Spontaneous Fermentations: Tips from the Pros
Wild beers can be fermented a couple of ways —from pitching cultured yeast/bacteria or leaving the wort exposed and allowing it to ferment spontaneously, as Belgian lambic brewers do. While riskier, spontaneous fermentations result in some of the most unique and complex flavors known to brewers. In this issue, two pro brewers share advice for homebrewers to have successful spontaneous ferments at home.
Van Carney, Co-Owner/Brewer at Pen Druid in Sperryville, Virginia
We have two programs for fermenting beer at Pen Druid: Spontaneous and pitched. All our clean beer is fermented with an indigenous wild yeast that we captured from a flower that was underneath an apple tree beside the brewery. We do not isolate or keep this yeast banked. We merely pitch it batch to batch to keep it going, using the age-old palate technique to make sure it’s good to pitch. With our spontaneous ferments we rely on the coolship and the resident yeasts and bacteria deep in the wood of the fresh steam cleaned red wine barrels that we use to ferment our spontaneous beers.
The difference in these two beers is noticeable. Spontaneous beer made in the traditional method has a long, lateral palate and a finish that goes forever! It typically has a lactic acid presence, of varying degrees, and no acetic acid. Our wild clean beers are devoid of lactic acid-producing bacteria, so they are crisp and clean.
For our spontaneous beers we use traditional spontaneous methods that Belgian lambic producers use in order to make a poor wort that ferments very slowly, forms a pellicle to protect against oxidation, and allows microbes to do the work that can take years to complete. Spontaneous ferments allow for this and therefore can produce the most complex beer, which is what we want to drink.
We brew these beers in the traditional method, so a ratio of 60/40 Pilsner-to-raw wheat, a traditional turbid mash schedule, and aged hops. Our coolshipping season runs from October–April and fermentation is consistent throughout the season for us. After racking to barrels we don’t touch them at all for 18 months. Then we fruit some of the last brewing season’s barrels, and we do our 1-, 2-, and 3-year-old spontaneous blend. The youngest spontaneous beers we package is about a year old.
We only taste when we are ready to package, and at that point you’ll know what you’ve got. We end up dumping about 25–40% of any given year’s barrels, which is one of the risks you face with spontaneous fermentations. We dump barrels when they are oxidized (cardboard), have any level of ascetic acid (vinegar), ethyl acetate (acetone), butyric acid (puke), isovaleric acid (sock cheese) or in other words the beer is weird or gross. Also, too much oxygen can cause production of aldehydes, which can create bruised fruit flavors that can work in aged barleywines, but typically don’t work in our spontaneous ferments. The key things to prevent oxidation are proper pellicle formation and not touching the barrels at all. Other issues such as ropiness, diacetyl, acetaldehyde, Tetrahydropyridine (THP) and some Dimethyl Sulfide (DMS) and S-Methyl Methionine (SMM) compounds can work themselves out with further aging and patience.
When a beer is ready for the bottle is more a matter of experience and less about specific criteria. Why things go wrong in a barrel is the stuff of a PhD thesis, but using your palate to judge what you like and don’t like is the most important thing and that’s the fun part of it! Take pleasure in sampling barrels, making blends, bottling, messing up horribly, sometimes succeeding, and knowing that success is positivity in the face of failure!
James Howat, Founder/Brewer at Black Project Spontaneous & Wild Ales, Denver Colorado
To me, the biggest appeal of spontaneous fermentation is the diversity of microbes. One can, in theory, make sour beer using only one strain of lactic acid bacteria and one strain of yeast from a lab, but I believe the most interesting, complex, inspiring beers are those made from a wide diversity of microbes — hundreds of species potentially — that come from the local environment instead of a lab. The capturing of a true spontaneous ecosystem means that unlike a beer made with lab microbes, a spontaneously fermented beer cannot be made anywhere else. The complexity, depth of flavor, and terroir of a well-executed spontaneously fermented beer cannot be replicated with other methods.
At Black Project, all of our beer is inoculated via a 320-gallon (1,200-L) copper coolship. We do two different types of spontaneous beers. One is a traditional lambic-style brew, inoculation, fermentation, and aging. More on the procedures we adhere to on that can be found on MethodeTraditionnelle.org. However, we also make some of our base in what we call a spontaneous solera. We have large vessels that were started years ago using mature spontaneously fermented barrels. Since then they have never been completely empty. We remove, say, 25% of the volume to fruit or package, and then replace it with fresh wort from the coolship. It doesn’t create quite the same depth as the traditional style of spontaneous fermentation, but it creates a slightly more consistent product in both character and production time.
We prefer the wintertime, when it is cold at night, for our traditional spontaneous beers. I think the differences between seasons are mostly based on cooling rate vs. what microbes are present in the air. A slow cooling rate means that, for example, enteric bacteria (which are indeed an important early part of the process all year) can get out of hand and ruin the beer before other genera can catch up.
I don’t recommend tasting traditional spontaneous beer for at least a month or two. You want to make sure the pH has dropped and alcohol is present, otherwise there is a theoretical risk of botulinum poisoning. If you do taste during aging, know that the beer is going to go through cycles early on where it will taste better, then worse, then even better still. You have to experiment and know what your native flora does.
Ultimately spontaneous beers are about blending and I think the biggest struggle homebrewers have is not thinking like a blendery. You need many batches of the same beer in order to craft something really good. It is exceptionally rare for us to have one single barrel (out of 150+) that I would sell on its own. I often see homebrewers make one 5-gallon (19-L) spontaneous batch and get disappointed and surprised that it isn’t exactly how they thought it would be . . . but that’s the nature of the game. It is very difficult to do on any level, but the constraints of homebrewing make it even more challenging. One trick for homebrewers is, instead of one 5-gallon (19-L) batch, try to split that into single-gallon (4-L) sizes. It isn’t an exaggeration to say that 20 components (be they 1-gallon/4-L jugs or 530-gallon/2,000-L foeders) is only a starting point for really getting into blending, which is the essence of these beers and something really unique to the style.
Another tip for homebrewers — cool in your kettle. Tiny versions of commercial coolships are a waste of time and money. In the US and in Belgium it takes approximately 12 hours for the wort to cool even with wintertime air temperatures. That’s tough to achieve with 5 gallons (19 L) even in a kettle, let alone a very shallow pan. If the wort cools too quickly it can have drastic effects on microbial growth and procession. Homebrewers can use any base style they like if they aren’t trying to use traditional lambic brewing techniques. Ultimately, I think the best recipes are going to be set up for long aging, which is pretty much a requirement for these beers. That means a wort that is very “unfermentable,” — so mashed quite hot if not using a turbid mash to achieve the same.
