Changes

The main compounds of interest to brewers in hops are their bitter acids and oils. Alpha acids account for roughly 2-12% of dried hops by mass, beta acids account for roughly --- % and oils account for roughly 0.5----3%, 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 acids are insoluble in wort, the isomerized acids which are formed during boiling are soluble. Isomerized Alpha acids themselves do not taste bitter, but 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, but studies of taste perception of individual iso-α-acids have not agreed with this (---source---). However Isocohumolone 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. Iso-α-acids are susceptible to oxidation and the iso-α-acid content of a hop will decrease with storage.

There are three primary classes of '''Oilsoils'''in hops: hydrocarbons (~64% of the total oils), oxygenated compounds (~35% of the total oils), and sulfur compounds (≤1% of the total oils)<ref name="Shellhammer, Vollmer and Sharp, CBC 2015"> Shellhammer, Vollmer, and Sharp. Oral presentation at the Craft Brewers Conference, 2015. </ref>. individual flavor and aroma active oils each have different thresholds, solubilities, and volatilities, and individual oils can have synergistic interactions with each other. The chemistry of hop oil taste perception is therefore very complicated and overall is only While sulfur compounds make up only a very small fraction of the total oils, they have a significant impact on hop flavor<ref name="Shellhammer, Vollmer and Sharp, CBC 2015"/>.

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; however some beer 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, including bitterness from oxidized alpha and beta acids.