Double mashing Imperial Stout - mineral water calculations...

[bionut]

I am a BIAB brewer and i want to brew an Imperial Stout. Until now i always mashed all the grains (for imperial stouts that is) in as much water as i could and i would sparge the grain bag to get the right preboil volume. It worked good enough, but the efficiency was low. So now i want to brew another Imperial Stout but with the double mashing technique.
Having in mind that i use 100% Reverse Osmosis water and bru'n'water for my mineral additions, how should i divide the grain bill and calculate the minerals addition for reaching the target water profile and mash pH?

This is the recipe, i may change some things or leave it as it is... don't know yet:

8.00 kg Pale Malt (2 Row) Bel (5.9 EBC) Grain 5 59.9 % 5.22 L
2.00 kg Oats, Flaked (2.0 EBC) Grain 6 15.0 % 1.30 L
1.00 kg Cara-Pils/Dextrine (3.9 EBC) Grain 7 7.5 % 0.65 L
0.50 kg Brown Malt (128.1 EBC) Grain 8 3.7 % 0.33 L
0.50 kg Caramunich Malt (110.3 EBC) Grain 9 3.7 % 0.33 L
0.50 kg Carared (39.4 EBC) Grain 10 3.7 % 0.33 L
0.30 kg Caraaroma (256.1 EBC) Grain 11 2.2 % 0.20 L
0.20 kg Chocolate Malt (886.5 EBC) Grain 12 1.5 % 0.13 L
0.20 kg Roasted Barley (591.0 EBC) Grain 13 1.5 % 0.13 L
0.15 kg Black (Patent) Malt (985.0 EBC) Grain 14 1.1 % 0.10 L
35.00 g Centennial [10.00 %] - Boil 60.0 min Hop 15 27.5 IBUs -
35.00 g Centennial [10.00 %] - Boil 30.0 min Hop 16 23.5 IBUs -
1.0 pkg English Ale (White Labs #WLP002) [35.49 ml] Yeast 17 - -

 

[Beer666]

When I have done them I only worry about the ph for the first mash. The second mash seemed to take care of itself as I got very high efficiency. I used a 2 to 2 chloride/sulphate ratio and sparged with untreated RO.

 

[RM-MN]

It worked good enough, but the efficiency was low

How low? Mash efficiency depends on the milling of the grain. How finely did your grain get milled? Lauter efficiency depends on how well you sparge. Pour over or dunk sparge? Once or twice or more? Brewhouse efficiency depends on how much of the wort gets to the fermenter. Do you try to leave hops and break material behind?

 

[bionut]

Well, lower than my usual 5-6% abv beers, so clearly it have something to do with the grist weight. Also, i pour over sparge, while mixing in the grains with a big spoon.

 

[BrewnWKopperKat]

So now i want to brew another Imperial Stout but with the double mashing technique.

What have you read/watched on double mashing?

 

[bionut]

Do you know a thread/video i could read/watch that can answer my question about RO water mineral and pH calculations? Clearly i don't have a way to write here all i read about this thing, but i didn't found an answer.
My plan is to split the base malt in two halfs, and add the caramel malts in the first mash (with the minerals from bru'n'water for that grist), and in the second mash add the second half of the base malt with the roasted/black malts, with the remaining minerals calculated in bru'n'water with the full grist.
Altough it may work like Beer666 said.

 

[BrewnWKopperKat]

Altough it may work like Beer666 said.

My experiences with double mashes are similar to what @Beer666 said in #2.

 

[jerrylotto]

I did the same thing recently. First I did a half batch in a single mash - got great efficiency for that (around 85%). Total water volume used was 3.3 gal mash and 2.5 gal sparge ending up with about 3.5 gal cooled wort after the boil.

Then I did a full batch about a month later as a double. I mixed the grains well so the bill was the same in each step. First mash was identical to the half batch but I used 3.3 gal of the wort with the second half of the grain for the second mash, sparging again with 2.5 gal water. Efficiency overall was just about 80% and I ended up with 5.5 gal after the boil.

In all cases, the water I used for both mash and sparge was treated,, pH adjusted RO.

Both batches tasted great (I changed the kettle hops a little between the two recipes so I can't compare them side by side). One observation on your recipe - I would double the yeast.

 

[thehaze]

I did some double mashes in the past months. I use a Grainfather and I literally did the same mash twice. I don't sparge, as it kind of defeats the purpose of double mashing. Every mash is done with new, treated water - If you leave the wort from the first mash to soak the second round of grains, that's an reiterated mash and it does not help raise your volume, but only gravity. It's useful for when your equipment does not allow you to brew high gravity beers, without going down on volume. I could easily do a 12-13% beer in my Grainfather, but I would probably end up with 2.5 gallons of beer, and I am not keen on doing that.

 

[BrewnWKopperKat]

Grainfather

In many discussions (and magazine articles) "double mash" and "reiterative mash" are the same process. Are some of the "all-in-one" systems also using "double mash" to describe mashing half the grain bill in two completely separate mashes?

 

[Bobo1898]

I've had good success doing a double mash when I've evenly split up my grain while shopping for the very reason I can manage the mineral additions.

By doing this, my grain bill is the same for both mashes. And then in Bru n' water, I was able to change the sparge water volume as I saw fit when it came time to add additions in whichever step I was doing next.

To hit my target gravity, I still needed a little more water than usual and a longer boil time---2 hours or so.

 

[thehaze]

In many discussions (and magazine articles) "double mash" and "reiterative mash" are the same process. Are some of the "all-in-one" systems also using "double mash" to describe mashing half the grain bill in two completely separate mashes?

OK, I didn't know that a double mash is the same as a reiterated one. I was under the impression that reiterated mash means you have a grain bill, which you split in two or three, etc. The first mash of the reiterated mash, is made soaking your grains in treated, brewing water for a specific number of minutes/hours. Once done, you sparge to get the volume needed to mash in again - grain absorbtion, etc. Then you remove the grains, leave the wort in your mash tun/kettle and then put in the rest of the grains ( if grain bill split in two ). That means, you mash in the remaining grains using the wort extracted from the first mash. Then, at the end of your second mash - assuming you split the grain bill in two - you sparge to get pre-boil volume. Lastly, you boil. This is a reiterated mash.

I haven't used a reiterated mash - I didn't want to sparge, as part of an experiment, which turned out quite well ( which I then repeated a few times ). What I did, was split my grain bill in two - every mash was performed using freshly treated, brewing water. There was no sparge water used in the process. The wort from the two mashes was combined in the kettle and boiled. The spent grains could've been sparged to get second runnings for a small, table beer, but didn't go through with it.

I am inclined to say that maybe it is incorrect to call what I did, a double mash, but it's certainly not the same as a reiterated mash. My feeling, and with my limited experience as a homebrewer, tell me that the same beer brewed using these two technics will differ in terms of mouthfeel and body. I never used reiterated mash, so I cannot say if the results would be better, worse or on par with a no-sparge, double mash. But knowing how combined first runnings from 2-3 mashes look, taste and smell like, and knowing how sparge actually ( and visually ) dilutes and thins out the beer, I am not sure they would compare in terms of mouthfeel and body. I specifically enumerated the two attributes/factors, as these are the ones I am interested in, besides high gravity. Although high OG is a desirable result of these processes, high OG can be obtained easier with simple sugar/DME/LME additions - this again will negatively impact body, thinning it out.

 

[BrewnWKopperKat]

Thanks for the detailed explanation @thehaze. I don't know what the "official" definition of "double mash" - for the moment, knowing it may have two different definitions in this topic is helpful.

 

[thehaze]

Thanks for the detailed explanation @thehaze. I don't know what the "official" definition of "double mash" - for the moment, knowing it may have two different definitions in this topic is helpful.

I am also unsure what the definition is. I am however happy with the results I got from mashing as described above. I will probably do a reiterated mash at some point, so I can test it out and see which I like best.