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The main compounds of interest to brewers in hops are their bitter acids and oilscontained in the yellow-colored lupulin glands. There are at least 250 significant aroma and flavor compounds found in hop acids and oils. Alpha acids account for roughly 2-17% of dried hops by mass, beta acids account for roughly 2-10%, 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 rest of the weight of hops is made up of 40-50% cellulose and lignin, 15% protein, 8-12% water (after drying), 8% minerals, 3-6% polyphenols and tannins, 1-5% lipids and fatty acids, 2% monosaccharides, and 2% pectin <ref name="Algazzali_2014">[The Bitterness Intensity of Oxidized Hop Acids: Humulinones and Hulupones. Victor Alexander Algazzali for the degree of Master of Science in Food Science and

The primary '''alpha acids''' (humulones) 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 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 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<ref name="Schönberger and Kostelecky, 2012"/>. Alpha acids are susceptible to oxidation and the alpha acid content of a hop will decrease with storage.

'''Beta Acids''' (lupulones) are similar in structure to alpha acids and have the analogous individual beta acids (lupulone, colupulone, adlupulone) to individual alpha acids. Beta In their original form, beta acids do contribute to the flavor of beer. They are also not able to isomerize and are therefore not soluble in wort unless they are chemically modified by a process such as oxidation<ref name="Algazzali_2014">. Oxidatized beta acids are soluble and can contribute to bitterness in beer. Oxidized beta acids are discussed more under aged hops.

In [[lambic]] brewing, '''aged Aging hops''' refers leads to hops that have been aged for 2+ years in non-refrigerated conditions, oxidation of acids and in burlap sacks or some other oxygen permeable bag <ref>[http://jesterkingbreweryoils.com/home-for-our-aged-hops "Home for Our Aged Hops". Jester King's blog. Retrieved 11/18/2016.]</ref>. It should also be noted that "aged hops" can refer Generally brewers seek to avoid this to any sort preserve the aromatic and bittering properties of hop aging (especially their hops by freezing them and storing them in scientific literature)vacuum sealed packaging; however some beer styles, including short term hop aging (1-6 monthslambic and historical styles, for example) in refrigerated or non-refrigerated temperatures. Much make extensive use 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 Aged hops that are still retain some antimicrobial properties and can be used in lambic brewing or similar beers might have different effects than what has been studied in for microbial inhibition. In addition to their antimicrobial activity aged hops that are aged for shorter periods of timecontribute important flavor and aroma compounds and precursors to beer.

Aging In [[lambic]] brewing, '''aged hops leads ''' refers to oxidation of acids these hops which have been aged for 2+ years in non-refrigerated conditions, and oilsin burlap sacks or some other oxygen permeable bag <ref>[http://jesterkingbrewery. Generally brewers seek 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 avoid this to preserve the aromatic 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 bittering properties in oxygen rich or vacuum sealed packaging. Much of their the information below references hops; however some beer styles make extensive use of that have been aged in warm conditions for shorter time periods than what hopsare aged for in lambic brewing. Aged The additional aging of hops still retain some antimicrobial properties and can be that are used in lambic brewing or similar beers might have different effects than what has been studied in hops that are aged for microbial inhibition. In addition to their antimicrobial activity aged hops contribute important flavor and aroma compounds and precursors to beershorter periods of time.

During aging, both alpha and beta acids oxidize and degrade with warmer temperatures and more oxygen exposure having a greater impact. The generally accepted theory is that oxygen interacts directly with hop acids. This event is called "autooxidation". An alternative theory to this is that oxygen indirectly oxidize acids by first oxidizing the hop oils and turning them into pro-oxidants, which then oxidize the hop acids which are mixed in with the oils within the lupulin glands <ref name="Algazzali_2014">. This oxidation of hop acids corresponds with an increase in the [http://methods.asbcnet.org/summaries/hops-12.aspx Hop Storage Index (HSI)], which is a practical way of measuring the overall freshness of hops. As the oxidation of hop oils rises, the measured HSI number on a lot of hops increases <ref name="Lam et al., 1986"/><ref name="Maye_2016">[http://www.hopsteiner.com/wp-content/uploads/2016/07/TQ-53-1-0227-01.pdf Humulinone Formation in Hops and Hop Pellets and Its Implications for Dry Hopped Beers. John Paul Maye, Robert Smith, and Jeremy Leker. 2016.]</ref>. These oxidized compounds lead to a higher amount of non-alpha-acid bitterness compounds in aged hops, and have a remarkable effect on the bitterness of beer. The bitterness from oxidized hop compounds has been described as more earthy, harsh, and astringent than the sharper, cleaner bitterness from iso-alpha acids <ref name="Mikyška_2012">[http://onlinelibrary.wiley.com/doi/10.1002/jib.40/abstract Assessment of changes in hop resins and polyphenols during long-term storage. Alexandr Mikyška and Karel Krofta. 2012.]</ref>.