The Chemistry Of Green Hops: Unlocking The Secret Aroma

The aroma of green hops is attributed to several compounds found within the plant, including essential oils and alpha and beta acids. While many compounds contribute to the unique aroma of hops, myrcene is the most abundant oil component in most hop varieties and is responsible for a green, herbaceous, and resinous aroma. Humulene, caryophyllene, and farnesene are also present in hop oil, imparting herbal, woody, spicy, and sometimes citrus or floral notes. These compounds are highly volatile and have low solubility, meaning they are more likely to be perceived when added late in the brewing process or through dry hopping techniques.

Myrcene is the most common oil in hops, providing a green, resinous, piney aroma

Myrcene is the most common oil found in hops, providing a green, resinous, piney aroma. It is a terpene, a hydrocarbon with a low odour threshold, meaning it is highly potent. Myrcene is often found at levels of over 50% of all available hop oils in each hop variety. It has a distinctive aroma, described as green, herbaceous, and resinous, and is associated with fresh hops.

Myrcene is highly volatile and not very soluble, so it is perceptible in finished beer only when added very late in the boil or post-fermentation. It will be scrubbed away during boiling and fermentation but will provide a distinctive piney character to a dry-hopped beer.

The BarthHaas Group (BHG), a world-renowned hops company, introduced a uniform Sensory Language specifically for hops and hoppy beers called HOPSESSED®. Myrcene is one of the 12 aroma categories initially noted by their perfumer, Frank Rittler.

Myrcene is a key component in the distinctive aroma of hops, and its presence in high concentrations gives beer its characteristic hoppy aroma.

Humulene is the second most common oil, adding woody, spicy, and herbal notes

Humulene, also known as α-humulene or α-caryophyllene, is a naturally occurring monocyclic sesquiterpene (C15H24) and is one of the components of the hydrocarbon fraction of hop oil. It is the second most common hop oil, adding woody, spicy, and herbal notes to beer. Humulene is formed in the final stages of hop cone maturation and is found in the lupulin gland, along with other essential oils. The concentration of humulene varies among different varieties of the hop plant but can be up to 40% of the essential oil.

Humulene is highly volatile and hydrophobic, meaning that only trace quantities may reach the final beer. However, its oxidation products, particularly humulene mono- and di-epoxides, can impart significant amounts of aroma to the beer. Humulene epoxide III, for instance, is one of the most potent flavour compounds in Hallertauer Mittelfrüh, a variety that is high in humulene but relatively low in total oils. Brewers have found that allowing hops that are high in humulene to age in bales for several weeks before pelletizing increases the amount of humulene epoxides and other hop oil oxidation products, which can significantly enhance the aroma potential.

Humulene is also found in many other aromatic plants, including pine trees, orange orchards, tobacco, and sunflower fields. It is contained in the essential oils of plants such as common sage, Japanese spicebush, ginseng species, and the ginger family. Humulene is one of the chemical compounds that contribute to the taste of Vietnamese coriander and the characteristic aroma of cannabis.

Caryophyllene is an oil that adds black pepper, spiciness, and herbal flavours

Caryophyllene is a natural bicyclic sesquiterpene, a common compound found in many essential oils, including clove oil, rosemary, and hops. It is also found in spices such as black pepper, basil, and oregano, and is responsible for the slight pungency associated with smelling cracked pepper. Caryophyllene is typically 5-20% of all oils in a particular variety of hops.

Caryophyllene is also known as beta-caryophyllene or BCP. It is notable for its chemical structure, which includes a cyclobutane ring and a trans-double bond in a 9-membered ring, both of which are rare in nature. Caryophyllene is one of the chemical compounds that contribute to the aroma of black pepper.

In hops, caryophyllene is an essential oil that adds black pepper, spiciness, and herbal flavours to beers. It is the second most abundant hop oil, after myrcene, and it contributes woody, hoppy, and spicy notes to beer. The amount of caryophyllene in hops can vary depending on the variety and growing conditions.

The human body's endocannabinoid system contains CB2 receptors, primarily located in peripheral organs. Caryophyllene has the unique ability to bind to these receptors, providing potential medical benefits without causing any euphoric effects. Studies have shown that caryophyllene has anti-inflammatory, antioxidant, antimicrobial, and insecticidal properties. It has also been shown to have pain-relieving properties and the potential to reduce alcohol intake, making it a possible treatment for addiction.

In addition to its therapeutic benefits, caryophyllene is used as a food additive, typically for flavouring. It has been designated as generally recognized as safe (GRAS) by the FDA, and rats given up to 700 mg/kg daily for 90 days showed no significant toxic effects.

Farnesene is an oil that adds fresh, green, and woody aromas

Farnesene is highly volatile, like the other essential oils found in hops. This means that it evaporates quickly if left in the boil for too long. To capture the fresh, green, and woody aromas of farnesene, brewers must add the hops late in the boil or use the dry hopping technique, which involves adding hops to the fermenter after the yeast has already started to work.

The concentration of farnesene in hops is usually very low, ranging from a trace amount to 1%. The ratio of caryophyllene to humulene and the presence or absence of farnesene are considered characteristic markers for different hop varieties.

While farnesene is responsible for the fresh, green, and woody aromas, other compounds in hops contribute to the overall flavour of the beer. Hops contain organic compounds called alpha and beta acids, which provide bitterness. Beta acids, in particular, contribute to a harsher bitterness than alpha acids. Essential oils from the hops are responsible for the bulk of the aroma and flavour, with over 250 different essential oils identified in hops.

Linalool and geraniol are the two most abundant terpene alcohols, adding floral and citrus notes

Linalool and geraniol are terpene alcohols that are commonly found in many essential oils, such as citronella and thyme. They are valued for the floral and citrus notes they add to products and are therefore often used in perfumes and scents.

Linalool is a floral and orange-scented compound that is present in essential oils such as rose oxide, geranium, and orange blossom. It is also a major component of the scent of coriander. It is commonly found in hops varieties such as Amarillo, Cascade, Centennial, Citra, Glacier, Millennium, Mount Hood, Nugget, Pacifica, and Willamette.

Geraniol, on the other hand, has a rose-like scent and is a primary component of rose oil, palmarosa oil, and citronella oil. It is also found in small quantities in geranium, lemon, and many other essential oils. Geraniol is produced by honeybees to mark nectar-bearing flowers and locate their hives. It is commonly found in hops varieties including Aurora, Bravo, Cascade, Centennial, Chinook, Citra, Mosaic, Motueka, and Styrian Golding.

Both linalool and geraniol are valued for their pleasant scents and insect repellent properties. They are often used in candles, diffusers, and insect repellents, providing significant protection against mosquitoes.

While linalool and geraniol are two of the most abundant terpene alcohols, the aroma of green hops is primarily attributed to myrcene. Myrcene is the most prominent oil in hops, constituting 50% or more of the oils in hops varieties such as Cascade and Simcoe. It has a green, herbaceous, and resinous aroma, providing a distinctive piney character to dry-hopped beer.

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