All About Hops
By David Nilsen
We recently talked about the basics of malt and malt enzymes as we walk through the foundational ingredients of beer, and today we're going to take a look at hops!
Hops are the primary seasoning agent in beer, and even though they look like little leafy green pine cones, they’re actually flowers. The hops we use in brewing are the female flowers of the Humulus lupulus plant—a species we believe evolved about 6 million years ago in China—and they thrive today from about 30-52° latitude north and south of the equator. For our chocolate lovers out there, cacao grows in a band 20° north and south of the equator, so there is nowhere in the world hops and cacao can be grown side by side. There are, however, two countries able to grow both in different regions: the U.S. and Australia.
Hop flowers are made up of small petals that overlap like scales on a fish around a central stalk or "strig". Concealed under these petals is a waxy yellow substance called lupulin, which contains most of the good stuff we want for brewing.
Hops grow on a vertical bine (a vine, like what wine grapes grow on, grows vertically by attaching to a growing surface with tendrils or suckers, while a bine, as in the case of hops, grows vertically by wrapping its main stalk around the growing surface). In a hop yard, hops are grown on a trellis system of wooden poles connected by strings and wires. Hops grow rapidly and aggressively during the growing season—their Latin name translates into small wolf—reaching 18-20’ in height across the summer. They stay alive beneath the soil as rhizomes during the winter and will return again in the spring. Nothing looks quite like a hop yard in the summer, with 20’ tall hedgerows of green stacked one after the other across the field like the corridors of a gigantic maze.
After being harvested, the cones are rapidly dried to preserve them—except for a small amount that will be used in seasonal wet hop beers to show off their fresh aromas—and are then either sold as whole dried cones or processed into compact pellets for easier storage and use. Hop companies have also experimented with many other hop-derived products over the years, such as powders and extracts.
Hops provide two main attributes in beer: bitterness and aroma/flavor.
The bitterness in hops comes from alpha and beta acids. In their natural state, these acids aren’t all that bitter, and they’re not all that liquid-soluble either. Brewers unlock these bittering acids by boiling the hops in the unfermented beer. The boiling process causes the acids to isomerize, at which point they’re significantly more bitter and more liquid-soluble. Isomerization is when a molecule physically reconfigures without adding or removing molecular components. Brewers add hops early in the boil to allow these acids to isomerize.
The flavor and aromas we get from hops come from essential oils, and the concentrations and interactions of these oils can be dazzlingly complex. They are highly aromatic, which means they are also highly volatile, and the oils from the hops added early in the boil get lost in the process. Brewers add hops for aroma and flavor late in the boil, just after the boil, or even in the fermenting or conditioning beer later on. This extracts the aromatic compounds without extracting much, if any, additional bitterness.
Different hop varietals showcase markedly different aromas and flavors, and this is where hops get really interesting.
There are well over 100 commercial hops available now, with more being hybridized and released to growers constantly. There are hop varietals that have been grown and used in brewing since the 19th century, and brand new ones that hit the market each year. Hops are grown in many places around the world within the latitudinal band I mentioned earlier, including continental Europe and the UK, Japan, Australia, New Zealand, South Africa, across the northern United States, and many other places. Hops grown in different regions can showcase different aroma traits. Hops can have aromas that are grassy, herbal, earthy, or floral, or they can showcase a wide range of fruity aromas, from citrus to tropical fruits to berries. Name a fruit and there’s probably a hop that smells like it, often because they actually share one or more aromatic compounds in common. I’ve led tastings with beers full of tropical fruit aromas and flavors and had attendees who struggled to believe me that there wasn’t actually mango or pineapple in the beer; it was all from the hops.
Most of the commercial hops in the United States are grown in the Pacific Northwest states of Washington, Oregon, and Idaho, with the Yakima Valley of Washington looming particularly large (it’s common to hear the name "Yakima" used synecdochally to refer to the Pacific Northwest hops industry as a whole). That said, more and more small hop farms have been popping up around the country. There are even a few very small hop farms right here in my rural Ohio county. There’s a wild subspecies of Humulus lupulus that has evolved in New Mexico called neomexicanus, and hops can even be found growing wild in some parts of the country, often as feral remnants of domestic hop ventures from earlier in the 20th or even 19th centuries.
If our chocolate loving readers wants to experience the difference between hop aroma and hop bitterness, there are two chocolate bars I would recommend tasting side by side. Nostalgia’s Hop Aged bar was aged in a bed of Chinook hops, and the cacao butter in the bar soaked up the aroma of those aromatic flowers. It has a bold hoppy aroma—in this case orange and pine—but no bitterness, since the hops themselves—and their bitter acids—were not included in the bar. Somerville’s Beer Fermented bar, on the other hand, was made with cacao steeped in fermenting beer, right after the boil, and in addition to hop aroma packs a punch of hop bitterness as well.
Hops also play a role in the head retention of a beer and can sometimes play a role in controlling bacterial growth in some beers, but their most notable contributions are bitterness and aroma/flavor. It's pretty amazing this single flower species has such a profound influence on our favorite beers.