Double Decoction - Sound right???

I am trying to understand this double decoction process for an Oktoberfest I am brewing this weekend. I would like to use this double decoction schedule but want to make sure I understand it so I don't screw up.

1. Heat 22 Qt water to 139.6 F and add grains, stir, let rest 10 mins
2. Take out 7.83 Qt of grain and boil for 30 min, then add back to mash to raise temp to 158º for 90 min
3. Take out 4.71 Qt of grain, boil for 30 min, add back to mash to raise temp to 168º for 10 min
4. Sparge with 3.4 gal water at 170º

Does all that seem right? Please let me know!

Not exactly. First, your first decoction should be "thick" (just enough liquid to surround the grain). Your second decoction should be thin.

Also, you need to rest your first decoction at 158°F for a little while before boiling. This decoction rest time and your decoction boil time can vary, but 30 min. is a bit long for boiling the decoction IMO. I usually rest the decoction at 158°F for 10 minutes, then boil for 5 min. But you could boil a little longer if you like to get more melanoidins.

OK, I guess I really don't know how to schedule this out then. I thought that you started at a low temp (below 158), then your first decoction would be to raise the temp of the entire mash to about 158 where it would rest.
What SHOULD a typical decoction schedule look like? (Laid out in noob terms)

Watch the videos here. That should give you a good idea.

Yeah I watched the videos, and it still is unclear.

What Mensch is referring to I have highlighted in the attached schedule. You want to rest the decoction at a high sacc temp (160ish) to get the most conversion possible.

Just to be clear, the dashed lines in the schedule represent the temp of the decoctions.

Also, make your decoctions a little bigger than software says you need, by about 20%. When you return the decoction, only add back what you need to hit your target then let the remaining decoction cool to that temp outside the main mash.

Resting the decoction at a temperature that is optimal for alpha amylase is done for several reasons. α-amylase can break down starches that are too complex for β-amylase to break down. So, by resting in the 158°F range, you're breaking these complex starches down to less complex starches and dextrins. Then, after boiling the decoction, you add this back to the main mash where the β-amylase and α-enzymes are preserved and they break them down further into dextrins and simpler sugars.

If you skipped by this rest in the decoction and went straight to boiling it, you wouldn't reduce these complex starches and they would end up in your final beer, reducing your efficiency, fermentability, and would leave the beer hazy. In the mash-out decoction, you've already achieved the conversion you want, so you can skip the decoction rest and go straight to boiling it.

OK, I think I am understanding this a little better now, but why wouldn't you decoct the entire mash so you could convert all of the grains? Why only a portion?

Does this schedule look better?
1. Heat 22 Qt water to 144º, add grains (11.5 lbs) and stir well to achieve 130-135º
2. Decoct 7.5-8 Qt thick grains, raise temp to 158º, rest 10 min, then boil for 30 min
3. Add decoction slowly back to MLT to get 153º without going over, rest for 60 min
4. Decoct 4.5-5 Qt wort, boil for 10 min, add back to MLT and rest 10 min
5. Mash out and sparge with 3.4 gal 170º water, or enough to collect 6.5 gal wort

macabra11 said:

OK, I think I am understanding this a little better now, but why wouldn't you decoct the entire mash so you could convert all of the grains? Why only a portion?

Click to expand...

The original purpose of a decoction was to raise the temperature of the mash through the various rests required for the undermodified malt that was used. Today, the malts homebrewers get are very well modified and multiple rests or decoctions are not required. They're mainly done to achieve the maltiness produced by the melanoidins that are created in boiling the decoction.

However, decocting a whole mash wouldn't be decocting. If you just rested the whole mash at the 158°F range, your resulting wort would be overly dextrinous (low fermentability). If you subsequently boiled the whole mash, you would extract tannins and other polyphenols that would give the beer a bad flavor.