Understanding Wet Hop Ales Part 1 – Essential Oils

Lately I’ve been a little obsessed with wet hop ales, beers brewed with freshly picked hops that go straight from hop bine to brew kettle. My curiosity was piqued back in late July when I visited Zachrich Hop Farm near Mechanicsburg, Ohio. They were having an open house and had invited members of the SODZ Homebrew Club out to pick some hops and brew a wet hop ale with hand-picked Centennial hops. A few weeks later I harvested the hops grown in my yard and brewed my own wet hop pale ale. Visually it’s hard to beat the appearance of adding copious amounts of freshly picked, bright green hops to the wort, but if I’m honest I have to admit I’m never really satisfied with the hop character in my own wet hop ales. That’s not the experience I have with growing fruits and vegetables in the garden. No one ever says, my tomatoes were pretty good this year, but not as flavorful as the ones I picked up at the grocery store. My faith in wet hop ales was restored by the good folks at Columbus Brewing Company, who released a stunning eight different wet hop ales this year, featuring hops from Oregon, Washington and Michigan.

These events have raised some questions in my head. What exactly are the characteristic features that set wet hop ales apart from conventional hop-forward beers? Can wet hop ales made with Midwestern hops match those made from Pacific Northwest hops, and if so does the local terroir express itself? Finally, how can I up my game so that my wet hop ale is the best possible beer? This is the first of three posts where I do my best to tackle these questions. Homebrewers and amateur hop gardeners like myself are the primary audience, but hopefully anyone who enjoys a good hoppy beer can learn a few things along the way.

Freshly harvested Centennial hops from Zachrich Hop Farm.

What are the Defining Characteristics of a Wet Hop Ale

From a process perspective it’s easy to define a wet hop ale. At some point in the brewing process the brewer must use whole cone hops that have not been dried or processed. Because wet hops degrade very quickly there is a narrow window of time to use the hops. A few hours is best, but if the distance between the hopyard and brewery is substantial (Columbus is >2000 miles away from hop fields of the Pacific Northwest) the window can be stretched out to something like 24-36 hours if the hops are refrigerated during transport. Most people would agree that not all of the hops used in the beer have to be wet hops. Over the past 10-15 years the brewing community has learned that it doesn’t make a lot of sense to use wet hops for bittering. Not only does the boil drive off the precious volatile substances that you are working so hard to put into the beer, it can lead to extraction of unwanted vegetal flavors.  

From a sensory perspective it’s a little more nuanced to describe a wet hop ale. In a blind taste test how would you instruct someone to identify a wet hop pale ale or IPA? To answer this question, I sought input from a few experts on the topic.

In his book, “The Secrets of Master Brewers” Portland-based beer writer Jeff Alworth sums it up as follows “These (wet) hops suffuse the beer with qualities unavailable to the brewer using dried hops: vivid, almost electrified, perfumy aromas and flavors as intense as ripe fresh-picked fruit or flowers. When they work, fresh-hop ales are among the most satisfying beers in the world. When they don’t, they can taste vegetal or even evoke overripe compost.”  

When I asked Tony Corder, Director of Innovation at Columbus Brewing Company, to describe the characteristics of a wet hop ale he put it this way. “In addition to aroma intensity, wet-hop beers should have that identifiable “green,” herbal, chlorophyl-like character. The Brewers Association even goes as far to describe it in their style guidelines as “exhibiting green grass-like, fresh mown hay/grass or other fresh hop attributes.” Ideally, we’d hope that those herbal characteristics remain fresh and pleasant, while still showcasing the aromas a particular hop is known for.

I put the same question to Sean White, co-owner of Little Fish Brewing in Athens, Ohio. His response speaks more to the romance of a making a wet hop ale than to specific aromas and flavors, but I think his comments are instructive to understand the allure of this ephemeral style. “I love the tradition of making wet hop beers, and it invokes a strong nostalgia for earlier days when I was just getting started brewing out in Portland Oregon. My friends and I would regularly attend fresh hop festivals in Portland and Hood River (my favorite festival in an amazing little town, in the pristine nature of the Columbia River Gorge).  There was also a great homebrewers’ event, “Hop Madness”, where we went to Salem Oregon, camped out, toured a hop farm and processing center, and brewed wet-hop beers at the campground.  The wet hop tradition for me is about camaraderie, about nature, and getting to the fun and the social aspect of craft beer.  I wanted to continue that tradition when we started our own brewery and bring some of that spirit to Ohio.

Essential Oils – A Primer

To understand why wet hop ales taste different than beers made with processed hops one has to have a rudimentary understanding of the compounds in hops and what they bring to a beer. From a brewing perspective the important elements are the acids and essential oils, both found in the yellow resin produced by the lupulin glands. Alpha- and beta-acids are responsible for the bitterness that balances the sweetness of the malts, while essential oils add aroma and flavor. When thinking about wet hop beers we’ll focus our attention on the latter group.

Essential oils make up only tiny fraction of the lupulin (1-4% by mass), but they are responsible for all of the aromas you associate with hoppy beers—fruity, piney, juicy, herbal, dank, tropical, juicy, etc. Scientists have identified over 400 different aroma compounds in hop oils, and not everything about how they shape your perception of a beer is fully understood. To simplify things I’m going to follow the lead of Scott Janish, author of “The New IPA”, who classifies essential oils into three categories: hydrocarbons, oxygen-containing compounds, and sulfur-containing compounds.

Hydrocarbons make up the largest fraction of the oils, 40-80% by mass, and the American hop varieties usually featured in wet hop ales tend toward the higher end of this range. While they are the most concentrated of the three broad families of essential oils they are also the least soluble in water.  To understand why we need a short primer on solubility.

The electrons that hold the hydrogen and oxygen atoms together in H2O are not equally shared. Oxygen exerts a much stronger pull on those electrons and in doing so the oxygen end of the molecule picks up a partial negative charge while the electron deficient hydrogen atoms become positively charged. Overall the water molecule is neutral, but it has negatively and positively charged regions. Chemists refer to molecules like this as being polar.  Carbon and hydrogen have a more communal approach to bonding, sharing the electrons equally. Consequently, there are no charged regions in a hydrocarbon molecule and these molecules are classified as nonpolar. Polar and nonpolar molecules don’t stick to each other very well. That’s the reason why oil (another hydrocarbon) and water separate rather than mixing. This lack of mixing allows the hydrocarbon hop oils to escape the liquid and find their way to your olfactory receptors, contributing to the hop aroma of a beer. At the same time the highly volatile nature of these oils means that most of the molecules escape during the brewing or fermentation process and are long gone by the time you get around to raising a glass of ale to your nose.

The most prevalent compounds in the hydrocarbon fraction of the essential oils (listed in order of decreasing concentration) are myrcene, humulene, caryophyllene, pinene, and farnesene. These molecules are most closely associated with the aromas of trees and other woody, herbaceous plants. To understand them better let’s pull some descriptions from Harold McGee’s book, “Nose Dive – A Field Guide to the World’s Smells

Myrcene – Aroma descriptors include woody, resinous, green, and citrus. It contributes to the aroma of conifer trees, eucalyptus, marijuana, and citrus peel.

Humulene – Aroma descriptors include woody and hoppy. It was first isolated from hops and is also a found in marijuana.

Caryophyllene – Aroma descriptors include woody, camphoric, peppery. It is found in cloves, cinnamon, marijuana, and tulips.

Pinene – Aroma descriptors include piney, woody, and terpy. It contributes to the aroma of pine, cypress, citrus fruits, and a wide range of herbs and spices.

Farnesene – Aroma descriptors include citrus, green, herbal. It contributes to the aromas of many flowers.

Notice the kinds of aromas that come up repeatedly, conifer trees and marijuana. Looking back over my tasting notes for Columbus Brewing Company’s wet hop ales I find the aroma descriptor dank, multiple times. The seems pretty spot on for describing aromas that are a mixture of a coniferous forest and marijuana. We also see the generic “green” in more than one place, which hearkens back to Tony Corder’s description of the characteristic flavors of a wet hop ale. Though less prominent, we might expect hydrocarbon essential oils to contribute floral, herbaceous aromas as well.  

Molecules that Janish lumps into the oxygen-containing oil group contain electron hungry oxygen atoms (duh) and therefore are slightly polar leading to solubility in water that is approximately 10-100 times higher than hydrocarbons. These molecules account for 20-40% of the oils and are closely associated with floral and fruity aromas. Among the most common are the monoterpene alcohols linalool, geraniol, nerol, and citronellol. Linalool is often described as floral and sweet-citrusy. This molecule is found in a staggering 75% of all flowers. Linalool makes important contributions to both coriander and lavender. Aroma descriptors for geraniol, nerol, and citronellol include floral, rose, geranium, and citrus. While not overly fruity themselves these molecules can undergo reactions in the boil and fermentation that lead to molecules like esters and aldehydes that are responsible for fruity aromas.

Sulfur-containing oils are only present in small amounts—less than 1% of the total oil content—but they are potent aroma molecules that can have an outsized impact on your perception of a beer. In minute quantities they add fruity aromas that are often described as tropical—passionfruit, mango and sauvignon blanc grapes. As their concentration increases sulfur-containing thiols can lead to unwanted aromas like onion, garlic, and catbox. More closely associated with southern hemisphere hops it’s not clear how big of a role they play in Northern Hemisphere wet hop ales.

Janish’s classification of hop oils is instructive for thinking about the characteristics of a wet hop ale. Because the hydrocarbon oils are so volatile it makes sense that minimizing the time between harvest and brewing would boost their presence in the finished beer (provided you add them in the whirlpool or as a dry hop addition), perhaps more so than oxygen- or sulfur-containing compounds. We should also keep in mind that as the hops age they will slowly be oxidized (like all foods, herbs, and spices), converting hydrocarbons into oxygen-containing alcohols. Based on these considerations one would expect to see a corresponding shift in the aroma balance. A good wet hop ale should have more of the piney, green, cannabis-like aromas that come from the hydrocarbons, and possibly less of the floral, fruity aromas of the oxygen-containing oils.

Molecular structures of several key essential oils found in hops.

Now that we’ve got some chemistry under our belts we are ready to put that knowledge to use. In Part 2 we take a closer look at different hop varieties, with an eye toward picking the best varieties for your home garden, and we get some tips on growing and harvesting midwestern hops from the pros at Zachrich Hops Farm. In the third and final instalment, we will put it all together to see how your average homebrewer can best utilize homegrown hops.

One thought on “Understanding Wet Hop Ales Part 1 – Essential Oils

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  1. Great research article Pat! Although a touch of onion or garlic can be pleasant on the nose, catbox is best in only the smallest of quantities. Cheers!

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