Step Mashing Concoctions, Infusions, Decoctions

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I've long been a fan of European lagers and some years back had the pleasure of spending a wonderful summer in Munich with friends. We lived up the road from the famous Lowenbrau Keller and when opportunity presented itself, frequently enjoyed sampling the culinary and beer related offerings to be found there.

Memories of Munich
In recent months I have been attempting to replicate those delectable flavors from that memorable Bavarian summer by brewing some lagers and hybrid ales. These include a Munich Helles, a Munich Dunkel, two Vienna lagers, a German pilsner, a Kolsch and an Altbier.
In researching these styles of European beers I noted a trend. Traditional methods including step mashes are commonplace, being used by many breweries. These breweries often have rich histories with adherence to centuries-old arcane purity laws. They are not typically associated with experimental techniques. Perusing the database of award winning recipes from the "American Homebrewers Association" revealed a similar trend in mash profiles. It would appear that both traditional brewing methods and competition success on the national level support the use of a step mash for certain styles of beer.

Step Mashed Beers. Brewed for Science!
The counterpoint to this anecdotal support for step mashing is the large number of well-versed and respected brewers who will quite reasonably argue, given the nature of fully modified modern malts, that there is little if any benefit to their use.
I would ask the reader to shelve their thoughts relating to this debate for the time being. The purpose of this article is primarily to illustrate the processes involved in carrying out a step mash, whilst largely ignoring the meaty topic that is the scientific basis for their usefulness or for that matter, their redundancy.

My Stove-top setup for step mashing
Having a metal mash-tun makes incorporating a step mash into your process a lot easier. As a happy proponent of single vessel brewing I view this as an all-too-often overlooked advantage of this brewing method, one that I feel is largely under-utilized by the majority of single vessel brewers. Step mashing is of course possible regardless of ones all-grain setup. Options and corrective measure are however more limited if using a plastic mash-tun.
Excluding heat exchange recirculating mash systems (HERMS) and recirculating infusion mash systems (RIMS) of which I have no experience and only a rudimentary understanding, there are four ways to carry out a step mash. An accurate, calibrated thermometer and correctly dialed-in brewing software are indispensable in my opinion, if a step mash is to be undertaken.
Methods for carrying out a step mash
  • Directly heating the mash-tun
  • Infusion step mashing
  • Decoction mashing
  • A hybrid approach incorporating some or all of the above

Step mash via direct heating

One big advantage of step mashing via direct heating is that it requires no additional pot. Disadvantages to this approach are that it is only possible if using a metal mash-tun, and that constant stirring of the mash is required during the application of heat.
A mash is a poor thermal conductor and constant stirring is needed if scorching the mash or denaturing critical enzymes via non-uniform heating is to be avoided. The measured mash temperature must be representative of the mash as a whole to prevent overshooting the desired rest temperatures. Constant stirring maintains this required thermal homogeneity.
When step mashing this way I find it best to kill the heat 1F shy of your planned rest temperature. The residual heat in the pot will continue to warm the mash the last little bit of the way. It's analogous to driving up to a red light: you take your foot off the gas and allow the residual kinetic energy to coast you the rest of the way there.
With the insulated lid removed and constantly stirring a full-volume mash, ramping the temperature to each rest takes quite some time. Owing to its low melting point, placing insulation around the mash-tun is not safe on my setup when applying direct heat. My heat source is a natural gas stove. Reflectix insulation exposed to naked flame is an obvious fire hazard worth avoiding.
Infusion Step Mashing
Step mashing via infusions of near-boiling water requires much less work and attention from the brewer. Stirring is only needed when adding the pre-planned volumes of water to reach the desired temperatures. The mash-tun can remain insulated throughout and a metal mash-tun is not required.

Heat source. Insulation. Infusions at the ready. False bottom for use with my BIAB setup
The Process.
  • The full water volume is collected in the boil-kettle. Minerals are added to target the desired water profile.
  • Sodium metabisulfite/ Potassium metabisulfite is added to eliminate chloramines and chlorine.
  • A measured volume of water is drawn off to a second pot: the HLT.
  • The volume in the HLT is calculated to provide all the water needed for infusions and any planned sparge. (I typically do not incorporate a sparge step into my brewing.)
  • The water in the HLT is brought to a boil and a simmer maintained with the lid on.
  • Strike water is heated to target and dough-in completed as normal hitting the first rest temperature.
  • Pre-calculated volumes of the collected boiling water are added to the main mash, heating it to the next planned rest temperature.
  • The mash is stirred thoroughly while adding the hot water to ensure homogeneity and representative temperature readings.

Confirming correct rest temperature
If you carry out infusion mashes this way it is impossible to overshoot your final mash volumes, an oft touted disadvantage of infusion mashing which can be particularly problematic if a sparge is planned. If you come up a bit cool on the last infusion step you can take corrective measures. The insulation is simply removed and direct heat is applied to the mash.
Decoction Step Mashing
The third way to carry out a step mash is via decoctions. This is a little more complex and time consuming but follows a similar principle: the addition of near-boiling material to the mash to raise its temperature. No direct heating of the mash is involved.
  • A thick portion of the mash is removed to a second pot. This is the decoction.
  • The decoction is heated.
  • An optional step is to carry out a conversion rest on the decoction itself before heating it further.
  • The decoction is brought to a boil and subsequently boiled for a period of time. Once again, constant stirring of the decocted portion of the mash is needed when heat is applied.
  • The decoction is then returned to the main mash raising its temperature to the next planned rest temperature.
  • This process can be repeated as needed depending on the number of steps.

Pulling the Decoction

Boiling the Decoction. Smells great!

Additional issues related to decoction mashing
  • My brewing software typically under estimates the required decoction volume.
  • Mash pH appears to be slightly lower, (~0.1) than planned when a decoction is used.
  • I have noted heat loss from the primary mash while pulling the decoction.
The first two issues can be addressed during the planning stages of a brew. The heat loss can be remedied with a corrective application of direct heat to the mash. One more benefit to having a metal mash-tun.

Mash pH is measured when the mash is at its maximal volume
I typically incorporate a combined approach when carrying out a step-mash. There are of course pros and cons to each method that should be considered.
  • Infusions are easy to calculate, prepare and carry out.
  • Directly heating the mash-tun is very accurate but more work is involved. Ramping duration, (the time spent going from one rest to the next) is also significantly longer than with infusion step mashes.
  • Decoction mashing takes a bit more trial and error to work out the details.

Recently used example of a hybrid mash profile incorporating infusions and direct heating
[*]Dough-in at beta amylase rest*
[*]Infusion of near boiling water to reach a combined rest
[*]Infusion near boiling water to reach alpha amylase rest*
[*]Direct heating to reach mash-out rest

Recently used example of a hybrid mash profile incorporating an infusion, decoction and direct heating
  • Dough-in to hit a short, high temperature protein rest.
  • Infusion of near boiling water to reach beta amylase rest*
  • Single decoction to reach alpha amylase rest*
  • Direct heating to reach mash-out rest.
I'll be honest here, my perspective on step mashing is that it's fun to do. I enjoy the added planning and measurement that are involved. It presses many of my inner-geek-buttons. More importantly, I am enjoying the resulting beers where a step mash was used. If adding a little complexity and additional time to your brew-day is something that doesn't phase you, I would encourage experimenting with step mashes to see for yourself what they can do for your beer.
* Note: The names of the rests are chosen to indicate the dominant enzyme at work.
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Very cool and simple explanation of decoction mashing. I'm not sure I'll be giving it a go as I follow the Denny Conn "As Simple as Possible" way of brewing, but I never understood it fully until now.
Cheers & Thanks
This gets me to want to try infusion mashing again! I stopped doing that when I always hit the wrong temperatures. My mash probably dropped a degree or two in every step so i always ended up a couple of degrees short. But it made brewing more fun and "hands on" than just watching tv for 90 minutes...
Dangit! Where's your recipes for the Munich helles, Paulaner Weisn Octoberfest and more! Lol
Nice article. I was lucky enough to visit Octoberfest 2013. What a great trip.
Great *sigh*, another trip added to my bucket list. Thanks for a very well-written article Gavin.
Great job as usual Gavin.
While the sources are a number of years old, decoctions and step mashes are historically attributed to high conversion efficiencies.
Decoctions can be attributed to higher gelatinization as the thick mash is heated.
I doubt the accuracy of such claims in regards to modern malts and I'm sure the fine milling employed by biabers does much the same as more surface area is exposed.
Absolutely great article! I am an American army officer living in Germany and I love beer! I started brewing after I left Germany in 1995. My first visit was in 1988 and I loved it, several tours later I now live an hour southwest of Frankfurt and visit southern Germany often. The grain is so fresh and cheap compared to US prices. I am working on perfecting my step process so I can brew these wonderful beer back home in Oregon. I love Helles, Kloster Dunkel, and Alt.
I have done a step mash for a partial mash. Direct heat made it simple. I did it because of tradition. Now I'm interested to try that recipe as a single infusion. I've pretty much perfected it so I should be able to tell a noticeable difference (better or not).
Gavin, great article! I too was stationed in Germany (78-81) and came to love her beer, especial those from Bavaria. One question...we've always been told not to heat the mash to more than 170*F for fear of releasing tanins from the husks and creating a grainy or astringent taste. How is this prevented when boiling part of the mash in the decoction?
This is my understanding of why that does not occur with a decoction. Hopefully I am not too off-base here.
To extract astringency causing tannins, two things are needed.
Temperatures in excess of 170F and a pH in excess of 6.0 (Roughly)
With a decoction the temperature is ~212F but because the decoction is so thick, the pH is kept well below this threshold and astringency should not be noted in the resulting beer.
I do step decoctions with a HERMS system & it helps a lot.
Basically, I pull 1 qt per lb of grain for each decoction step. Do a brief (10-15 min) sacc rest of the decoction prior to boiling & then adding back to the MLT.
I only need to get relatively close to the next step rest, within 3-5 degrees & then just use the HERMS to get the liquid mash to where I want it & then hold it there.
And I completely agree with you about decoction mashing relative to the argument about fully modified malts.
The decoction is not done for starch to sugar conversion as much as giving the finished beer that body & flavor that is so obvious in a decocted beer.
I have tried to do single infusions with 2-3% malanoiden and it just isn't the same. You have to boil the heavy mash. No other way around it in my opinion.
I'm a little surprised how thin your decoction pull looks. Normally I grab it thick enough that the grains are not submerged while boiling (constant stirring obviously). One thing I like is how much efficiency I gain through decoction. My last Helles I got 84%, compared to 75% with infusion.
With full volume mashes you're starting with a thinner mash to pull from. Takes a bit more effort I guess to get the decoction sufficiently thin. My decoctions are adequately thick.
I see no difference in efficiency with decoction -v- non decoction mashes. That is entirely expected given my after the fact calculated conversion efficiencies on my setup. There is really nowhere to go in that regard.
I am not aware of any data in support of the idea that a decoction mash will increase mash and subsequent brewhouse efficiency. I would be interested to learn more if you have a link to share. Thanks for the feedback. Much appreciated. . Shoot me a pm or post to this thread