Lactobacillus "Kettle Souring" Corny Keg

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      Mick S

      Many brewers sour Berliner Weisse and other “lactic acid” sour beer worts in their brew kettles. It makes a lot of sense, because when the soured wort is subsequently boiled, the Lactobacillus bugs are killed and have no chance of infecting the main fermentation’s “clean beer” fermenter. There are, however, a couple of drawbacks to souring in a kettle. One is a lack of temperature control. Another is that it’s nearly impossible to exclude oxygen. Depending on the circumstances, these drawbacks can cause souring to take longer than desired and/or allow bugs other than the desired Lactobacillus strain(s) to take hold, resulting in a “garbage” aroma. So I put together a dedicated “kettle souring” corny keg to overcome these limitations.

      A big advantage to souring in a Corny Keg is oxygen exclusion. Corny’s are perfect for this, because using the Corney’s gas post input, they can be purged with CO2. This discourages less desirable bugs from growing.

      The other advantage is that using a temperature controller and one or two ferm-wrap type heaters, an ideal temperature can be maintained. A single wrap is enough to maintain 95F, which is ideal for Lactobacillus plantarum (Goodbelly drinks or shots, or Swanson pro-biotic pills). Two wraps are need to maintain 115F, which is good for most other Lactobacillus strains, or for mixtures (such as the naturally occurring Lactobacillus bugs on raw grains).

      keg with two wraps

      For my Corney, a friend cut off the bottom of the liquid dip tube and soldered a stainless steel slug in the end, creating a thermowell for the temperature controller’s probe, as shown below.

      diptube thermowell

      The new thermowell is installed just like the dip tube would have been (including the dip tube o-ring), except that the liquid post’s poppet is removed, to allow the probe and wire to come through the top of the post and into the thermowell. You can see the temperature controller’s probe wire entering the thermowell in the picture below. Also in the picture below, you can see a length of dental floss. On that day, the souring bugs were coming from some raw grains, suspended in the wort in a muslin bag tied to the length of floss running under the keg lid’s O-ring, and tied to the outside of the keg. Some will say that it’s impossible to get a “clean” lactic souring from raw grains, but oxygen exclusion and a high (~115F) temperature really keep the bad bugs pretty well under control. The resulting soured wort is more complex than a single Lacto strain would produce, and any slight funkiness is boiled and/or fermented away.

      top view

      In the picture above, you can see a pressure gauge on the gas post. Normally, Lactobacillus doesn’t create CO2/pressure, but other bugs, particularly wild yeasts, can. The pressure gauge isn’t absolutely necessary, but it’s nice to have visual confirmation that everything is in order.

      In the picture below, you can see the temperature controller indicating that the wort is being held at a steady 114/115F. But again, if you’re using L. plantarum, 95F is better.


      To keep the heat wrap(s) from having to work too hard, I built a “Lacto Lounge” out of styrofoam sheeting and construction adhesive. The result is just a styrofoam box that can be placed over the whole thing to hold in some of the heat (like a mini-fermentation chamber) as shown below.


      That’s pretty much it. In addition to Lacto soured beers, I’ve also used this rig a couple of times for making Lacto fermented hot sauces.

      • This topic was modified 4 years, 7 months ago by Mick S.

      ---Mick S (aka VikeMan)

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