You don’t need inside knowledge to know that hoppy beers are hyper-trendy these days. The demand seems inexhaustible. In the U.S., “Gimme an IPA” has replaced the more generic bar call for “a beer.” There are white, black, red, double, triple, session and Belgian variations, all slurped up eagerly. With so much hoppy liquid moving across people’s lips, it seems like a good time to dig into the hop’s diverse flavors and hopefully enrich your experience.
Hops as an ingredient in beer have a documented history going back 2,500 years. By 1500 they were the dominant seasoning in nearly every European brewing tradition. And why not? Hops bring a range of pleasant botanical aromas, bitterness to balance the sweetness of malt and even a protective effect against some common beer spoilage bacteria. While there is a lot of fabulous hop lore, history and botany, I’m going to skip it and jump right into vocabulary, because, well, it’s complicated.
Unlike the easy, food-based vocabulary we use to describe malt, hop aroma is challenging to wrap your head around; coming up with the right language is even more so. Hops contain several hundred aromatic chemicals; the specific mix in any hop determines its overall aroma. Many of these chemicals are found in citrus fruits, spices and other herbs, so there’s some vague familiarity, but the particular combination often defies precise description. So we struggle along with vague words like “herbal,” citrusy” and “spicy,” a term that has nothing to do with any actual spice but is a code word for “hoppy.”
With each hop showing a unique spectrum of hundreds of aromatic oils that vary by variety, location, year and other factors, it’s crazy complicated. These oils interact in surprising ways, masking or enhancing one another, and they are also chemically active, interacting and transforming during brewing and fermentation. The net aroma is definitely more than the sum of its parts. Human noses are amazing, having recently been shown to be capable of discriminating among at least a trillion different aromas. Naming them, however, is another matter. The best we can do is shoehorn our impoverished vocabulary into this rich sensory experience.
“Herbal” is a common hop descriptor and suits hops like the German Hallertau Mittelfrüh, with notes of bay, thyme and possibly mint. “Citrus” is a vague but accurate descriptor. Grapefruit may be found in many American West Coast hops, and some newer varieties like Mandarina Bavaria and Lemondrop are built around specific citrus aromas. The shared terpene chemicals limonene and linalool bring citrus notes, along with beta-citronellal, an aldehyde. Nerol was first isolated from orange blossoms, so it brings both orange peel and blossom notes. Floral aromas are also common in American hops, most notably Cascade, which has a good quantity of geraniol; farnesene also brings floral qualities as well as herbal and woody notes. It should be noted that while the oils I mention here are among the most bountiful, there are many other flavor-active ones. In fact, untangling how chemicals combine to create specific hop aromas is still very much a work in progress.
There’s pine and resin, too, and even a quality called “dank,” a reference to marijuana, a close hop relative. Both plants share an abundance of myrcene, which is described with a variety of terms: resinous and piney, but also peaches, vanilla, balsamic, woody, green, herbaceous and peppery. That a single chemical can have so many descriptors testifies to the shortcomings of language when it comes to aroma.
Finally, there are some hops that simply smell hoppy, with no other culinary overtones. Saaz and its many relatives are often described as “spicy,” but no one can say which spice. I love a hop called Glacier, but I have been utterly unable to find a more complete description than “clean and hoppy.” So even though it sounds pretty vague, “hoppy” really is a useful term in our aroma vocabulary, since it often fits where no other word will serve.
Recent breeding efforts have put the spotlight on a group of sulfur-containing chemicals called thiols that have a lot of exotic fruity notes: berry, passion fruit, mango, melon and more. They are present in minute quantities, but like many sulfur compounds, they are very intense. They may also change character as their intensity increases; many pleasantly fruity aromas turn to cat pee when above a certain threshold.
And as much as we love the pleasant aromas hops can bring to our beer, it’s not all good. Hops also have some challenging aromas. Along with the catty notes already mentioned, thiols are also responsible for aromas of toasted onion or garlic, often characterized as onion bagel. This oniony aroma is common in a number of newer hops, especially Summit. Depending on the year and the specific lot, the beloved Citra displays a good deal of this alongside its namesake aromas.
Poor storage of hops can result in cheesy aromas from isovaleric acid. And in a beer, hops may deteriorate unpleasantly; many hoppy beers display a strong blackcurrant/grape aroma from a compound called beta-damascenone. In combination with too-alkaline water chemistry, hops may also present harsh, astringent notes on the finish of the beer.
Now it gets weird.
Our brains create a phantom sense called flavor, a synthesis of aroma, taste, mouthfeel and other input from our eyes, memory and more. Flavor also incorporates what are called retronasal olfactory sensations: aromas perceived not through the nostrils, but those that travel up from the back of the mouth and throat. In addition to being a grand combination of senses perceived as a single thing, retronasal also takes advantage of some chemistry that’s going on in our mouths.
Enzymes in our saliva and similar ones oozing from the many microbes that live in our mouths can break down molecules known as glycosides. These consist of a molecule of some sort bound to a sugar. In the case of aroma molecules, this binding makes them nonvolatile, meaning hop aroma glycosides can go through brewing and fermentation without evaporating, as a large fraction of normal hop oils do. When the glycosides hit the enzymes, the aroma molecules are released, becoming volatile aroma compounds we can experience in the retronasal.
When it comes to hop bitterness, there’s nothing subtle or challenging about describing it. It sears your tongue with dread or delight, increasing slowly and hanging on when everything else is gone. The evolutionary history of our 26 bitter receptors is astonishingly complex, but one important role is to warn of potential toxins in our environment. As a result, bitterness is the only one of the basic tastes that we are predisposed to reject. Additionally, there is a genetic variation that makes 20 percent of the population hypersensitive to bitterness, which might be the reason that your significant other won’t ever be able to share your abiding passion for hoppy IPAs.
Bitterness may be psychologically complicated, but from a chemical and vocabulary view, it’s pretty simple. Hop bitterness comes mainly from a group of chemicals known as alpha acids that are chemically transformed—isomerized—during wort boiling, becoming bitter and soluble. Because we have many different bitter receptors, bitterness itself comes in many shades. Hops give a soft, mellow bitterness, especially when compared with the dry, piercing bitterness of botanicals like gentian or wormwood. In beer, the only variation of bitterness is intensity.
One interesting side note is that these alpha acids have psychopharmacological effects, supporting the hop’s long history as a sleep inducer. One alpha acid in particular, methyl-3-buten-2-ol, has been shown, at least in animals, to inhibit the brain’s GABA neurotransmitter system and promote sleep. So is it possible in this age of turmoil that we are all self-medicating just a little with the current mad abundance of IPAs?
Hops are just one ingredient. But with their complex chemistry, botanical variations, response to the place they’re grown and the way they’ve been cared for, hops in beer are anything but simple. Pay attention to their subtleties and every sip will open up a whole universe of flavor for you.
Randy Mosher is the author of Tasting Beer and is a senior instructor at the Siebel Institute.