Pressure Cooker Decoction

by Mike Retzlaff

Some 25 years ago, I read about a mashing technique which fascinated me.  The process involves using a pressure cooker to effect decoction mashing.  Instead of pulling a portion of the mash, heating it to a mash temp, resting, then heating to a boil (all while constantly stirring) before returning to the main mash, the plan is to use a pressure cooker.  This technique wasn’t new even back then.

The traditional decoction mash has been done based on three different systems.  The Bohemian, Vienna, and Bavarian systems are used to produce the types of beer usual in those regions.  In Bohemia, where lighter colored beer was the style, a shorter decoction boiling time of 10 to 20 minutes was made; in Vienna the decoction boil lasted about 30 minutes; in Bavaria a decoction boil would last as long as 45 minutes.  By variance of decoction boil times, a range of wort color can be made with a very simple grist bill.  Times change and many of the traditional breweries have reduced or eliminated decoction mashing to save time, labor, and fuel.  Today, in lieu of decoction mashing, we generally add all sorts of color malts to our grain bill to attain color and simulate that hearty malt flavor.

The decoction mash was developed at a time before malting science was well developed and understood.  Today under-modified malt is relatively hard to find.  Weyermann Malting in Germany, among others, still produces it but the demand for such malt isn’t high which makes it less available.  The good news is that modern Pilsner malt is widely available and perfectly usable with this technique.  All sorts of other normal malts work well also.

The decoction portion can’t be dumped directly into the pressure cooker as it would certainly scorch.  This portion is placed into a smaller vessel first as a bain-marie.  A trivet (or canning rack) is placed in the pressure cooker with some water.  It is heated as a water bath and the smaller vessel holding the mash portion is placed into the pressure cooker.  Once the decoction is heated to the target mash temp, it is rested.  After the rest, the lid is attached to the pressure cooker and heated again.  The cooker gets to work and the physics of the pressure cooker will cause the decoction mash temp to rise to about 250oF @ 15 psi.  The decoction will boil for 10 to 30 minutes, is cooled, and then returned to the main mash.  This cycle is repeated until the mashing is complete.

Why bother to go to all this trouble in the first place?  The reason is that decoction mashing doesn’t produce more malt flavor but instead, better malt flavor.  If skeptical, do a side by side comparison of a decoction mashed beer against an infusion mashed beer and you will immediately recognize the difference.  Decoction mashing also increases mash efficiency.  The pressure cooker eliminates the stirring of the mash with the associated weariness of arm, neck, and back muscles.  Manual stirring does not guarantee that the mash won’t scorch anyway.  You still have the choice of single, double, and triple decoction.  It all depends on what you’re trying to accomplish.

Decoction mashing also has its place among many beers normally not associated with European lagers.  Such candidates include Alt, Baltic Porter, English IPA, Dunkelweizen, and Scottish Ales.  A single decoction works well with Kölsch and Weissbier.  Even the standard American lager utilizes a cereal mash, which is a form of decoction, for rice or corn and usually done in a pressure cooker.

This technique is for those brewers interested in quality over speed of production.  An effective and efficient single infusion mash can take perhaps 1½ to 2 hours to complete.  Decoction mashing can take between 4 and 6 hours to complete – depending on the number of decoctions and the length of rests.

The standard for a “traditional” decoction mash is a liquor to grist ratio of 3.25 liters to 1 kilogram or 1.56 qt. per pound.  There isn’t any hand stirring involved during the heating in this method so we can tighten up on the ratio.  This also allows for pulling smaller decoctions.

Let’s deal with the set-up for a 5 gallon batch of Helles or Pilsner with a target OG of 1.050.  You’ll need a pressure cooker large enough to contain a trivet and a vessel capable of holding up to about 4 quarts of mash.  The internal vessel works like a bain-marie (or double boiler) and keeps the mash from direct contact with the bottom of the pressure cooker.  Direct contact with the heating surface can only result in a scorched mash.  Covering the top of the internal vessel with aluminum foil keeps the mash from spitting and plopping which may clog the pressure relief vent and generally make a mess within the cooker.  Add water to the pressure cooker after each decoction usage so it doesn’t run dry.

  • Start with 8# of crushed German Pilsner malt.  Mash-in with 10 qts. strike water (1.25:1 ratio) to achieve around 131 oF.  The mash volume will be about 3.14 gallons (12.56 qts).  Adjust the mash pH as needed.  Let rest for 25 min.
  • Pull the first decoction (2.8 qts.) and place in vessel.  Place vessel in the pressure cooker and heat water bath to bring the decoction to 150 oF; rest for 25 min. (check the temp of the mash; not the water bath) 
  • Put lid on the pressure cooker and heat.  Boil decoction at 250 oF @ 15 psi for 15 min.
  • Remove from heat and allow it to cool before venting pressure. (Venting quickly can cause the decoction to boil over [erupt] inside the pressure cooker!) 
  • Once the lid is off, remove vessel and return decoction to main mash.  After mixing, the temp should stabilize at 149 oF.  Rest for 25 min. 
  • Pull a second decoction (1.8 qts.) and heat to 158 oF.  Rest for 25 min.  Boil the decoction at 250 oF @ 15 psi for 15 min. 
  • Cool as before and add to the main mash which should stabilize @ 158 oF.  Rest for 25 min.
  • Pull a third decoction (2.8 qts.), seal lid and heat to 250 oF @ 15 psi.  No rest.  Cool before venting.  Add back to the main mash which should stabilize @ 170 oF.  Rest for 10 min.
  • Transfer to the lauter tun and process like any other mash.  Be sure to acidify your sparge water to 5.8 pH to alleviate astringency from the hulls.

Now, let’s deal with the set-up for a 5 gallon batch of Märzen with a target OG of 1.056.  The difference in this one is a bigger grist bill and subsequently, larger mash and decoction volumes.  Virtually everything else is the same.  Because the style requires a darker wort color, the grist bill has changed as well as the length of the decoction boil time.

  • Start with 6# of crushed German Munich (6 oL) and 3# of Dark Munich (9 oL).  Mash-in with 11.25 qts. strike water (1.25:1 ratio) to achieve around 131 oF.  The mash volume will be about 3.53 gallons.  Adjust the mash pH if necessary.  Let rest for 25 min.
  • Pull the first decoction (3.2 qts.) and place in vessel.  Place vessel in the pressure cooker and heat water bath to bring the decoction to 150 oF; rest for 25 min. (check the temp of the mash; not the water bath) 
  • Put lid on the pressure cooker and heat.  Boil decoction at 250 oF @ 15 psi for 20 min.
  • Remove from heat and allow to cool before venting pressure. (Venting quickly can cause the decoction to boil over [erupt] inside the pressure cooker!) 
  • Once the lid is off, remove vessel and return decoction to main mash.  After mixing, the temp should stabilize at 149-151 oF.  Rest for 25 min. 
  • Pull a second decoction (2.2 qts.) and heat to 158 oF.  Rest for 25 min.  Boil the decoction at 250 oF @ 15 psi. for 20 min. 
  • Cool as before and add to the main mash which should stabilize @ 158-160 oF.  Rest for 25 min.
  • Pull a third decoction (3.2 qts.), seal lid and heat to 250 oF @ 15 psi.  No rest.  Cool before venting.  Add back to the main mash which should stabilize @ 170 oF.  Rest for 10 min.
  • Transfer to the lauter tun and process like any other mash.  Be sure to acidify your sparge water to 5.8 pH to alleviate astringency from the hulls.

In both cases we’re using well-modified malt.  There is no real purpose for a mash-in of “blood temp” of 95 to 100 oF.  We’re starting with a proteolytic rest (131 oF) which will produce free amino nitrogen and degrade high molecular weight proteins into body & head supporting polypeptides.  The beta-amylase degrades amylose to maltose & glucose while amylopectin is reduced to b-limit dextrins.  We move up from that to a compromise mash temp (149 oF) to utilize both the alpha and beta amylase enzymes.  The next rest (158 oF) is to utilize the alpha-amylase to full advantage.  The last decoction is to raise the main mash to a mash-out temp.  Adding boiling water will do the same thing but while everything is out and being used, we simply take advantage of a little extra color, flavor, and aroma.

Many brewers act deathly afraid of what seems to be an ideal way of loading their wort with tannins and the associated astringency.  Polyphenols (tannins) are certainly a component of grain husks but these bad little dudes really aren’t encouraged to leach out until the mash goes above about 6.0 pH.  During the mash, the pH is mostly around 5.2 – 5.5 pH even during the boiling of the decoction.

I can still remember my apprehension when first starting an all grain single infusion mash.  After doing it a few times, I calmed down and it became second nature.  This technique is surely more complicated than a single or a step infusion mash and takes more time.  However, the quality of the resulting wort and the finished beer, is well worth the effort.

nota bene – A modern “Instant Pot” using a S/S mixing bowl as an inner vessel works nearly flawlessly.  Without the inner vessel, it would scorch just like a stove-top pressure cooker.  Newer Instant Pots also have a programmable control (sous vide function) to set the temperature of the decoction rest which simplifies things a bit. 

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