Wednesday, February 20, 2013

Wild Yeast Culture Experiments - Homebrew Horny Tank

In a 2007 NHC Presentation, Vinnie Cilurzo (of Russian River Brewing) suggested homebrewers try keeping a Horny Tank (inoculation tank) for maintaining mixed cultures. Used in many of the sour breweries in Belgium, he thought it may be a good way to keep a mixed culture viable without keeping a starter or brewing on a production schedule. A run-down of the process:
  1. Start a normal batch of sour beer with a mixed culture.
  2. Allow the beer to ferment in a plastic bucket for at least three months.
  3. Any time after three months, brew another batch of wort.
  4. Transfer the first batch to secondary for further conditioning, leaving behind a bit of liquid, the yeast slurry, and trub.
  5. Immediately add fresh wort to the fermentor with the wild yeast slurry.
  6. Repeat.
I started my own "Homebrew Horny Tank" last October. I brewed a blonde wort with a traditional turbid mash and inoculated the batch with several doses of revitalized, commercial bottle dregs. I plan to mature the beer in the bucket, tasting every few months.

The fear in using plastic buckets to condition a wild-fermented beer is that the bucket allows too much oxygen diffusion, resulting in excessive acetic acid production. After doing some research, it seems this fear is perpetuated by a single source. Although this article is an incredible resource for brewing sour beer, I believe the plastic bucket deserves a second chance.

To be safe, I will only disturb the beer to take samples, and I will purge the headspace with CO2 after sampling. When the beer is "ready", or if it displays the slightest amount of acetic acid, I will transfer it into a keg, leaving behind about a quart of beer, trub, and slurry. I'll then immediately transfer another batch of wort into the bucket and start the experiment over.

So far the results have been positive. Surprisingly, the bugs from the bottle dregs made quick work of the wort, completing primary fermentation in nine days and forming a pellicle in about two weeks. My first (and most recent) sample was three months after brewday (1/13). As expected, the beer tasted very young, with only a slight prickle of acidity. The aroma had a heavy sulfur note, which I believe will mellow with time (I've had sulfur aromas in a few other young sour brews). More importantly, the beer showed no signs of acetic acid production in the aroma or flavor. So far, so good.

In keeping with the theme of this blog, I want to find mixed culture methods that will translate well to a commercial scale. My mixed culture starter method could be utilized in a commercial brewery, but I believe it will often not be financially or logistically feasible. The brewery may not have the space or funds to allocate a fermentor or yeast propagation vessel specifically for wild yeast. At the same time, banking a special blend, or buying several strains of yeast and bacteria to produce a relatively small quantity of beer can also be extremely expensive.

In addition to those producing only sour and funky beers, I believe the horny tank technique could also work for commercial breweries producing them in limited amounts. Though still taking up fermentor space, it allows the brewer to consistently produce sour beer from the culture, rather than just store the slurry. The horny tank is flexible, allowing the brewery to keep a batch of fermenting sour beer and a viable culture in the same vessel. Though some may call this method sacrilege or assume its a shortcut, the time, resources, and money required to create a barrel-aged sour beer often makes them prohibitive. As homebrewers are creating fantastic funky and sour brews in glass, plastic, and stainless, I believe commercial brewers can do the same.

I will continue to make updates on this experiment as well as others in this series. To be honest - I don't see the series ending. I hope to continue playing with sour beermaking techniques, learning new techniques, finding new bugs, and creating new flavors. Let's face it - you can never have enough good sour beer around the house!


  1. So, it has been nearly 4 years, how has this worked out for you?

    1. Its still my favorite method of making sour beer! I like how the culture matures versus in a 1 gallon jug.

      I have switched to a glass carboy. As the bucket gets older, it lets in more air. Plus I can see how much trub is accumulating.

      Sadly, I haven't had time to brew often enough to keep this going. We're starting a brewery that will (hopefully) be open this year! I do plan to incorporate this method commercially in an oak puncheon, eventually in an oak foeder.

      Let me know how it works for you and how you tweak your process.


    2. We've been doing something similar with a solera in a former Pinot Noir barrel, we've only been emptying it about half way before topping it up with sacc fermented Saison. We do an exchange every 6-8 months. So not quite the same thing. I was thinking of starting something along the lines of a horny tank like this in a carboy. I'm a bit concerned about it as a number of my wild beers get way too much ethyl acetate after 8-10 months though I suppose if I just make sure I'm not too lazy to brew replacement wort before then it shouldn't be an issue.