It was in 2016 where I got involved with the ingenious founders of the German Brewing forum where we set out in anger to tackle brewing bavarian lagers with homebrew setups. The result was a rather interesting paper (On Brewing Bavarian Helles) which showed that reducing oxygen pickup on the hot side had stunningly positive effects. Whatever your views are, there is a substantial body of work in the professional literature (Narziss, Kunze, Fix amongst others) explaining the chemistry. One of the founders created an excellent site (The Modern Brewhouse) on the topic.

Initially, we thought that decoction mashing was off limits due to the technical challenges implementing a system avoiding excessive oxygen intake due to scooping the mash around. I am not sure most homebrewers would like to invest in a postive displacement pump capable of operating at 100 °C either.

Eventually, a few people kept on experimenting and had good results with the following method, allowing for decoctions avoiding the transfer of the hot mash.

  • Dough-in is rather low, usually at 35 degrees Celsius with a grain:water ratio of 1:2,5
  • The mash then rests for 10-30 minutes
  • 10-20% of the total volume is run off into a seperate vessel (Enzymauszug) which is used later to convert the remaining mash (usually 10% is sufficient)
  • The mash is then converted as usual with typical rests at 50, 65 and 70 °C
  • After conversion the entire contents are brought to a boil (95 – 100 °C) for typically 20 minutes (I tend to be happy keeping it at 95 °C).
  • The decoction is then cooled to ca. 65 °C by adding the remaining cold water until a consistence of 1:4 is achieved.
  • Then the saved mash (enzymes) is added and a further conversion of the newly released starches during the boil occurs, typically in 15 minute steps for each, 65, 70 and 78 °C.
  • The contents are then sparged as usual

The procedure is rather lengthy. It typically takes about four hours. Efficiency will take a boost since it allows for a complete conversion of all starches. One drawback is that the Beta-Glucans may not break down completely, thus it is generally employed for well modified malts (which should not be a problem for home brewers).

There are some variations on this theme… more about this later.

Happy brewing!