Calculating Sparge water in a Decoction Mash

So with my shiny new chest freezer I am going to take my first hack at a lager and I love Octoberfests so that shall be the one.

Since I have tons of free time and hate myself I am going to tackle a double decoction mash. So planning my beer with 10.5 lbs of grain out on an infusion schedule at my standard 1.25qt/lb it gives me 3.78 gal strike and 4.37 gal sparge water

However I know that you need a thiner dough in with a decoction mash So my plan is below I just can't figure out exactly how much sparge water I need once I hit mash out and I gather it would have to be at 170 as well?


Strike water 1.75 Qt/lb -> 18.375 Qts strike hold at 122 for 20mins

1st decoction (thick) -> Pull 1Qt per lb so -> 10.5 Qts of thick mash
Boil for 30mins

Add back to mash to hit 149, hold for 60 mins (if extra remains add cool water to even temp out at 149 and ad back to tun.

2nd Decoction (thin) -> Half of strike water, drain 9.2 qts of thin mash from tun and boil for 30 mins

Heat sparge water at this time ( Volume???)

Add the 2nd Decoction to the tun to mash out at 170

Then Sparge as usual

Also does a decoction mash change when you would add any water adjustments? Acids, Salts?

Let me see if I can simplify this for you.

A couple of pro brewers a long time ago explained that doing the decoction extends the malt profile of the beer. It can be done at any time during the mash process, but does not necessarily need to be used to raise temperature.

What I do is do my mash as usual, and get the mash mostly converted, if not completely converted. Then I do either one or two decoctions, the final one helps to or completely raises the temperature to mash out temp. The end result will be the same, and all the enzymes are left to do their thing undisturbed until they are no longer needed.

I mash on a stove top in a SS pot, so while decoction 1 is being done, I typically lose a few degrees in temperature, so it usually takes two anyway to get to mash out around 168F.

It does help to have some extra water in the mash, so if you have the space feel free. I have a sparge arm so I just sparge until I have enough in the brew kettle.

So essentially you don't worry about a protein rest or any of the non saccrification rest points? You're just looking to create melanoidins and get some maillard reactions going?

thegreatmaibockaddict said:

Let me see if I can simplify this for you.

A couple of pro brewers a long time ago explained that doing the decoction extends the malt profile of the beer. It can be done at any time during the mash process, but does not necessarily need to be used to raise temperature.

What I do is do my mash as usual, and get the mash mostly converted, if not completely converted. Then I do either one or two decoctions, the final one helps to or completely raises the temperature to mash out temp. The end result will be the same, and all the enzymes are left to do their thing undisturbed until they are no longer needed.

I mash on a stove top in a SS pot, so while decoction 1 is being done, I typically lose a few degrees in temperature, so it usually takes two anyway to get to mash out around 168F.

It does help to have some extra water in the mash, so if you have the space feel free. I have a sparge arm so I just sparge until I have enough in the brew kettle.

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Savage06 said:

Since I have tons of free time and hate myself I am going to tackle a double decoction mash. So planning my beer with 10.5 lbs of grain out on an infusion schedule at my standard 1.25qt/lb it gives me 3.78 gal strike and 4.37 gal sparge water

Click to expand...

This gives you a total water requirement of 8.15 gallons.

With the decoction you are starting with 4.59 gallons of water then I would think you would then need 8.15 - 4.59 = 3.56 gallons of sparge water.

Everything should be the same. Water - Grain Absorption = Starting Boil Volume.

I would have a little extra water on hand because even though the decoction boil will not be a vigorous boil you are still boiling the liquid for a total of 60 minutes so you will lose some volume. It is also good to have extra boiling water handy just in case adding the decoction back does not raise the temperature enough.

I recently did a BIAB 2 gallon triple decoction Maibock that is currently lagering.

I think this was the question you were asking.

Yes, Thank you sir. So like a 8 hour brewday?

Looking back at my brew log I started at 8:15am and finished at 2:15pm.

It does add a lot more time to your brew day. It is very cool though to see the decoction start to darken up as you are boiling it.

NTexBrewer said:

I would have a little extra water on hand because even though the decoction boil will not be a vigorous boil you are still boiling the liquid for a total of 60 minutes so you will lose some volume.

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I'd plan on losing up to a gallon to the decoction boil.

Nice explanation Dave!
Savage- if you want to look at a longer, more detailed explanation, check out Braukaiser's site. Kai has alot of info. on traditional german techniques.