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'''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, meaning . Maye et al. (2016) showed that humulinone formation occurs 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). Scientists believe 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" />.