What is Decoction?

Boiling
Boiling

Toward the end of the fall beer season, I like to look back and reflect on how great Oktoberfest beers are.  They have a great malty, almost burnt-caramel flavor to them.  This is because many of these beers use a process called “decoction”.  This is when about 0ne-third of the resting mash is scooped out, boiled, then returned to the original mash.  This raises the temperature to a specific level, achieving a higher resting temperature to activate different enzymes.

Decoction mashing was widely used in Europe, specifically Germany, before the use of thermometers because taking out a portion of the mash and boiling it (a constant temperature) successfully allowed the specific temperature values to occur.  In addition to this, boiling the grains also made extraction of the starch easier by breaking the cell walls of the grain.  Today, this is not as necessary, because most brewing grains are well-modified, so the starches are easily available for starch to sugar conversion.

Oktoberfest
Oktoberfest

Kind of a “side-effect” of this style of mashing was the introduction of complex, strong caramel flavors from the boiling, called a maillard reaction, producing melanoidins.

These are some of the flavors found in several malt-forward beer styles, such as Oktoberfests, marzens, or bocks.  Samuel Adams also uses this type of technique for the Boston Lager.

The decoction process is not used as much today because it is extremely time consuming (up to 3-4 times as long), and is logistically very difficult in large scale breweries.  For the homebrewer, however, it may be a process worth exploring.

Have you heard of decoction mashing?  What is your take on the process?

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