This week I take a fresh look at the major aromatic hop oils and how they affect your beer’s aroma and flavors.
Aromatic Hop Oils
Hops contain over 500 flavor and aroma compounds, many of which are transformed during brewing fermentation and aging. In addition, when and how you use the hops can affect the flavors produced. Several weeks ago I wrote an article on Hop Alpha Acids, which covered the five major alpha acids that contribute the bulk of the bitterness to your beer, primarily through boiling or a hot steep.
This week I’ll focus on aromatic oil compounds that, instead of bitterness, produce a wide variety of hoppy aroma in a finished beer that vary from tropical to piney to spicy. These aromas, combined with bitterness from the boil addition give you the complete hoppy sensory experience you get when you sample a well made IPA. Scott Janish has a nice interactive chart here that shows hop oil concentration for most of the major hop varieties and this is a handy tool for those looking to learn more.
Most aroma oils are volatile, meaning they vaporize at a fairly low temperature, which is why whirlpool and dry hopping have become the preferred way to introduce them into a beer.
Major Hop Oils
Here are the major hop oils that provide the bulk of the aroma in a finished beer:
- Myrcene – The most significant hop oil, making up from 30-60% of total hop oils in most varieties. Myrcene is often described as the “fresh hop oil” and has flavors and aroma varying from herbaceous to resinous, green, balsamic, and slightly metallic. It is a major component in many hop varieties from the Pacific Northwest, and is therefore a critical oil in IPAs. Cascade, for example has a myrcene content of nearly 60%. Myrcene has a low boiling point and is highly volatile. In fact it will virtually disappear in most boil additions, and even tends to be volatile in higher temperature whirlpool/steeping additions. It also oxidizes very rapidly, and is probably best used in dry hop applications.
- Humulene – The second largest hop oil by percentage, humulene makes up between 12% and 50% of total hop oils. Humulene is responsible for earthy and spicy flavors found in traditional noble hops. While humulene has a higher boiling point (around 210 F or 98.9 C), it is very volatile and hydrophobic, so it is still best used in the whirlpool or dry hopping. Humulene is also easily oxidized, though the oxidized humulene-epoxide III play a major role in the flavor of varieties like Hallertauer Mittelfrüh.
- Caryophyllene- Caryophyllene makes up between 6% and 15% of total hop oils in most varieties. It is a major compound in many aromatic plants including cloves, cannabis, rosemary, and hops. It is also a significant aromatic compound in black pepper. The aroma is described as woody, earthy, and peppery though it also has a strong herbal component. The spicy, woody aroma is often evident when you crush dried hops in your hands. Many English hop varieties such as East Kent Goldings have the largest percentage of caryphyllene giving them a woody, earthy finish. While not quite as volatile as myrcene, caryophyllene it will boil quickly and is best used in the whirlpool or as a dry hop.
- Geraniol – Geraniol is an aromatic oil with a floral, sweet or rose aroma found in many American, New Zealand and Australian hops. It is used in rose oil, palmarosa oil, and citronella oil, and is a component of common spices like lavender, nutmeg, coriander, rose and blackberry. Many brewers also will add hops with geraniol during the tail end of active fermentation to promote tropical and citrus fruit flavors. Hops with high geraniol have become popular for creating tropical/fruity IPA styles.
- Linalool – Related closely to Myrcene chemically, linalool has a floral aroma that smells like rose, orange, citrus or lavender. It is more soluble in wort than myrcene, and also has a lower flavor threshold so it can be potent despite the small fraction it makes up of total hop oils. Like geraniol, linalool is associated with many of the tropical, floral and citrus flavors that are popular in fruity and tropical IPAs.
- Farnesene – Farnesene is a volatile hop oil that is loosely associated with certain noble hops like Saaz, but can make up 10-20% of total hop oils in other noble hops like Tettnanger, Styrian hops and many American varieties. It has a woody, herbal, citrus aroma and sometimes also takes on a floral character. Because it is very volatile, it is rarely found in the finished beer unless it has been dry hopped. The compounds is often associated with varieties that take on a noble hop character, so if you see a hop high in Farnesene it likely has the aroma profile similar to many noble hops.
- β-Pinene – Though not a major hop oil, β-Pinene has a green-woody and piney aroma. It is a monoterpene, commonly found in many plants and it is soluble in alcohol but not water.
- Thiols – Fully covering thiols and their role in brewing could easily fill several articles. Thiols make up a very tiny fraction of overall hop oils, but are potent aromatics and also can biotransform and enhance many other hop oils in positive ways. They can drive beer flavor in both a positive and negative way but the most flavor positive thiols are 3MH, 4MMP (4-methyl-4-mercaptopentan-2-one), 3MHA (3-mercaptohexylacetate), and 3S4MP (3-sulfanyl-4-methylpentan-1-ol). Flavors associated with these include tropical fruits, passion fruit, grapefruit, rhubarb, black currants, and wine flavors. Thiols are so important to many IPA styles that labs have developed thiol boosting yeasts and additives to free bound thiols from hops. I’ve done several podcasts on thiols including this one with Stan Hieronymus and this one with Morebeer if you want to learn more.
Those are the most important hop oils, and as mentioned above, you can find the interactive chart of hop oils for many varieties from Scott Janish here. I hope you enjoyed this week’s article on hop oils! Thank you for joining me on the BeerSmith Home Brewing Blog. Be sure to sign up for my newsletter or my podcast (also on itunes…and youtube…and streaming radio station) for more great tips on homebrewing.
