Class captures wild yeasts for brewing, learning

AMES — Yeasts are everywhere. These single-cell organisms, found widely on animals, plants and ripened fruit, are nature's fermenting agents.

They are also the focus of a class, Biochemistry of Beer Laboratory, offered through Iowa State University’s College of Agriculture and Life Sciences.

Scott Nelson, a professor in the Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, teaches the course. The recent recipient of the Regents Faculty Excellence Award, known best for his research into the keystone elements of DNA repair, is also an engaging instructor with a passion for beer and brewing.

His popular course got a boost when Nelson received a small grant for it through the CALS Innovation and Entrepreneurship Faculty Fellows Program in 2024. The funds went for brewing kegs and ingredients, like barley and hops. He said the support was a “nice bit of recognition for a course that’s fun, but also a fair bit of work.”

Most of the students who take it aren’t science majors. “Maybe they looked through a microscope in high school, but they never really had a wet lab experience or were given a project they were responsible for,” Nelson said.

“It turns out that yeast can be a good gateway to learn about microbiology, biochemistry and the scientific method. Though it can be a slow and sometimes frustrating process, by the end of the year, students usually succeed in isolating a yeast, and they get to make a beer with it.”

The first step is collecting yeasts. Students learn about their samples in the classroom and Nelson’s laboratory. By semester’s end, they take their favored yeast into a food-safe kitchen where it is mixed into a mash. The liquid is siphoned off to age for a month or more. Tasting is not part of the course, but students who are old enough have a chance to sample their finished brews.

Yeast from a lion’s mane

Wild yeasts have advantages. They tend to have a more novel range of aromas and flavors, according to Nelson. However, they have some challenges when it comes to commercializing. Domesticated yeasts used for brewing can survive higher alcohol levels than most wild yeasts that usually produce just enough to eliminate bacterial competition.

Several local breweries became interested in Nelson’s course and have hosted student tours after he co-led a workshop on yeast cultivation and management through the Iowa State Center for Industrial Research and Service.

In one case, the students worked with No Coast Brewery in Oskaloosa and Blank Park Zoo in Des Moines to capture a yeast from a lion’s mane (collected by a zoo veterinarian) with the idea of turning it into a featured beverage for Zoo Brew events. Students used it to create a beer that Nelson describes as “really good — a cross between a Belgian wit and a German Hefeweizen. The beer hasn’t been commercialized yet, but that could still happen,” he said.

Isolating a new yeast species

Most of the yeast collection for Nelson’s course takes place in tamer settings than a lion’s den, but the results can still be exciting. In 2021, Everett Hargrove, now a senior in economics and statistics, took the brewing course to earn some required science credits. He collected samples of flower petals and a ripe walnut from his backyard.

“It was really interesting: Both the lectures that included the history of brewing and the hands-on experience in the lab," he said.

“There are a lot of steps. From doing the diagnostics of the yeasts, like did we even collect any?” Hargrove said. “We ruled them out if they smelled bad or were likely to ferment into something toxic. Then, we had to figure out if they would be alcohol-tolerant. If so, did they have potential to taste good?”

They cultured the yeasts and tested their DNA. One of Hargrove’s didn’t match anything that had yet been identified. Thought to be a new — or hybrid — species, it was also able to exist in an environment of 4-5% alcohol.

“It actually had good brewing attributes, too, so that made it even better,” he said.

“I’m still making beer from it at home,” Nelson said. “We’re writing a paper about it. If it’s published, Everett’s name will be there as a co-author.”

A passion for brewing

Nelson began his beer-making hobby when a graduate school roommate was gifted with a beer-making kit. Almost 30 years later, he’s still learning and refining his skills. He has long been active in the Ames Brewers League and enjoys sharing his hobby with students as an engaging introduction to science.

“Who knows,” he said. “When I retire, I might start my own little nano-brewery based on wild yeasts. You never know what you’re going to find out there.”