"Literally, for the last decade, all I've done is grow yeast," says Peetz, 32.
Not only does he presently provide yeast to breweries so that they can kick-start the fermentation of their beers, Peetz has previously worked on biomedical applications related to yeasts at Anschutz Medical Campus, and he worked for a biofuels company, GEVO, which uses yeast to convert sugar into alcohol in order to produce energy.
"I tell people that growing yeast is my only employable skill," he says wryly. But if there's a common thread in all of his activities involving those particular microorganisms, Peetz describes it as "being creative."
At Propagate's lab in Golden, Peetz isolates and then grows yeasts into colonies for his brewery customers, providing the yeast in liquid form to them. The yeasts are grown over two to three days within stainless steel fermentation tanks (which have been named after Star Wars characters like Boba Fett and R2-D2), proliferating within a sugary, malty nutrient media into which air is injected.
"It's pretty much the same process as making beer, except you dump the beer at the end and you keep the yeast," says Peetz. But, as opposed to within a brewery, Peetz's work is done within a HEPA filter tent, which ensures clean air and positive pressure in the work environment.
The specific yeast strain being grown might be one that Peetz has been "hoarding" in his cryogenic freezer. (So far, he has around 200 different strains.) Or a customer might ask him to isolate and grow a yeast from a favorite beer. "A number of the strains that we carry here have been isolated from bottles or cans of beer," he says. Some originated from abbey ales or biere de gardes from France or Belgium. Propagate's "Chico Ale Yeast" was isolated from ale brewed by Chico, California's Sierra Nevada Brewing Co. And its "Juicy IPA Yeast" is derived from beer made by the New England brewery The Alchemist. Another, "Brett Stave" contains a yeast isolated from "a Denver-based Brettanomyces brewery," he says.
Peetz explains that, legally, unless yeasts are genetically modified (which Propagate does not do), they aren't able to be patented. He says, "It's a double-edged sword: Anything that I find that's cool, anybody can take from me; and anything anybody else finds that's cool, I can take from them."
Propagate sells ale yeasts -- Saccharomyces cerevisiae. And lager yeasts -- Saccharomyces pastorianus. There are also at least ten types of Brettanomyces to make sour or Brett beers. Other categories within Peetz's yeast library include styles such as Saison/Farmhouse, English Ales, and German Ales. "I try to give people an opportunity to produce unique beers with yeast that you can't just pick [from] anywhere else," says Peetz.
That includes 14 different strains of Norwegian kveik yeast. Peetz says that brewing with kveik yeast just might be the next "big trend" in beer, since it offers several pluses to brewers: "[Kveik yeasts] ferment super fast -- like, within 48 hours, they've consumed all the sugars. They make very little off flavors in beer, so you can quickly ferment a beer, package it, get it out the door." And they're also viable when brewed at higher temperatures. Kveik can be used to make beer styles such as "lager, IPAs, New England IPAs, stout, farmhouse, or sahti."
Previously, Peetz had co-founded the company Inland Island Yeast Laboratories in 2014, before parting ways and launching Propagate in 2018. He says, "It's been nice to have complete control, this time, to set up a facility the way I think it should be done" -- which includes using stainless steel fermentation vessels.
Peetz continues, "The way we're growing yeast is totally different than any other lab" -- and although the details are proprietary, he does allow that it's "a methodology that we've come up that guarantees a higher yield of yeast with the same amount of raw materials."
After starting Propagate Lab in October 2018, the business had about five customers by the end of the year. A year later, it is selling it wares to around 100 different breweries within Colorado -- including Prost Brewing, Tivoli Brewing Company, Bent Barley Brewing Company, Peak View Brewing Company, Mountain Toad Brewing, Seedstock Brewery -- and a few in other states.
Peetz points out that brewers are especially concerned about any contaminants that could potentially ruin their batches of beer, especially in the wake of the legal matter involving White Labs and Left Hand Brewing Company. Propagate has recently put a Colorado State University graduate student to work on innovating the medium which the company uses to conduct its existing quality-control testing.
In his role as a self-described "Yeast Whisperer," Peetz often finds himself sharing advice with brewers on what malts and hops to use in order to complement Propagate's yeasts. He also directs the brewing program at Regis University in Denver. "It's a great opportunity to share what I've learned with other students," he says. "I really enjoy doing that.
Running a yeast business has its challenges, and the work itself doesn't garner all that much prestige within the brewing world. "It requires a very high skill set and a large capital investment," says Peetz. "And it's not sexy: If you love beer, for the most part, you want to make beer, not grow yeast."
Still, what does he find "sexy" about the job? "I enjoy working with yeast," he immediately replies.
Peetz knows you can't make beer without it. You can mix together malt and hop extracts, add grain alcohol, and then carbonate the liquid -- and you still won't have what people would recognize as beer. He points out that "yeast produces thousands of flavors -- esters, phenols, aldehydes, ketones, acids" that contribute to the "roundess, complexity, and flavor profile" within a brew.
"You've gotta have yeast in beer," says the Yeast Whisperer.
Challenges: "Continuing to pick up new customers," says Peetz. "How do you continue to tell people that you've got the best product, that you have all the cutting-edge equipment? And so, we're trying to do a better job of bringing people into the lab and showing them this is what we're doing, this is why we're the correct choice to use. It's continuing to try to change people's habits."
Opportunities: The yeast business is still not a crowded field. Peetz says, "Even though there's going to be 7,000 to 9,000 breweries by the end of the year in the United States, there's still only, like, six yeast producers. And so there is still a lot of opportunity -- especially out of state."
Needs: Propagate's 3,000-square-foot office/lab is maxed out. "Right now, we need more space," says Peetz. "We're at the point right now where we've got to move out of our current facility or hope that our neighbor moves out so we can expand."