Changes

'''Alpha acids''' (also called "humulones" and abbreviated as "α-acids") in hops mostly consist of humulone, cohumulone, and adhumulone. The ratio of these individual acids to each other can vary based on hop variety much like total iso-α-acid percent, though generally the primary acids are humulone and cohumulone. Cohumulone has been identified by some researchers as a source of a more harsh bitterness, although similar research contradicts this statement <ref>[http://www.scielo.br/scielo.php?pid=S0100-40422000000100019&script=sci_arttext&tlng=es Fundamentals of beer and hop chemistry. Denis De Keukeleire. 1999.]</ref>. While alpha acids are mostly insoluble in wort at typical brewing pH (alpha acids become much more soluble as the pH rises towards 5.9 to 7, which is not typical for wort production <ref name="Bastgen_2019">[https://www.tandfonline.com/doi/full/10.1080/03610470.2019.1587734 Influencing Factors on Hop Isomerization Beyond the Conventional Range. Nele Bastgen, Tobias Becher & Jean Titze. 2019. DOI: https://doi.org/10.1080/03610470.2019.1587734.]</ref>), the isomerized alpha acids (also called isohumulones) which are formed during boiling are soluble. Isomerization leads to roughly a 70%/30% split between ''cis'' and ''trans'' iso-α-acids respectively, with ''cis'' iso-α-acids being more stable over time and more bitter<ref name="Schönberger and Kostelecky, 2012"> [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2011.tb00471.x/abstract Schönberger and Kostelecky, 2012]</ref>. Alpha acids themselves do not taste bitter, but isomerized alpha acids (iso-α-acids/isohumulones) contribute to the bitterness of beer and have antimicrobial properties. Isocohumulone is often cited as being more harshly bitter than the other iso-α-acids, but studies of taste perception of individual iso-α-acids have not agreed with this. However isocohumolone , iso-cohumolone is slightly more soluble than the other acids and therefore a hop with a higher cohumulone composition may result in a beer with higher iso-α-acid for hops of equal iso-α-acid percent and use in brewing but different iso-α-acid breakdown<ref name="Schönberger and Kostelecky, 2012"/>. Alpha acids are susceptible to oxidation and the alpha acid content of a hop will decrease with storage. There is evidence to show that during wort boiling iso-humulone and perhaps also iso-cohumulone bind with the head forming proteins, Lipid Transfer Protein (LTP) and Protein Z, to help form foam-positive structures in beer. These iso-alpha acids bind less so with LTP than they do with Protein Z. The resulting bound structures have been described as "vesicles", which are protein "bubbles" with thick surface layers <ref>[https://www.sciencedirect.com/science/article/pii/S0268005X19325391 Vesicular structures formed from barley wort proteins and iso-humulone. Yi Lu, Peter Osmark, Björn Bergenståhl, Lars Nilsson. 2020.]</ref>.