Where the Hops Are Preserved

Earlier this year, the world learned of a new hop: Monocacy. The story started with a farmer curious about apparently wild hops growing on his farm. After a decade, word of the hops filtered to researchers at the University of Maryland, who sent it to USDA’s National Clonal Germplasm Repository in Oregon for testing. John Holl posted a great piece about it in All About Beer. When the results came back, they learned that “the hop was completely genetically unique,” John wrote.

I didn’t pursue it much further because he lays everything out beautifully. Well, except, not everything. The passage about sending it off for “testing” leaves a lot to the imagination. Who tested it? How are hops tested? I was especially interested in its genome. We’ve learned a lot about the distinct sub-species of Neomexicanus hops that have become grist for a number of new commercial cultivars. Was Monocacy related to them? Was it a wholly new, different line of native North American hop?

Those questions led me to that Germplasm Repository mentioned in John’s article, in Corvallis, and to the office of Dr. Nahla Bassil. What I discovered was incredibly fascinating, and went far beyond the scope of a single wild Maryland hop. It turns out that the Repository is ground zero for information about hops, and not just new ones.

A Living Museum

Everyone has heard of a seed bank, a kind of external hard drive that backs up our rich genetic diversity. They’re great resources, and may become incredibly important in the decades of changing climate to come. Yet they’re incomplete. Not every plant reproduces reliably by seed. Plant the seed from a Granny Smith apple, for example, and you won’t get a Granny Smith apple tree. They’re like humans this way—we don’t replicate perfect little copies of ourselves, either. Plants of this type need to be cloned. Hops are like apple trees, and you reproduce a variety by planting a rhizome, which looks like a root but is actually a subterranean stem.

Lots of plants are heterozygous—they produce offspring that differs from the parent—so preserving their seeds is not much use. Instead, ARS maintains sites across the country that keep a living inventory of plants rather than seeds—“clonal repositories.” The sites maintain plants that grow in the regions, so for example, the Hawaiian site preserves pineapple, breadfruit, papaya, rambutan, guava, and cacao. Iowa, on the other hand, specializes in things like corn, millet, sunflower, and flax. The Corvallis inventory includes pears, hazelnuts, mint, berries—and hops.

Corvallis maintains over three hundred separate varieties of hops, many that we know, some wild varieties, some obscure varieties, and some ornamental varieties. They even maintain a greenhouse where hops have been infected with various common viruses. Beyond taking care of these plants, Dr. Bassil and her team do research—including looking at markers on hops to determine what kind they are. And that’s why researchers in Maryland sent the Monocacy plant to her.

Fingerprinting a Hop

So what happened when they sent Dr. Bassil the Maryland hop? She invited me down to Corvallis to explain the process. The Agricultural Research Service is the in-house research agency for the U.S. Department of Agriculture, and it turns out Dr. Bassil doesn’t work alone there. When I arrived at the modest building where her office is located, I was surprised to find a whole team ready to greet me. This was not like the brewery tours I’ve gotten used to, where things are a little more free-form. The team offered me a tour and presentation, and when we finished, Dr. Bassil looked at her watch and said, “We’re only three minutes over time.” Absolutely not like a brewery visit.

The process starts with a piece of the plant. “You want the tissue of the mother plant, not the gamete [like a seed]” she began. “Young leaf tissue has less secondary metabolites, and the DNA is cleaner.” For some reason, I assumed they’d actually use the hop itself—I suppose because that’s what scientists test for things like oil content. Nope, they take a small bit of leaf and grind it up until it becomes powdery. They use a “buffer”—a chemical compound—to separate the DNA from the plant, and then unzip the paired DNA strands under high temperature with an enzyme and more chemicals, and “amplify” certain sections of the DNA sequence. As she continued, I’ll confess the science started to float above me in the way trigonometry did in high school.

The upshot in this process is sampling just a part of the DNA, rather than looking at every gene. Those sections are known as “markers,” and that’s how they distinguish among hop plants. They select regions that will help them tell the hops apart. “The markers are regions in the chromosomes that are very variable between different individuals,” she told me. Some plants are more alike, some different, and require fewer or more regions.

“On hop DNA, nine different regions are amplified. Sometimes plants have the same fingerprint in one region, so you want more regions so you can distinguish the different cultivars. You’re targeting a specific region that is highly variable between individuals. With humans we used to start with 13 different regions, and they’ve added more. Depending on how variable the crop or species is, then you may need more. If it’s not very variable, you need more. We use 14 markers in hazelnuts.”

In the end, they produce an electropherogram, or visual graph of the different markers, and that distinguishes them from other hops, and also allows them to group the specimen with similar hops, like cousins in a family. This is Cascade:

Fingerprinting has its limitations. I wanted to get back to that question about whether Monocacy was a wild hop. According to the results of the fingerprinting, it clustered with other wild North American hops. That’s a particular type, distinct from Neomexicanus. So Monocacy is a wild hop?, I asked. “We don’t know,” Dr. Bassil told me. In that precise way scientists think, she was careful to characterize what they did know.

“It could be a cross with a cultivated hop. But when we compared everything in our database, which is 600-some individuals, the first thing we can say is that it had a unique fingerprint. It wasn’t the same as anything else in this database. And second thing is that it grouped with the wild North American hops, indicating that there is wild North American hop in it.”

The Collection

As they approach the repository in Corvallis, sharp-eyed visitors might notice an orchard before they reach the parking lot. Those are their pear specimens. You won’t see trellises for hops, though—they keep those inside greenhouses (or, as I learned, technically “screenhouses”). After visiting the lab and learning about fingerprinting, Dr. Lauri Reinhold and Gabriel Flores took me on a tour to see them. The facility is going through a big renovation, but we found their cozy homes filled with pots and bines at different stages climbing out of them. This is the only home the hops will know. They keep them in a screenhouse to protect them from pests, disease, and cross-fertilization.

Beyond the work of fingerprinting, Dr Bassil’s laboratory works on other projects. One of the most valuable may be work done by Dr. Shaun Clare, who has developed a new technique for distinguishing between male and female plants. It’s curious that they haven’t found a specific gene for determining sex—but they have found associated genes that are correct 95% of the time. “The way Dr. Clare developed it is by associating a variation with the trait,” Dr. Bassil said. “That association didn’t get us to the gene itself, it got us very close to it. That’s how markers are, you find an association. That’s what Dr. Clare did: he developed a tool to detect that difference between the male and female.” This will be very valuable for breeders, who only want to grow female plants for commercial production (males are too seedy). It should save them a lot of time weeding the males out of their populations. A paper on the technique was just submitted.

Gabriel assists Dr. Reinhold in managing the hop plants. “We’re simply preserving genetics,” he said. “If we have things flowering and coning and breeding with each other, then we’ll lose the integrity of our collection. It’s difficult. All these hops will grow laterals and they want to climb onto their neighbors, so it gets a little dicey. They can grow six inches a day—sometimes more. You’ll leave on Friday and you’ll come back on Monday and everything’s up here in the rafters. They take quite a bit of work.”

Since these plants aren’t grown to provide tasty hops for our IPAs, the folks tending them have a different relationship to their charges than a brewer might. Grouped roughly by region, we could see some of the plants already beginning their spring climb, while others only had tiny shoots emerging (I visited in March). They showed me a plant with blue leaves. We looked at other plants that had unusually-shaped leaves with a single main lobe, unlike the characteristic three- or five-lobed leaves I’d seen in the fields. They talked about which plants were aggressive, and which were more demure. They even described their behavior, as if they had personalities.

At one point, Gabriel took me to see their latest addition, that Monocacy plant. They continue to add to the collection, even going on expeditions for wild hops where they get reports of potential varieties growing wild. One group they don’t maintain, however, are proprietary hops. Perhaps once those fall into the public domain they’ll make their way here. For now, it’s all public commercial and wild varieties.

After the main collection, we looked at the virus- and viroid-infected plants. They, too, may hold important secrets. Which plants resist viruses and viroids better? Which viruses and viroids are actually not harmful for the hop? Are any viruses or viroids beneficial in provoking the hop to create interesting flavors? All of these are interesting questions, and over time we may learn the answers. Everything I saw, from the fingerprinting to the research to the collection and the virus- and viroid-infected plants were all resources for scientists. And all the research they conduct will become public and go out to other scientists. Of course, this is just one type of plant from the scores that ARS maintains in these sites.

Before I left, we climbed into a pick-up and drove through the pear orchard. It was a tempestuous day, pouring when I arrived, but momentarily sunny as we drove. I asked if they maintained any perry pears (the type used by cidermakers), and they did, and that set us off on an entirely different conversation. In fact, they have around 2,300 different types. We didn’t visit the berries—though I adore strawberries and am very interested in their collection—or the mint or the hazelnuts. Yet each one contains dazzling biodiversity. Multiply that by the sites around the country and all the lines they maintain, and it’s an impressive collection.

Until Monocacy hops popped up on my radar, I had no idea such a network existed. If you go over to the website (which honestly is a bit of a mess), you can see if there’s a repository in your area. I’m not sure how available the sites are for general tours, but the work they do is interesting, and you should have a look. Meanwhile, the next time you hear of a new hop discovery, now you’ll know where they went to find out more.