Fruit Without Fear: Embracing Natural Inoculation

Borrowing a page from winemakers, some brewers are pitching freshly picked fruit instead of slurry, taking advantage of the natural yeast and bacteria on their skins—a process that requires a leap of faith and the best, ripest fruit you can find.

Jeff Alworth Mar 2, 2023 - 10 min read

Fruit Without Fear: Embracing Natural Inoculation Primary Image

Alesong believes that using locally harvested fruit, picked only at peak ripeness, produces better fermentations with naturally occuring yeasts. Photos: Courtesy Alesong

On a sunny fall morning 11 years ago, I drove from Milan to the tiny village of Marentino, just east of Turin. The nearer I got, the denser the vineyards, until my rented Renault was scooting along the ridges of rolling hills where the only interruption to the rows of Barbera grapes were hilltop castles. My destination was Valter Loverier’s LoverBeer, a small brewery known for its subtle wild ales.

That afternoon, Loverier introduced me to an under-explored process of wild inoculation: using clusters of those grapes growing just outside his brewery to inoculate wort. He believes he’s the first modern commercial brewer to pitch the skins of fruit as a medium of natural yeast, and I’ve found nothing to disprove the claim. He got the idea, no surprise, from nearby vintners who use the same microorganisms to ferment their wines. It didn’t take long for him to dose a batch of wort—and he even fermented it in a small foeder, so that the culture would remain to re-inoculate future batches.

A few years later, I learned that Oregon brewer Jason Kahler was doing the same thing to make his cherry and peach beers. His brewery, Solera, is in the hills below Mt. Hood amid vast acres of fruit—in his case, orchards of pear, apple, cherry, and peach. It remains an obscure practice (perhaps it only occurs to brewers sitting in the middle of flowering fields of fruit?).

But the practice is spreading, if slowly. Firestone Walker, literally founded on Adam Firestone’s winery, began a project focused on wine-grape inoculations. Farther north, in the lush Willamette Valley, famous for its pinot noir, Alesong was simultaneously pitching grapes as well. As Firestone’s project expanded, others jumped in with their own local grapes.


Although pitching yeast on the skins of fruit is a “spontaneous” process that few practice, it may be more accessible than using a coolship—if you’re willing to live dangerously.

Alesong believes that using locally harvested fruit, picked only at peak ripeness, produces better fermentations with naturally occuring yeasts. Photos: Courtesy Alesong

Pitching Fruit, Not Yeast

Alesong, near Eugene, Oregon, specializes in barrel-aged beers. The brewery makes many fruited beers, though most of them follow their more typical process of starting with yeast and bacteria inoculations. Even in that process, cofounder Brian Coombs says the effect of the wild stuff is obvious. When they add fruit to fermented beer, he says, “that kicks off another fermentation that is very different depending on the fruit and that is very native.”

In their wild inoculations via fruit, Alesong starts with a high-protein wort and a base beer that is “pretty boring, just an empty canvas.” They design it to survive the ravages of all those fermentations, not to taste great from the fermentor. Alesong doesn’t do much to prepare the fruit—in fact, the less they handle it, the better. In past years they’ve done a light stomp just to break open the grapes. Coombs likes whole-cluster grapes because the stems and skins add tannins and depth.

Alesong doesn’t let the beer sit on the fruit the whole time it’s aging, as some brewers do—such as Kahler at Solera. Kahler alternates between a cherry- and peach-inoculated batch and releases it the following year, never having removed the fruit. “At the end of the year, I pull [the cherries] out and there’s nothing left but stones,” he says.


At Alesong, however, Coombs lets the grapes do their work, pulling them out when the beer has again fermented to dryness.

In 2017, Firestone Walker began their Terroir Project of grape-inoculated beers. After a couple of years, they started using a technique developed by winemakers called “carbonic maceration.” Jim Crooks led the project as master blender at their Barrelworks site in Buellton, California, working alongside Molly Reed. He left in June of this year, and Reed has stepped in to replace him. She outlines this process: “We get the grapes, and we have them intact, and as gentle as we can be, we put them in a bin and purge it with CO2. We leave it for several weeks, and then the initial fermentation takes place intercellularly.” Afterward, they crush the grapes and pitch juice into fresh wort. “It produces beers that are fruitier and less acidic—these beers are some of the least acidic we produce at Barrelworks.”

Alesong and other breweries also began to participate in the Terroir Project, which calls for 49 percent of the fermentables to come from grapes—though when Alesong started doing this before joining the project, they were pitching 35 to 40 percent. However, Coombs says he doesn’t think the concentration matters as much as the variety, vintage, and farm.

“Pinot noir from one vineyard can be drastically different based on farming techniques,” he says. “So I think that the actual fruit that you’re taking is much more determinate on what your flavor profile and … your tannin structure [are] going to be than the difference between 40 or 49 percent concentrations.”


The Key Is Ripeness

Because it enters the national food chain and must last days or weeks, fruit is rarely picked fresh. I was struck years ago when Kahler, at Solera, mentioned he had to forge personal relationships with local farmers so that they’d leave the fruit on the trees until it was at the peak of ripeness. For a healthy biome living on the skins of the fruit, that’s critical. The longer the fruit hangs on the branch and the sweeter it gets, the more natural yeasts and bacteria will gather on the surface.

This is something Coombs emphasizes over and over. While he acknowledges that breweries have many different approaches to working with fruit, he doesn’t equivocate on the importance of ripeness. “I’m totally confident of that,” he says. “That’s what the yeast and bacteria like. That’s when the birds start to eat it, and that’s when the insects come out and all these things. Nature is showing us these fruits are in their optimum time right when they’re ripe. If it’s picked super-early and there’s not a ton of sugar in the fruit, there’s just no reason for the yeast and bacteria to be there.”

Both Alesong and Solera emphasize that organic fruit is much better; you don’t want pesticides in the beer, but you also don’t want it retarding healthy yeast growth. Yet when you’re dealing with live cultures on skins, you might want to take additional steps to limit handling. “My theory is that there’s a yeast cell-count issue,” Coombs says, contrasting a batch of shipped fruit to grapes that came from their neighbor to the west, King Estate. The fermentation with the shipped fruit was slower and less healthy, “because they’re picked, and then they’re refrigerated, and then they’re shipped to us, as opposed to just getting picked that morning and put into beer that afternoon.”

Whether using fruit to inoculate beer or as an ingredient, Coombs encourages brewers to think like winemakers.


“Your quality of fruit matters so much,” he says. “It comes through in the flavor, and it comes through in the fermentation. Your tub of raspberry purée that’s [from] a conglomerate of different fruit producers is going to be different [from when] you go to a single producer and select what fruit you get. We do that with hops. We understand that with hops.”

It’s Still Spontaneous

The decision to inoculate with fruit is largely a philosophical one. It means sacrificing control over how the beer will taste. The fruit itself will dictate much of the flavor, and previous decisions made by the grower are out of the brewer’s control. Yet rolling the dice on the bugs that live on the skins is far more radical.

“If you’re buying [yeast] from a lab, you’re really trying to control the process, you’re trying to drive the end result,” Kahler told me years ago. “It’s kind of magical in my head; you just need to trust your process and let it play out.”

There’s a reason that Firestone Walker dubbed their grape-inoculated beer the Terroir Project. They could have chosen to compose wine-beer hybrids with lab yeasts, letting consumers taste the differences in grape varietals—but that’s only part of the terroir. The wild yeast and bacteria are a big part of the flavor of a place. Indeed, the differences between the microorganisms in Santa Barbara County and the Willamette Valley may be more profound than the flavors in grapes from those places.

“I don’t worry too much about spontaneous fermentation,” Kahler says. “That’s something that you have to get over, your fear, if you’re going to try these beers. You can’t lose sleep over something like this.”