Changes

(in progress) The main compounds of interest to brewers in hops are their bitter acids and oils. Alpha acids account for roughly 2-Makeup 12% of dried hops: quick overview by mass, beta acids account for roughly --- % and oils account for roughly ----, though the exact percentages will vary depending on factors such as the hop varietal, growing region, harvest time, and growth conditions for the year. The primary '''alpha acids''' in hops are humulone, cohumulone, and adhumulone. The ratio of these individual acids to each other can vary much like total iso-α-acid percent, though generally the primary acids are -------. While alpha acidsare insoluble in wort, the isomerized acids which are formed during boiling are soluble. Isomerized alpha acids (iso-α-acids) 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, beta but studies of taste perception of individual iso-α-acids, oils, have not agreed with this (---source---). However Isocohumolone is slightly more soluble than the other compoundsacids 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. Iso-α-acids are susceptible to oxidation and the iso-α-acid content of a hop will decrease with storage. '''Beta Acids''' are similar in structure to iso-α-acids but they are not able to isomerize and are therefore not soluble in wort. '''Oils'''

Another antimicrobial mechanism resulting from oxidative stress has been attributed to both iso-α-acids and humulinic acids<ref name="Schurr et al, 2015"> [http://www.sciencedirect.com/science/article/pii/S0740002014002470 Schurr et al., (2015)] </ref>. Humulinic acids are either not bitter tasting or much less bitter than iso-α-acids but are similar in structure to and are formed from the degradation of iso-α-acids. This oxidative stress-driven antimicrobial activity is due to potential for oxidation-reduction (redox) reactions within bacterial cells between Mn2+ ions and these specific hop acids within the cell, which . The redox potential is due to different conditions inside (higher pH, higher Mn2+) and outside (lower pH, lower Mn2+) of the bacterial cell<ref name="Behr and Vogel, 2010"> [http://aem.asm.org/content/76/1/142.short Behr and Vogel, (2010)] </ref><ref name="Schurr et al, 2015"/>. Iso-α-acids or humulinic acids passing into the cell, form complexes with Mn2+ and transfer electrons out of the cell<ref name="Behr and Vogel, 2010"/>. By targeted molecular modifications [http://www.sciencedirect.com/science/article/pii/S0740002014002470 Schurr et al. (2015)] determined that the Mn oxidative stress-driven antimicrobial effect of iso-α-acids was more important than antimicrobial effect of the ionophore proton transfer discussed above in the overall antimicrobial activity of hops<ref name="Schurr et al, 2015"/>.