It’s not a secret that most Bavarian breweries use a process called “Decoction Mashing” for converting the grain’s starches into the necessary sugars. Schneider and Augustiner certainly do!
The problem with this type of process, is for newcomers to understand how to influence body and fermentability of the wort. There are a lot of instructions out there who say… just boil the grain. That’s not very good because one major mechanism for controlling the body of the beer is ignored. Programs like “beer smith” have no provision for recording or planing the conversion of the decoction itself. That’s a huge minus in my books. It will make it very hard to replicate unless one always uses the same method or takes notes and attaches them (becomes tedious over time though).
The thing to understand is that one does 2 mashes actually. There is the main mash and the mash of the decoction itself. A very good way of doing this is to dough in around 38C and pull the first decoction after the grain has sufficiently hydrated (30 minutes to an hour usually). This first decoction is the most important. It’s critical it is converted correctly. So you need to perform a protein rest around 50C – 55C and then perform a combined rest for saccharification (usually in the 64C – 72C) range. For a very sweet beer, use the upper temperature range. The conversion should be complete and pass the iodine test before one can proceed to the boil. I prefer to give this an ample rest, just like the one used in a single step infusion mash, usually 30-60 minutes, before I proceed.
And now to the boil.
Boiling the grains is very important for extracting that extra bit of flavour and achieving a very nice clear wort. However, not everybody boils at 100C. Especially for pale lagers, temperatures of 90C – 95C are often employed. Your mileage may vary but it’s certainly worth a try. You may want to increase the boil time when using a lower temperature.
Now the hot grain should be gradually and carefully returned to the main mash in order to increase the temperature to the next step in the mash schedule. It is important to do this gradually under permanent stirring in order to avoid the enzymes being excessively denatured by the shock of the hot grain coming in.
I hope this sheds some light onto how a brewer has more influence on the outcome of the mash when using a decoction. How the grain is converted in that first decoction is most important. Think of it as doing 2 mashes and you are on your way! This also explains why a decoction mash is just so much longer than a step infusion or single infusion.
It’s worth it though. Even if you don’t think it contributes to the taste. By pulling the last (thin decoction) and boiling it until the proteins break, a very clear wort flows into the kettle and a lot of unpleasant by-products are already left in the sparge tun.