There are many ways to develop and maintain mixed cultures of yeast and bacteria. For the purposes of this discussion, we’ll focus on three types of cultures as we define them. This terminology isn’t intended to be definitive, but it’s useful to explain what we mean when we use shorthand terms.
In wine- and cider-making, a native fermentation is one that occurs without pitching a culture. In any fermentation, it’s possible for fermenters to come from ambient sources or contamination from equipment, such as barrels, tanks, or presses. Generally, a native fermentation is believed to occur due to yeast and other cultures that reside on the skin of the fruit. It is common for native grape cultures to contain Oenococcus or other malolactic bacteria, and I’ve had success using native grape cultures that contained Brettanomyces. Native cultures also can be gathered from flowers, but in my experience, this is a more esoteric pursuit. My suggestion for those who pursue it is to use very low-gravity wort with proper acidification and no hopping.
While many lab scientists will refer to “wild” Saccharomyces strains, our use of the term in a brewing context is solely to describe cultures taken from a coolship or similar ambient inoculation. While most coolship inoculations take place in existing breweries where the culture inside the building is largely what’s captured, it is possible to capture and propagate fermenters from the air in places where there is no history of fermentation.
Many of the cultures we use at Floodland are—at least in part—appropriated. Yeast wants to grow. In all bottle-conditioned beers you will find yeast, and in many you will find several fermenters that can be given new life in your beers.
Whether you’re new to mixed-culture brewing or not, appropriating yeast from other bottles is one of the best ways to create a new culture. For our beers, I prefer a Sacch-dominant blend. I created the original Floodland saison culture from dregs from Au Baron’s wonderful Cuvée de Jonquilles along with dregs from Blaugies Saison d’Epeautre and Thiriez Extra. All three are worth seeking out just to drink, and I sought them out for nostalgic purposes, since they were all pivotal in my appreciation of saison.
More on Native & Wild Cultures
When starting a native fermentation or capturing a wild fermentation, it’s useful to take into account that fermenters from any fermentations in the area are likely to drift in on the wind. If you live a half-mile from a lager brewery and set out a homebrew coolship overnight, don’t be surprised if you end up with a culture that ferments malt sugars, flocculates, and leaves you with a bright beer after a relatively short time. (Congratulations, you just got free lager yeast.)
Take special care with attenuation when capturing and brewing with a wild culture. Many yeast strains not developed in a brewing environment will not ferment malt sugars. These strains can happily coexist with more attenuative strains, but be careful when packaging beers that contain a variety of fermenters; one part pale ale and one part beer with Brett can lead to bottle bombs, which is very dangerous.
The Care & Feeding of Your Mixed Culture
When setting out to develop your own culture, it’s useful to have practice with yeast starters. Professional brewers have learned through practice that re-pitched yeast is happy yeast and that yeast often doesn’t hit its stride until a few generations in. These practices can and should be developed for ale and lager as well as mixed-culture brewing.
Propagate the yeast as you would any yeast starter. Don’t simply pitch bottle dregs into a carboy and expect them to ferment happily. Your culture is not a Tamagotchi, but you can think of it as one—it needs nutrients and attention to grow before it can go out into the world. I suggest an 8°P (1.032) wort for capturing bottle dregs, and you’ll be best served using a small volume: 7–17 fl oz (200–500 ml) is a good starting point. If you want to try capturing native cultures, use a 4°P (1.016) wort.
If you’re new to making yeast starters, I suggest heading down to your local homebrew shop and picking up some dry or liquid malt extract. A small Erlenmeyer flask or mason jar retrofitted with an airlock (or even a piece of foil) can work as a vessel. (Editor’s note: See “How to Make a Yeast Starter,” beerandbrewing.com, for detailed instructions.)
When appropriating yeast from bottle-conditioned dregs, you’ll find that the fresher the bottle, the more viable the yeast used to condition it is likely to be. American-brewed saisons may be a better option if it’s hard to find Belgian or French bottles where you live. In older bottles, you’re more likely to grow more Brett or bacteria than Sacch.
The balance of Brett to Sacch to bacteria in your culture will significantly affect the finished qualities of your beer. There are many tools at your disposal to modify that balance, and in time you’re likely to find that you’ll want every trick at your disposal to inhibit acidification. Here are a few things to keep in mind:
- Harvest times: Harvesting your mixed culture soon after primary fermentation (for example, two to four weeks after pitching) by moving your beer to a secondary vessel will yield a more Sacch-heavy slurry.
- Hops: Hops inhibit most bacteria, and you’ll find that their bacteriostatic properties are a valuable tool in shaping your culture and the beers it makes.
- Storage temperature: Many bacteria strains don’t deal as well with refrigeration as yeast strains do, so chilling your culture after harvesting can be a way to help knock down those populations. Conversely, if you want to encourage your bacteria, keep the culture cool but not cold between uses. (You will see declines in yeast viability when doing this.)
- Pitch time and rate: If your culture becomes too Brett-dominant, a simple tool is to re-pitch a smaller portion along with fresh Sacch.
Acetic acid: Brett, when in the presence of alcohol and oxygen, will produce acetic acid. It can be pleasant in small quantities, and it’s a signature trait of aged lambic, but many people find it off-putting. At high levels, acetic acid will make your beer more useful as vinegar than for drinking.
Bottle-conditioning: Mixed-culture beers benefit from bottle-conditioning. Bacteria and Brett can both produce tetrahydropyridine (THP), a retronasal flavor that often comes at the end of the swallow and has both a palate sensation and a flavor/aromatic profile similar to toasted corn, grain husk, or cereal. Given enough time, Brett will break it down in the bottle. A force-carbonated keg or bottle is less likely to be clear of THP once it forms.
Patience and safety: Brett and many other yeast strains found in wild/native cultures can be hyper-attenuative, which means you need to be confident your beer is at a terminal gravity when you package it to avoid dangerous situations such as bottle bombs.