As your elementary school teacher used to insist, learning is fun—especially when you can learn through drinking. Accordingly, I’m a big fan of beers designed with educational intent. Brews like those in Mikkeller’s Single Hop Series or Terrapin’s lineup of Single Origin Coffee Stouts have expanded my knowledge of the ingredients used in beers by showcasing the flavors of individual hop or coffee strains.

A new duo of beers-for-learning, however, exposed me to a concept I had only briefly come across: the biotransformation of hop compounds by yeast. Here’s a decent explanation of what that means from an article on advanced dry-hopping techniques in the homebrewing magazine “Brew Your Own”:

“Biotransformations of hop compounds in beer can occur in two forms. The first is fairly straightforward, when one compound is transformed into another. An example of this would be the transformation of geraniol to ß-citronellol. The second biotransformation is the hydrolysis of the glycosides, which were introduced earlier. Certain yeast strains have shown the ability to transform non-aromatic glycosides into aromatic terpenoids. Shellhammer and Wolfe found that certain aromatic terpenoids increased their concentration over time in the presence of yeast. This may be just one reason many people find bottle conditioned or unfiltered beer to be superior to filtered beer.” tweet

This is Beer 301-level material, but it basically comes down to this: Yeast are not picky eaters; along with the malt sugars they ingest and convert into alcohol, carbon dioxide and aromatic esters and phenols, they’ll also absorb other compounds floating in the liquid wort, including those contributed by hops. Sometimes, when the yeast ingest hop oils, they’ll transform them into entirely different compounds, dramatically altering the hop profile in the finished beer. So, a beer packed full of hop oils during active yeast fermentation might taste completely different from the same beer hopped after the yeast have completed their work.

That’s the theory, anyway, and it was tested in a recent pair of double IPAs by Cloudwater Brew Co. in Manchester, England.

“I heard a couple of fascinating talks that brushed upon [hop compound biotransformation] at CBC this year in Philly, and came home excited to put a trial into our plan,” says Paul Jones, Cloudwater’s owner and founder.

That trial involved testing the concept of biotransformation using the next two batches of the brewery’s beloved DIPA. The two versions were brewed using the same wort, same yeast, same fermentation and same conditioning profile. The only difference: when the hops were added. In DIPA v4, the blend of Citra, Amarillo, Simcoe and Mosaic hops was added during fermentation to enable biotransformation to occur; in v5, the hops were added after fermentation to illustrate standard dry-hop aroma.

The differences between the two ales are apparent immediately. While v4 pours a pale tangerine hue—not perfectly clear, but you can certainly see through it—v5 is almost completely opaque and seems to have more retention in its sand-colored cap. It’s as stark a visual contrast as you’d get putting a bright West Coast-style IPA up against a turbid Northeast variety. The nose of v4 is catty, funky and herbal, but with nice tropical notes. Chives, mango, tangerine and a little wet grass swirl in a heady, perfumed blend atop juicy, pulpy orange and papaya. The aroma of v5 takes an alternate route: It’s lemonade-citrusy and so full of additional orange peel, orange blossom, honey and lime notes, it should probably be planted in a verdant California orchard. Smooth earthiness and a slight green pepper character accent the mix.

The beers’ flavors diverge as well. In v4, the hops come across as woody, almost mossy, with notes of overripe orange, mango notes, chopped onions, fresh grass blades and tangerine pulp injected throughout. More bright citrus shines in v5’s sip, with spikes of lime and garlic cloves. A finishing flash of mint seems messier than v4, and the bitterness is rougher, but its texture seems softer, with bitterness that doesn’t clear away quite as quickly.

If I had to choose: probably v4, even though I preferred v5’s aroma. DIPA v5 is intriguing but feels somewhat messy; v4 has a better close to the sip and seems a more put-together drink.

Feedback like the above is exactly what Cloudwater was looking for with this “public experiment,” Jones says.

“What we hoped to get out of brewing DIPA v4/v5, a public experiment with a beer that’s in high demand over here, is a learning experience for us as a team, and as much feedback from our customers as possible. We’ve been surprised by just how much difference there is between v4, dry hopped twice during fermentation, and v5, dry hopped after fermentation! Our intention is to use the feedback from our customers to help shape our processes across all our hoppy beers. I can’t say just now what our preferences are as I don’t want to influence folk who are yet to try the beers, but we conducted a private in-house tasting the night we’d bottled both, and have used the results of that tasting to make our most important DIPAs yet.”

Cloudwater will be taking those beers, DIPA v6 and v7, to Modern Times Beer’s Festival of Dankness on August 13. It’ll be the only non-U.S. brewery besides Mikkeller presenting its hopped-up wares.

See? Learning is fun.


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