Kettle Souring

I got the tip on how to do this from Tim at the Dry Dock Brewery.  He’d given us a taste of his “Regal Tang” so I asked where the pineapple and mango flavors came from.  Turns out he’d used yoghurt to pitch lacto into hot wort, left it overnight, then boiled with hops the next day.

So I tried a batch.  I mashed, ran off the wort, boiled it for ten minutes, stuck a thermometer probe into it and cooled it to 120 degrees.  At 120 degrees, I pitched a couple teaspoons of my sourdough starter into it, insulated the heck out of it (as best I could), then left it overnight.  The next morning I checked the pH.  It was about 4.1, I wanted in the vicinity of 3.5.  I let it set a couple of hours then checked again.  4.0.  So I turned my hot plate on low.  The wort began to warm very slowly.  Seeing that it wasn’t about to get away from me, or so I thought, I went upstairs to take a shower.  When I came back to the wort, the pH was 3.9, okay, but the temperature was 151 degrees.  I’d killed my lacto.  So I boiled, fermented and still got a pretty good beer out of it, not as tart as I’d like but still nice.  Unfortunately, I didn’t take pictures.

New procedure involves my Inkbird temperature controller.  It controls both heating and cooling.  I generally use it to control my fermentation chamber – it’s holding the temperature above room temp for my 90-degree Belgian Saison.  Next batch I run my hot plate through it controlled to 120 degrees (50 celsius) with the probe in the wort.  The controller in Celsius mode holds the temperature to +/- 0.3 degrees, effectively 1 degree Fahrenheit, and the temperature is adjustable to 0.1 degree Celsius.  Interesting because the actual conversion of 120 degrees F is 48.9 degrees C.

So why kettle sour when there are other alternatives such as sour mashing, Brett fermentation, wild yeast, sour blends.  The literature will tell you, at least the snobbish parts, that kettle souring lacks “complexity” compared to other souring methods.  Here are my reasons for kettle souring above the others:

1.  It’s very controllable.  Some other methods give you what you get.  Souring in the kettle leaves you in control – you can stop the process at whatever level of tartness you want for the effect you want.  I’m even thinking of a very short kettle souring for my next batch of Irish Stout, since Guinness is rumored to use stale (read old), slightly soured beer in their blending process.

2.  You don’t contaminate equipment.  You boil the kettle after souring, killing off all the lacto before it can infect your next batch.

3.  It’s fast.  No waiting for a year or so for your Brett or your Lacto pitch to sour the beer.

4.  You can even control what you pitch.  Yoghurt works, sourdough starter works, natural sauerkraut would work, even pitching grains would provide lacto.

5.  Less chance of the enteric bacterial stench.  No need to stink up your work area.

6.  Most important, I like the results.

Sourdough Blonde – An Adventure in Kettle Souring

Sometime last year Tim, the head brewer at the Dry Dock South, led me into the back and handed me a sample from one of the fermenters.  It was nice!  Tropical fruit flavors, some lactic smoothness on the tongue, tart and clean.  So I asked the secret and he told me, a pitch of organic yoghurt once the wort had reached 120 degrees then keep it warm overnight.  By morning the pH was in the 3.5 range.  From there, boil as usual.  So I tried it.


This is Sourdough Blonde at eight days in the bottle.  Instead of the yoghurt pitch, I used a couple teaspoons of my sourdough starter as the lacto source.  She came out very nice, not as tart as Tim’s due to an error on my part, more on that later.  But the tropical fruits – pineapple and mango – are there, some malt flavor is still to be found despite the souring.  It has some body and is a pretty beer.  I’m happy with it!

My error was temperature control during souring.  I chilled the wort to 120 degrees, pitched my sourdough and insulated the heck out of the kettle to keep it warm.  By the next morning it was in the 90’s, warm enough for lacto but cool enough to allow some unwanted bugs to take hold.  So I started applying heat using a hot plate.  It looked as if all was well, the temperature was holding between 110 and 120 degrees F so I went to take a shower.  When I came back, it was 150 in the kettle, all my lacto were dead.  The pH had only dropped to around 4 but there was nothing to do other than to continue processing.

She came out good, though.  And I got a two-stage temperature controller so next time, the hot plate will cut off at 120 degrees.  More on kettle souring later. Here’s the recipe: