Changes

There are three primary classes of '''oils''' 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 not well understood. For example, only recently it has been shown that the amount of hop oils does not correlate to hop aroma intensity when dry hopping, but the composition of hop oils does <ref name="Sharp_Presentation">"Recent Advances in Controlling Hoppy Aroma in Beer." Daniel C. Sharp. OSU Brewing Science Presentation.</ref>. 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"/>.

Hop oil contains a small percentage (~1%) of sulfur related compounds (thiols, sulfides, polysulfides, thioesters, thiopenes, and terpene derivatives). Although these levels are low, the flavor thresholds for these compounds also tends to be very low. Hydrogen sulfide can be released from these compounds during fermentation. Hops that have been treated with sulfur to prevent mildew growth (an older process that is generally no longer used) can result in increased sulfur compound such as sulfuric terpenes, and lend a garlic-like aroma in beer. Few sulfur compounds survive boiling, however late hopping and dry hopping preserves more sulfur compounds which can survive into the beer. Fermentation generally volatilizes sulfur compounds, and some are volatilizes out almost completely <ref name="Peppard_1981">[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1981.tb04054.x/abstract VOLATILE ORGANOSULPHUR COMPOUNDS IN HOPS AND HOP OILS: A REVIEW. T.L. Peppard. 1981.]</ref>.

Other thiol (organic sulfur) based compounds contribute to a pleasant aroma and flavor in beer, such as 4-mercapto-4-methyl-pentan-2-one (4MMP), which is found in high quantities in North American varieties such as Simcoe (highest amount), Summit, Apollo, Topaz, and Cascade hops, as well as varieties from Australia and New Zealand. The character of black currant, muscat-like aroma in beer brewed with these hops has been attributed to 4MMP. It is thought that 4MMP is only found in North American, Australian, and New Zealand hops and not European hops because European hops are often treated with copper ions, which has been shown to decrease the amount of 4MMP in hops. Interestingly, beers brewed with these hops showed a 33% increase in 4MMP after fermentation; it is thought that the precursor cysteine conjugate is responsible for the increase in 4MMP during fermentation <ref name="Kishimoto_2008" />. The volatile thiols 3-sulfanyl-4-methylpentan-1-ol (3S4MP), and 3-sulfanyl-4-methylpentyl acetate (3S4MPA) have been identified in Nelson Sauvin hops as the compounds that give these hops their "wine-like, Sauvignon Blanc" character. Similar thiols have been described as the major contributors to the aroma of Sauvignon Blanc wines themselves: 3-sulfanylhexan-1-ol (3SH) and 4-methyl-4-sulfanyl-

pentan-2-one (4MSP) <ref name="Kiyoshi_2009">[http://pubs.acs.org/doi/pdf/10.1021/jf8034622 Identification and Characteristics of New Volatile Thiols Derived from the Hop (Humulus luplus L.) Cultivar Nelson Sauvin. Kiyoshi Takoi, Marie Degueil, Svitlana Shinkaruk, Cécile Thibon, Katsuaki Maeda, Kazutoshi Ito, Bernard Bennetau, Denis Dubourdieu and Takatoshi Tominaga. 2009.]</ref>.

==Antimicrobial Properties==