Agrarian Brewing is on a hop farm outside Eugene, giving brewer and co-founder Nathan Tilley easy access to all the hops he wants. For a lot of brewers, that would be enough to keep busy. But since opening in 2013, at the peak of the Alpha Acid Era, Agrarian has never been content to stick with cones, making a steady stream of inspired seasonals.

Dryad was one of those one-offs—a dry-hopped sour ale with spruce tips that has a brilliant, yet smoothly restrained flavors.

"I think we struck on an amazing flavor combination with spruce tips and the bright lactic acid of our kettle souring process," says Tilley. "The beer is the result of some unique ingredients and creative techniques."

Kettle souring is a rapid process compared to traditional souring in barrels. They mash as they would be for any beer, then transfer the wort to the kettle and boil it for 15 minutes before cooling it to 115 degrees. Then, it's ready for souring.

"Our house Lactobacillus is pitched into the kettle and left overnight," Tilley says. "We check the pH in the morning, pull out a portion of the inoculated wort for a future kettle sour, then bring the kettle back up to a boil and continue the brewing process like normal.

The overnight souring process extends the brew day to two days, but the finishing time thereafter is the same as a standard ale. Dryad is made in all stainless-steel tanks. It sees no time in barrels and no wood contact at all—save for the addition of the aromatic tips of a spruce tree.

"Our kettle souring process allows us to measure and set the precise pH we are looking for," said Tilley. "For Dryad, the number is 3.44. Since the Lactobacillus is neutralized when boiled, we are fermenting a clean beer through the rest of the process, not a mixed culture, which can be a bit unpredictable."

Dryad is named for a Greek tree nymph. Its backbone is a combination of heavy of oats and the best organic malts Agrarian can find. The oats help retain the appropriate body in the final beer, important because Lactobacillus tends to strip dextrin during souring, leaving the finished beer thin.

"We ferment Dryad with a Kölsch-style yeast," Tilley says. "That yeast is inherently tolerant to lower pH.  We discovered that a lot of other yeast varieties fail to attenuate due to pH. Kölsch-style yeast gets us across the finish line."

Tilley's operation is one of several Oregon breweries that use their own farmland to grow the ingredients in their beer. And, indeed, Dryad is finished with spruce tips foraged from a tree that grows next to the brewery and then dry-hopped with Agrarian's own Crystal hops.