I remember my first mixed-culture fermentation: I was so nervous about infecting my home brewery that I pitched a Lactobacillus culture into my Berliner weisse wort in the open-air environs of my deck, far from my preciously not-bacteria-laden equipment and fermentors.
The resulting beer (my Scared Sour Berliner Weisse) was successful, and I avoided creating a runaway Lacto infection in my brewhouse. That turned out to be an unjustified fear on my part. The biggest lesson I learned is that mixed cultures are nothing to be scared of, while they can be an outstanding way to expand your repertoire of flavor compounds, combinations, and profiles as a brewer.
A few quick hits before we go any further:
- First, don’t assume that when we say “mixed culture” we’re always talking about sour beer. That’s not necessarily the case—though the spectrum can vary from just a pleasant kiss of funk to bracing sourness, via gentle tartness.
- Second, a mixed-culture fermentation is not the same as spontaneous fermentation, where native cultures in the air or wood go to work on the beer. Creating a true “wild ale” entails considerations and risks that we won’t get into here. (For more on that, see Spontaneity: Prospecting for Bugs.)
- Last, and most important, is this: Don’t expect the bugs to do your work for you.
Too many brewers seem to think that the hard work is done the moment they pitch an exotic fermenting agent into their wort. Although a mixed-culture fermentation has the potential to create a more interesting beer than we may have brewed before, it’s still incumbent upon us to drive that beer to where we intend it to go. This requires attention to detail, and especially to the fermentation.
“Be as meticulous when crafting a mixed-fermentation beer as you would when brewing a beautifully crisp lager,” says Patrick Chavanelle, R&D brewer at Allagash in Portland, Maine. “Just because it’s a wild beer doesn’t mean that you can be careless.”
With that thought fresh in our minds, let’s get to work.
Know Your Bugs
Before starting any job, it’s a good idea to make sure we understand our tools. A “mixed fermentation” is any fermentation that uses more than one of several genera of microorganisms as a fermentation agent. For our purposes, that’s probably going to be Saccharomyces, Brettanomyces, Lactobacillus, or Pediococcus. That’s not remotely an exhaustive list, but those are the organisms we have the most history with in the context of brewing.
Saccharomyces is what we conventionally think of as “brewer’s yeast”—that’s our go-to workhorse in the brewhouse. Dozens of strains from a range of producers and sources give us a wide collection of flavor profiles, attenuation rates, and preferred temperature ranges. Sacc is a robust organism, grows up quickly, and will convert simple sugars into ethanol and CO2 with few off-flavors (when well-managed). It will (usually) form the base of our beer’s fermentation profile.
Brett, by comparison, is more of a slow-and-steady fermenter. It will consume a wider diet of sugars—and consume virtually all of them—but it will take its time. Left to its own devices, if pitched as the sole yeast for primary fermentation, Brett will produce a beer with a surprisingly clean profile given its funky reputation. Essentially, it produces that funk only when forced to work harder to consume sugars—for example, when Sacc or other yeast get there first. Since we’re talking mixed cultures here, it makes sense to expect and embrace those funky notes—which can vary widely and might be described as fruity, tropical, floral, vinous, barnyardy, sweaty, and more. There are many types of Brett, and they will produce different aromas depending on their environments.
Notably, there are two common misconceptions about Brettanomyces: One is that it will turn a beer sour, and the other is that it will not turn a beer sour. The truth is that it depends on you and your control of fermentation. Brett won’t produce lactic acid, but in the presence of oxygen it will produce undesirable levels of acetic acid. Avoiding oxygen will keep you from making vinegar. If there’s one thing to remember about Brett, it’s this: purge, purge, purge.
Moving away from the yeasts, we find two highly useful bacteria.
One is Lactobacillus, which has the virtue of producing a healthy amount of good, clean, brightly flavored lactic acid with minimal funky undertones. Lacto generally consumes simple sugars and works quickly, but … it’s touchy. Other yeasts and bugs tend to out-compete it, and it’s highly sensitive to hops, which limit its productivity. By the same token, however, you can also use a bit of hops to intentionally restrain that acidity.
Pediococcus is another lactic-acid producer. However, where Lacto is sensitive and simple, Pedio is like its brooding sibling: Expect some lactic acid, but also expect diacetyl, fruity notes (often like grape jelly), ropiness in texture, and the potential for a range of other funky flavors. The flavor of Pedio can be hard to predict, but it’s also hard to imitate—when you need it, you need it; it’s integral to the character of lambic, for example. Here’s a neat trick: Given time, Brett will break down the diacetyl and ropiness that Pedio can create.
Are there other bacteria and yeast out there? You bet, and more than we can discuss here. The core principle is this: Be conscious of the properties, propensities, and potential of what you’re adding. Keep it intentional.
Putting Mixed Cultures to Work
For starters, it’s a good idea to think about what a “simple” version of your mixed-culture beer would look like. Just as Allagash’s Chavanelle cautions us to brew deliberately with mixed cultures, we need to know where we’re starting.
“Knowing your base beer, and how it develops over time with a known culture, fleshes out the individual natures of the microbes in play,” says Sarah Resnick, blender and wood-program quality specialist at pFriem Family Brewers in Hood River, Oregon.
My prior experiences have validated this approach. If you don’t know what the beer does under simple conditions, it’s extremely difficult to predict accurately how it will behave under more complex conditions.
With the base-beer profile in mind, our next choice revolves around a classic dilemma: control of the details versus simplicity of method. If you want to maximize control, plan to pitch individual strains of microorganisms. This approach not only lets you select specific varieties of yeast and bacteria, it also allows you to “tune” your beer to a specific set of factors and aim at a smaller target for each. You can make environmental choices that empower healthy and productive fermentation, thus leading (one hopes) to a more accurate prediction of results. Timing and order of pitches, use (or not) of fermentation supports (oxygen, nutrients, etc.), temperature at different stages of fermentation, and more—those are yours to control. This puts the ball squarely in your court—but it might be a game you don’t want to play.
On the other hand, to maximize simplicity, you may choose to pitch a premixed set of cultures. These mixed cultures—available from many yeast vendors—are designed to emulate certain beers, regions, or styles in their mix of fermenting flora. One pitch, and you’re done. However, what you gain in simplicity you lose in control: As discussed in the previous section, different organisms have different parameters for optimum performance. Using a premixed culture will limit your options because all of your bugs are in the wort at the same moment. It’s a trade-off, but one that might be worth making, especially because it increases replicability (i.e., you can repeat the process with the same premade pitch).
This brings us to a fork in the procedural road: whether to pitch all your organisms at once (co-pitching) or to add them in sequence (staggered pitching). If you’re using the premixed culture, that’s decided: You’re co-pitching. But for those working with independent cultures, you may choose to give some strains a head start. Research on this shows variable effects—unsurprising, given the number of variables involved—but for a general method, I like to work from “fast-and-sensitive” to “slow-and-indiscriminate.” If you’re going to stagger (and you’re not going to measure pH or titratable acidity for timing), here’s what I recommend:
- Initial pitch: Lacto.
- At 48 to 72 hours: Sacc.
- Upon stabilization of gravity—or at 14 days, if not measuring—transfer to secondary vessel, then add Brett and/or Pedio.
This approach mostly keeps each strain from stepping on the others’ toes while reducing the need to take a strictly “diagnostic” approach.
So, we have the what and the when. Now let’s focus on the “how.” Below, we review some recipe and process advice to help you get the most out of your mixed-culture fermentations.
All of this guidance comes with a big caveat: Mixed-culture fermentations are much more variable in outcome than single-culture fermentations. We can guide, limit risk, and work with the end in mind, but these beers still require a certain willingness to embrace uncertainty. (Obviously, that’s easier for us as homebrewers.)
Again, brew deliberately. Pay as much (or more) attention to temperatures, time, and fermentation environment as you would in a simpler beer.
Focus on pitch rate. Under-pitching a monoculture Sacc beer still gets you that same base beer. However, when we’re using diverse organisms with different “work rates,” it helps to know when helping them along with a bigger pitch is warranted to get our basic profile.
Pay attention to fermentor materials. Glass rather than plastic will help limit oxygen in longer rests. Wood is another traditional option that can be inoculated.
The yeast or bacteria strain matters. It’s not just about which kinds of organisms you choose, but also which specific variety is at work. Just like Sacc, there are multiple strains of each bug. Do some research into the performance factors and flavor profile of specific strains (and/or go with a premixed culture) to ensure you’re working toward the flavors you want.
Consider late adjustments. Despite all that deliberation and care, you still might not get what you want. This is when post-fermentation doctoring can help. One option to consider: Brewing up different, simpler beers, and then blending them to taste.
Resnick at pFriem is one brewer who suggests trying this method, if you have space for it: “The availability of a variety of blending stock, including several strains of Brett and batches of beer guided by lab-produced cultures, has made us more agile,” she says. Controlling acidity is a challenge, she says, and blending is a good way to balance the final product.
Chavanelle at Allagash also suggests keeping an open mind when blending. “Keep your options open for blending in other mixed-ferm and non-wild beers, as both can be useful for adjustments to acidity and aroma,” he says. Another tip: Graduated cylinders are really handy for keeping track of your blending ratios.
To that expert advice, I’ll add this: Don’t be afraid to use food-grade lactic acid, added at packaging, to “cheat” your way to a brighter and bigger acidity. The final product will speak for itself.
Other adjustments: Resting on fruit or wood can add complexity, acidity, structure, and new flavors; adding Brett at packaging (hey, it’s good enough for Orval) can allow a touch of funk to evolve with time. (Just take care to avoid over-carbonation and bottle bombs.)
Blending and augmenting won’t fix every problem—it’s hard to blend out aggressively acetic or phenolic flavors, for example—but they’re in the toolkit. Be patient: Mixed-culture beers usually take at least three months and may take a year or more. Choose and use flavors deliberately and keep working toward your goal. The beer’s not done until you say it’s done.
Ending at the Beginning
Just as pitching multiple yeasts and bugs isn’t the sum total of what makes a great mixed-culture fermentation, mixing cultures is no cure-all. It isn’t a Band-Aid for dull or bad beer.
“Do you have a batch of beer that you’re considering adding wild yeast or bacteria to because it didn’t turn out as expected?” asks Chavanelle at Allagash. “You’ll likely have better luck moving on and starting from scratch as opposed to crossing your fingers hoping for the best. The best mixed-fermentation beers tend to be made with intention as opposed to by accident.”
Mixed-culture fermentations represent some of the best in brewing because they demand sizeable mastery of our art and our science. As brewing challenges go, this is about as good as they get. Do you need another reason to try?