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Grainfather Blog - Week 170: Decoction Mashing - Part 2

By Sam Loader - Resident Brewer 18/10/2018 12:02 Comments

Decoction Mash

Grainfather decoction brew day

Time for the double decoction brew day of this Märzen style Fest beer, we’ll run through what I do when decoction mashing with the Grainfather.

Please note like with any brewing technique there are many different ideas and methods around how decoction mashing can an should be done the following is one method that is reasonably simple to carry out, and reasonably close to historical methods.

To do a Decoction mash on the Grainfather, you will need:

  • Grainfather
  • 2.6 gal (10 L) stockpot and some way to heat it, e.g. kitchen stove or gas burner
  • 1 quart (1 L) Pyrex glass measuring cup
  • 1 ladle
  • Thermometer

To do this decoction mash, we will be taking advantage of the Grainfather Brewing Community (brew.grainfather.com) recipe creator and the Connect Controller to hold a very stable mash temperature while we do the decoction. 

Recipe Märzen:

 Stats:

Volume 23L (5 Gal)

OG: 1.056

FG: 1.011

Est ABV: 5.9%

Boil time: 90mins

Mash time: 130mins

Mash Temps: 50, 65, 750C

IBU: 22

Mash water: 20.1L

Sparge water: 14.3L

 

 

Mash temp 0C

Mash Time mins

Decoction Boil Time mins

50

35

20

65

35

20

75

10

-

Program the mash time and temperatures into your recipe, do not worry about the decoction boil time yet

Fermentables

  • 4.0 kg (8.2 lb) Pilsner malt
  • 1.4 kg (3.09 lb) Munich Malt
  • Carahell or Carapills 0.3 kg (0.66 lb)
  • CaraMunich II 0.45 kg (0.99 lb)

Hops

  • 50.00 g Saaz Pellet Boil 60 mins
  • 20.00 g Saaz Pellet Boil 20 mins

 

Yeast

  • 2.0 packets Mangrove Jack's Bavarian Lager M76

Fermentation

  • Fermentation 12-14 days 100C
  • Diacytel rest two days 160C
  • Lager 5 weeks at 5-60C

 

Step One (First Decoction): 500C infusion

Fill and set up your Grainfather with water as per normal. When at 500C mash in as a normal brew day except do not use the top plate nor the lid.

Then using the ladle and 1 L jug, ladle 2.46 L of thick mash (the minimal amount of water transfer possible) into your stock pot and bring to the boil. By the time you have done this, there should be about 20mins left on your mash timer on the Grainfather. Use the remaining time as the decoction boil time. Stir the boiling decoction constantly so that it doesn’t burn to the bottom of your stock pot.

Once the first step of the mash has finished, add the boiled decoction back to the rest of the mash and stir evenly. The temperature of the mash will rapidly jump to the next mash step (650C)

 

Step two (Second Decoction): 650C

As soon as you are at 650C in the mash tun you can start taking the second decoction

Then using the ladle and 1 L jug, ladle 2.34 L of thick mash (the minimal amount of water transfer possible) into your stock pot and bring to the boil. By the time you have done this, there should be about 20 mins left on your mash timer on the Grainfather. Use the remaining time as the decoction boil time, boil times of 20-50 mins are fine. Stir the boiling decoction constantly so that it doesn’t burn to the bottom of your stock pot.

Once the second step of the mash has finished, add the boiled decoction back to the rest of the mash and stir evenly. The temperature of the mash will rapidly jump to the Mash out  (750C)

 

Mash Out : 750C

Because during the decoction you stir the grain bed very often and this allows the small grain matter to fall into the base of the boiler. This small grain matter can increase the chance of scorching. Therefore at the mashout step, I turn off the heat remove the grain basket and place this over in a separate bucket and empty the Grainfather into this bucket. Then if there is need ill give the Grainfather a little clean, then place the grain basket back into the sparge position and pour the entire lot of the mash water back through the grains before starting the sparge. By doing this, it allows the grain to reform a good filter bed, and the result is much less particulate matter into the boil, and therefore there is even less chance of scorching or tannin extraction from any grain matter in the boil. This should be able to be done before the end of the 10mins for the mash out.

 

The sparge, boil and cooling then occur in the typical Grainfather fashion and then ferment to your preference and that’s how to do a decoction mash with the Grainfather.

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