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

Because of the boiling, cell walls of the grains are destroyed. This allows an easier access for the enzymes to the starch. As a result the efficiency of decoction mashes is generally higher than for other methods. (This is probably the reason almost all megabrewers use this method)
Grains that need gelatinizing at high temperatures can be boiled separately in one of the decoction steps (can be useful if you use for example rice or rye).

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

Boiling part of the mash extracts more flavour from the grains. Especially beers made with a lot of pale malts improve by this effect.
A slight Caramelization can occur during the boil, giving a fuller flavour to the beer (I don't know why, but the effect of adding dark malt is not quite the same).
Part of the protein already coagulates during mashing, which helps to produce a clearer beer.
The method allows stepped-temperature mashing in a tun that cannot be heated (picnic cooler, or 6 yards high wooden barrel)

Disadvantages

The traditional decoction methods are designed for very poor quality malts, as a result they often require very long mash times. (Note that for amateur brewers this is not an issue because it is almost impossible to get these poor malts.)
Splashing the hot mash may cause some additional HSA.
Care must be taken to avoid scorching the mash when it is boiled, this means the decoction method requires more attention and work (stir when you heat).
pH must be checked and corrected to avoid extraction of tannins from the husks (anything below appr. 5.7 is ok)
Special care must be taken for mash-out (which is of course optional anyway): boiling the grains the last time may release some more starch that will not be converted because you've just wiped out the enzymes. The traditional work-around is: boil only the clear liquid for mash-out.

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

TB is the temperature of boiling mash (near 100C/212F)
T0 is the starting temp
T1 is the required temp. (Units F or C, don't mix them).
X depends on your mash setup, but 10C or 18F is a typical value, you can adjust this if you find you need to boil a lot more or less to hit the right temperature.

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

Strike temperature 64C, stir well and rest for 20'.
Stir and immediately put 1/3 of the mash in a pan (the remainder stays at 64C). Slowly heat the pan to 73C, rest for 20'.
Bring to boil and maintain a good rolling boil for 15-30', beware of scorching.
Add boiling mash back to the rest, stirring well until temperature is around 72C. (Normally you won't need everything you've boiled, add the remainder when it has cooled down a little). You can add dark malts at this time too, if you want to keep the dextrin level high.
Rest until saccharification is complete (probably between 30' and an hour, test the clear wort for starch residue).
No mash-out, start sparge immediately.

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.

Strike temperature of 53C, stir well and rest for 20'
Stir and take 1/3 of the mash. (If you use a large proportion of unmalted grains you can take less of the mash and add water and dry crushed grains to make up 1/3 of the total volume). Heat to 72C, rest for 20' (malt) to 40' (malt+grains).
Bring to boil and boil for 15-30'
Add back to reach a temperature of 65-67C, rest 15-35'
Take 1/4 of the mash, boil for 15-30'
Add back to reach a temperature of 70-73C, rest until saccharification is complete (30'-1h).
No mash-out, start sparge immediately.

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?)

Strike water malt and wheat for temperature 53C, rest for 40'
Boil a 'porridge' of buckwheat and water during this rest.
Add this to the mash, for a temperature of 63C (I wanted a dryish beer), and rest for 35'.
Heat 1/3 to 72C, rest 30' and boil 25'.
Add to mash for a temperature of 70-72C, rest 50'.
Take clear liquid off the top, bring to boil and add back for mash-out (5').
Start sparge.

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.

Strike for 35C, rest 20'.
slowly (20') heat 1/3 to 65C, rest up to 25'.
slowly bring to boil, boil up to 25'.
Add back, T=52C, rest 5'.
slowly heat 1/3 to boiling, boil up to 25'.
Add back, T=65C, rest up to 50'.
slowly heat 1/3 to boiling, boil 5'.
Add back for mashout (77C).