Hop Oils
Hops Oils 101
Those compounds classified as hydrocarbons are highly volatile, not very soluble, and are perceptible in finished beer only when added very late in the boil or post-fermentation. Myrcene is almost always the most prominent, constituting 50 percent or more of the oils in hops varieties such as Cascade and Simcoe. It has a green, herbaceous, and resinous aroma associated with fresh hops that will be scrubbed away during boiling and fermentation but that will provide distinctive piney character to a dry-hopped beer.
The oxygenated hydrocarbon compounds are more soluble and aromatic. Their aromas, or new ones resulting from the fermentation process, are more likely to show up in finished beer. They include linalool, geraniol, citronellol, and hundreds of other compounds. The most prominent of them will constitute less than 1 percent of the hops oils.
Thirteen Hops-Odor Compounds to Know
- caryophyllene » woody
- citronellol » citrusy, fruity
- farnesene » floral
- geraniol » floral, rose, geranium
- humulene » woody, piney
- limonene » citrusy, orange
- linalool » floral, orange
- myrcene » green, resinous, piney
- nerol » rose, citrusy
- pinene » spicy, piney
- 3-mercaptohexanol » guava, tropical
- 3 mercaptoheyl acetate » muscat, passion fruit
- 4-mercapto-4-methyl-pentan-2-one » black currant, tropical
Hops by Compound
- Geraniol-rich Hops
- Aurora, Bravo, Cascade, Centennial, Chinook, Citra, Mosaic, Motueka, Styrian Golding
- Linalool-rich Hops
- Amarillo, Cascade, Centennial, Citra, Glacier, Millennium, Mount Hood, Nugget, Pacifica, Willamette
- Hops that Contain 4-mercapto-4-methylpentan-2-one (4MMP)
- Apollo, Cascade, Centennial, Citra, Chinook, Cluster, Equinox, Mosaic, Simcoe, Summit
https://beerandbrewing.com/hops-oils--aroma-uncharted-waters/
Terpenes
Many different terpenes are found throughout the plant world. Terpene is a general term describing compounds made of one or more isoprene groups (C5H8) (Qian, 2013). Hop analysis typically focuses on mono- and sesqui- terpenes, which consist of 2 and 3 isoprene groups, respectively.
Farnesene:
- A sesquiterpene exhibiting a noble and woody aroma profile. Interestingly, farnesene is only found in trace amounts in most modern varieties, and some actually have no detectable farnesene. Most of the varieties containing high levels of farnesene are traditional European varieties.
Hydrocarbons
- As the name implies, ‘hydrocarbon’ can describe any compound that is made up of only hydrogen and carbon atoms. While all terpenes are hydrocarbons, not all hydrocarbons are terpenes.
Monoterpenes
- Hydrocarbons made of 2 isoprene units. All monoterpenes are made of 10 carbon, and 16 hydrogen atoms (C 10H16). The most common hop monoterpenes are myrcene and β-pinene. Monoterpenes are very volatile and will usually not survive when added in hot-side additions.
Myrcene
- A monoterpene, usually the largest component of a hop’s ‘total oil’ (up to about 75%, although some varieties have significantly less). Myrcene is extremely volatile, and while it contributes heavily to raw hop aroma, it will generally not survive the brewing process due to low solubility. Myrcene has an herbal, woody, and somewhat carrot-like aroma.
Sesquiterpenes
- Hydrocarbons made of 3 isoprene units. All sesquiterpenes are made of 15 carbon, and 24 hydrogen atoms (C 15H24). The most common hop sesquiterpenes are β-caryophyllene, farnesene, and α-humulene. Like monoterpenes, sesquiterpenes are very volatile, and will usually not survive when added in hot-side additions.
Terpenes
- A class of compounds that consist of varying quantities of isoprene units (C5H8). Typically representing a large portion of the ‘total oil’ fraction of a hop, with the monoterpene myrcene usually being the most prevalent.
α-humulene
- A sesquiterpene exhibiting grassy, herbal, and woody aromas. It is highly volatile and generally will not survive the brewing process.
β-pinene
- A monoterpene, β-pinene smells pine-like. It is far less abundant in hops than myrcene, making up only about 1% of the total oil, maximum. Like myrcene, β-pinene is very volatile, and will only transfer to beer during dry hopping.
β-caryophyllene
- A sesquiterpene with a very woody aroma, sometimes cedar-like. Other aroma notes include floral and spicy. β-caryophyllene contributes to the character of noble hops and is found in lower levels in newer American hops. It generally does not survive the brewing process.
Terpene Alcohols
Terpene alcohols are closely related to terpenes. Unlike terpenes, terpene alcohols are oxygenated, making them an alcohol. By their nature, alcohols are more soluble than non-oxygenated terpenes due to their greater polarity. They therefore have a much greater retention rate into the final beer, and hops high in terpene alcohols are widely thought to benefit hot-side additions.
Terpene alcohols are also the subject of recent research investigating biotransformation. In a study by (Takoi, et al., 2012), β-citronellol, a compound not usually found in hops, was found to increase during fermentation. A prominent theory states that during fermentation certain strains of yeast are capable of metabolizing geraniol into β-citronellol, which has shown to amplify citrus/floral aroma profile in final beer. Enough geraniol must be present in the wort solution for conditions to favor this action.
Geraniol
- Like linalool, geraniol is a monoterpene alcohol which commonly survives late boil and whirlpool additions. Its aroma profile is geranium-like and citrusy. Geraniol is thought to be at least partially biotransformed by certain strains of yeast into β-citronellol during fermentation.
Linalool
- A monoterpene alcohol commonly used as a fragrance and flavoring in cosmetics and candy. It has a strong fruity and floral aroma, commonly described as similar to the aroma of Froot Loops™ cereal. High levels of linalool can act as a ‘booster’ to increase fruity flavor in beer. Linalool is beer-soluble and commonly survives the brewing process.