13,591
edits
Changes
Hops
,no edit summary
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"/>.
Hydrocarbons, specifically terpenoids, make up the majority of hop oil. The majority of these terpenoids are myrcene, which characterizes the aroma of hops (although this compound does not carry over well into beer because it is hydrophobic), caryophyllene, and humulene. Most of these compounds are evaporated off by the brewing process, and others are metabolized into different compounds during fermentation <ref name="Kishimoto_2008">[https://www.ncbi.nlm.nih.gov/pubmed/18173243 Comparison of 4-Mercapto-4-methylpentan-2-one Contents in Hop Cultivars from Different Growing Regions. Toru Kishimoto, Minoru Kobayashi, Nana Yako, Ayako Iida and Akira Wanikawa. 2008.]</ref>. Linalool (citrus, floral) and geraniol have been identified as the major compounds that contribute to beer flavor in hop varieties such as Cascade <ref name="Kiyoshi_2009" />.
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>.