You can see some of the differences between an old growth forest and one that's been logged.
On a hike through an old growth forest near Portland, Matt Wagoner of the Forest Park Conservancy points out some of the most obvious ones: Older, taller, coniferous trees, dead trees both standing and fallen, and a wide variety of plants and animals living inside of and on top of that dead wood.
"One of the things that really defines old growth forests is biodiversity," Wagoner says.
Wagoner and brewer Dan Hynes of Thunder Island Brewing in Cascade Locks, Oregon, want to know if that diversity carries over into the wild yeast that you can't see. Yeast is a fungus, as well as a fundamental building block of beer. To test the diversity of wild yeast in an old growth forest, they decided to try tasting it.
They collected wild yeast from sites within an old growth and a logged forest and used it to brew several different beers. Ultimately, Wagoner says, they're curious: "What if you can really taste the differences between a yeast that's gathered in an old growth forest as opposed to a second growth forest?"
Their experiment is part of a program called Beers Made By Walking that's leading brewers on hikes across the Northwest to look for local beer ingredients.
When Eric Steen created the program, he says, the idea was to tap people's interest in beer to connect them with the local environment. The result has been beers made with native plants such as salmonberry, stinging nettle, wild ginger, vanilla leaf and the tips of spruce trees. Using yeast from a local forest takes the idea one step further.
"We've been joking – but only half joking – about the possibility of making beer not only with ingredients inspired by a trail but also in collaboration with the trail," Steen says. "This adds another layer to learning about nature."
To harvest wild yeast from the forest, the brewers used buckets of unfermented beer –- basically sugar water –- known as wort.
They set the buckets at noteworthy locations in the forest: Alongside a decomposing nurse log teeming with moss and sprouting plants, next to a giant snag full of holes where wildlife have made their homes, under a cedar tree with a strip of bark removed in the traditional Native American style, and under a 500-year-old Douglas fir tree. The fifth location was at a site next to the old growth forest, where it adjoined a forest that was logged about two decades ago.
They left the buckets in the forest after a snow storm in February. Then, Hynes brought the yeast back to his brewery and cultivated it for three weeks.
The green, puckering taste of the resulting beer, he says, tells him that the yeast he collected in the forest is a less common type of wild yeast. He suspects that a lot of the more common yeast was less prevalent in the forest because of the cold February temperatures.
Yeast is in the air all around us, he says. But brewers normally reuse the same types of yeast that originally produced traditional lagers and ales.
"Our normal yeast is more like a cow," he says. "It's been bred over periods of time, and it has its different personality traits. So, you can kind of know about it."
He wants to know what kind of yeast is in the air now and see what kind of beer it can make.
"It's your antelope, your elk, your moose – that's what we're hunting down," he says.
Over Memorial Day weekend, Wagoner, Hynes and Steen led hike of about a dozen people through the stands of trees where they harvested the yeast. They stopped at each of the locations where they'd harvested wild yeast and poured samples of the resulting beers so hikers could see the locations and compare the flavors of the resulting beer.
Beer writer Lucy Burningham was one of the beer connoisseurs on the hike. She says the beers made from the forest yeast are sour, for sure. And she tasted elements of other sour beers she's had before.
"But I think what's unique is the place that we're standing and the sounds I'm hearing as I'm tasting these beers," she says. "This is a unique experience for me."
She says the flavors of the forest aren't what she was expecting. It's not like she could literally taste cedar in the beer that was made from yeast collected under the cedar tree.
"I think it's definitely changed the way I'm thinking about the forest," she says. "There's all these invisible things that are part of the forest that have now shown up in the beer."
Steen says that's the reaction he was hoping for. He says it's not that the resulting beer is that much better than other beers. It's how the beer allows people to experience the forest.
"I like the idea of thinking of these beers potentially as artwork – as drinkable sculptures, as drinkable portraits," he says. "It's another way to interpret the landscape, to interpret the trail."
Steen has several more brew-based hikes planned for Forest Park this summer. The resulting beers -– including the old growth forest beer and a logged forest beer made by Hynes –- will be on tap at a tasting event in October.