much slower rate <ref name="Dušek_2014" />. While some sensory analysis of beers containing oxidized beta acids describe 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" />. Weight for weight, hulupones are 35-40% as bitter as iso-alpha acids <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>. Two other compounds other than hulupones have been identified as being caused produced by oxidized the oxidation of beta acids, epoxycohulupone and epoxyhulupone, however their . Their effect on beer flavor is not yet known , however it is thought that hulupones have the greatest impact on beer flavor <ref name="Dušek_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 <ref name="Algazzali_2014" />.
[[File:Lam Hop Oils.jpg|thumb|upright=2.5|[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.]]