Fermenting a Kolsch Under Pressure


By Brad Probert

Fermenting Under Pressure

As pressure-capable fermentors become more affordable and available in the homebrew market, people are exploring fermentation under pressure.  But just because you have a fermentor that is pressure capable, doesn’t mean you need to start pressure fermenting everything.  Just like any brewing process, you should understand the reason for it, and then use it if/when appropriate.
The main effect of fermenting under pressure is that it can affect the yeast flavor profiles (suppress ester production).  So if you have a fermentation that you want to decrease ester production, fermenting under pressure is a tool you can explore.  The most prevalent use of the pressurized fermentation technique is fermenting with lager yeast, but at room temperature instead of cold temperature.  That’s because fermenting lager yeast warm is typically avoided because of the undesirable esters created from those yeasts at warmer temperatures.
Each yeast is different, and how well they respond to pressure is going to be different.  Plan your fermentation parameters based on other learnings, but recognize the results with your yeast might not be exactly the same.  With that in mind, I crafted a pressurized fermentation experiment.
I had a great experience in Cologne several years ago with some fresh Kolsch while sitting at the open-air Fruh brewpub.  I’ve tried to recreate that beer so many times and have never been pleased with the results.  As much as the yeast flavor is a characteristic aspect of Kolsch, I don’t remember the white-wine-like flavor in that beer in Cologne.  But every Kolsch I’ve brewed, that flavor overpowers the experience for me.
Full Batch Brewing Fermenters


I wanted to see if the ester-suppression phenomenon of fermenting under pressure could subdue the yeast flavors I wanted to minimize.  So I made a 12-gallon batch of my Kolsch recipe and split it 3 ways into separate FermZilla All Rounders.  One batch was fermented at basement temperatures (70F) with a blowoff tube connected, and the comparison batch to this was fermented also at 70F, but after 24 hours, a spunding valve ramped up the pressure to 14 psi for the remainder of the fermentation.  The third batch was fermented at 54F, with the same spunding approach of no pressure for the first 24 hours, then up to 14 psi from that point on.
Below are the recipe details.  Not a traditional Kolsch grain bill, but I wanted to get a clean malt taste from US 2-row (I find Pilsner malt can sometimes have a sweetness).
  • 12-Gallon batch size
  • 17.5 lb Briess Brewer’s Malt
  • 2 lb White Wheat Malt
  • 1.5 oz Perle pellets @ 60 min for 16.1 IBU
  • 1.5 oz Hallertau Mittelfrueh @ 15 min
  • House water through 3-pass filter + K-meta tablet then adjusted (Ca 37, Mg 10, Na 37, Cl 37, SO 63, HCO 116) + Lactic acid added for pH 5.28 in mash tun
  • Mash 145F for 40 min, 158F for 20 min, 168F for 10 min
Brew day went well, with no issues, other than a higher-than-expected mash efficiency of 87% (1.049 OG).  And being the middle of summer, I couldn’t get the “room temperature” batches as cool as I wanted, so they were fermenting at just above the top of the recommended temperature range (65-69F), at 70F. 
With the two fermentors at warmer temperatures, fermentation ripped off and chewed through ~70% of its gravity drop in the first 48 hours, then went through a very long and slow gravity drop over the course of a couple weeks before finally flatlining on my Tilt to let me know it was finished.  On the batch that had the spunding valve pressure turned up, it hardly slowed the gravity drop at all.
The batch fermented cold had a much more controlled gravity drop at the beginning, and then it too had a long tail over a couple of weeks before its gravity drop stabilized.  But overall fermentation time was roughly the same as the much warmer batch.
And contrary to my previous findings of pressurized fermentation slowing the fermentation rate, the two batches that fermented under pressure actually reached their final gravities sooner than the one batch that fermented with a blow-off hose attached the whole time.
The un-pressurized batch that fermented at room temperature with a blow-off tube had a unique gravity trend.  The gravity looked like it was about finished dropping, and then it got a second life and continued to ferment for several more days.  It ended with an FG of 1.005 (89% apparent attenuation), in contrast to my other two batches with an FG of 1.013 & 1.014. 


Overall, I had interesting results.  First off, the un-pressurized batch that fermented at room temperature developed some astringent tastes.  Maybe this picked up some sort of infection, and that explains the low FG as well as the off-flavor.  This wasn’t a variable I was specifically trying to test, but perhaps a pressurized headspace would be better at fending off unwanted contaminants.
On the two pressurized batches, there was very little flavor difference between the one fermented at 14 psi & kept cool at 54F and the one at 14 psi & left at 70F room temperature.  Both of these had a very clean taste, with the cold fermented batch with slightly less aftertaste.  But I couldn’t reliably differentiate these two with a blind tasting.
The biggest finding I had was from a non-pressure-related variable.  I brewed with a different target brew water profile than previously.  And it definitely seems the white wine notes I was getting on previous attempts was likely an interaction between the yeast and my brewing salts.  With that taste out of the way, I realized I need to go back and re-vamp my grain & hops combination to arrive where I want to go.  But I do know that when I do, I can get there without having to ferment cold- as long as I ferment under pressure.


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