Decoction mashing

a micro-FAQ by Marc de Jonge (dejonge@geof.ruu.nl)

Every now and then questions on decoction mashing come up in the Homebrew Digest, for that reason I've put together this small FAQ file. I hope this is enough to get you started. If you have any comments or questions on the contents feel free to mail me at the above address.


What is decoction mashing?

In essence decoction mashing is a temperature controlled mashing method that differs from the normal 'step-infusion' mash only in the way the heat is applied. The difference is that in decoction mashing part of the mash is boiled in a separate kettle. The boiled part is added back to the mash to achieve the required temperature rise. The effect of the boil on the final beer is very strong. In my opinion decoction mashing is important (together with the choice of malt and yeast of course) for achieving the characteristic malty taste found in many of the best commercial beers.


What beers are made with decoction mashing?

The decoction method is the preferred mash method for many beer styles originating on the European continent. For example: Pilsner and pilsner imitations (From Pilsner Urquell to Bud) Almost all german beers (maerzen, bock, weizen, some alts, rye, dortmunder) Some of the lighter Belgian ales (De Koninck, Palm, Rodenbach)


Advantages of decoction mashing

The following advantages are in my opinion more important for homebrewers:

Disadvantages


Some general considerations

First, a table with some temperatures for the unmetriculous:
35C   =   95F, glucanase rest (breaks down gummy stuff)

52C   =  127F, Protein rest.

63C   =  145F, Beta amylase rest for dry beers (pils).
.
. (anywhere between these temps is ok)
.
67C   =  153F, Beta amylase rest for thick beers (bock).

72C   =  158F, Alpha amylase rest for dry beers (pils).
.
. (anywhere between is ok)
.
75C   =  167F, Alpha amylase rest for thick beers (bock).

78+C  =  172+F, mash out range.

Strike temperature:

The examples that follow give an indication for the strike temperature, getting this right is often more art than science. In practice (when you use 2.5L/kg or 1.3qt/lb) you add the water at a temperature of 7C or 12F higher than the mentioned value, just like you would for an infusion method.

Calculation of boiling volume:

In the following examples I've indicated what proportions of the mash should be boiled (roughly 1/4 to 1/3). When taking out this fraction, you could try leave behind as much clear wort as possible. However, the risk of scorching increases if you are to zealous. My preferred method: stir well and scoop out the right amount without worrying. This does not go for mashing out, when you only take the clear liquid off the top.

An approximate formula for calculating the boiling fraction F is the following:

   T1-T0
F= 
TB-T0-X

Some practical examples

Obviously decoction mashing methods can vary as much as anything in brewing, but here are some practical examples. I've used the first three myself, the last is a traditional example.


Short 1-step method

for simple pilsners, koelsch, alt and even pale ales that require a bit more malt flavour. This method takes approximately two hours.

Preferably use a good 2-row malt, not too many starchy adjuncts


Average 2-step method

for Belgian pale ale, German pilsner, Munich styles and Bavarian wheat beer. This method takes 2.5 to 3.5 hours, depending on the grist.

3-step method

for extremely poor quality malt and strange adjuncts. This method can take 3 to 6 hours.

(in this example the grist is 45% pilsner malt, 35% buckwheat and 20% unmalted wheat, should I deposit the name buckwhiter?)



3-step traditional

[commercial example from :De Clerck, Leerboek der brouwerij, Leuven, 1962], this one takes 5 to 6 hours. It is more or less the method used for Pilsner Urquell.
Marc de Jonge (dejonge@geof.ruu.nl)

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Spencer W. Thomas (spencer@umich.edu)