Split Mash RIS Procedure?

[bonecitybrewco]

Just wondering how everyone is doing split mashes. I am planning on doing the following -

Heat strike water to mash in temp
Mash with ~1/2 of grain bill while maintaining target mash pH via Bru'n water
Remove bag/squeeze, place into separate vessel and add sparge water/stir let sit for 15 mins.
Dump bag and add 2nd half of grains
Reheat 2nd runnings up to mash in temp and dough in, mash as scheduled
Remove/squeeze bag, place into 2nd vessel with 2nd runnings, stir and leave for 15 mins, stir again and dump grains.
Add "2nd runnings" to first runnings and proceed as per normal

Does this sound correct or am I missing something?

Target OG is 1.104 and I know getting that with straight mash/double batch sparge may be difficult even with accounted for efficiency loss. I am normally at 83% BH efficiency but haven't done this big of a beer and so calculated at 70%. Wondering if I should calculate lower or the same for this batch based on this procedure.

I do have a large enough vessel to do a full volume mash in the bag without a sparge but I imagine it would be horrible efficiency...

Any ideas/thoughts?

Thanks in advance!

 

[element533]

I believe another term for that is "sequential mash", according to BYO. I haven't tried that method, but your description sounds accurate. But you shouldn't need to do a sequential mash to hit 1.104 OG.

Here's my process: Single infusion mash for 60 min in 11 gal rectangular cooler with approx 26.75 lbs grain milled at 0.039 and 8.3 gal strike water for a 1.25 qt/lb mash thickness (maxes out the mash tun). Single batch sparge with 2.2 gal @ 190 F (still quite thick). Vigorous stirring at mash in, mash out, and sparge. This gets me about 7.25 gal of 1.076 into the kettle and a 90 min very hot boil (about 1.3 gal/hr boil-off) gets me to 5.5 gal of 1.103. (Kettle trub, yeast, transfer losses gets me down to about 3.85 gal in bottles.)

Since you are doing BIAB (which is effectively a no-sparge mash), you should already be able to exceed the gravity numbers I'm getting, but at a sacrifice of volume. Although it is expensive to discard the extract left behind in the grain, that is certainly an acceptable method for boosting the gravity. But it may be a challenge to lift that much wet grain, unless you have a lift mechanism.

That being said, I'm interested in trying the sequential mash technique. One question I have is what happens with the pH/chemistry on the second mash, since you are mashing in with wort instead of strike water.

Edit: Corrected pre- and post-boil volumes

 

[bonecitybrewco]

Just to clarify, I am mashing in a bag, not doing a no sparge. I would be using all sparge water to rinse both sets of grain, that's all. Essentially a sequential batch sparge as well.

Thanks for the info. I really appreciate it. I have the volume to mash/sparge this large a volume, I was mostly just concerned about that large of a disparity between mash and sparge volume and reasonably how much volume would be lost to the grains or the boil.

And yes, I am asking in the brew science forum about the pH of the 2nd mash considering....I am having a difficult time finding anyone who seemed overly concerned about that aspect, but me being as OCD as I am about the whole process, it would be nice to know what to expect. Hoping Martin has a good idea...

Again, thank you for the info and how you do your procedure.

 

[element533]

Makes sense.

Regarding lost volume...

Grain will absorb about 0.19 gal/lb of wort (after normalizing volume to 68 F). This is usually given as 0.12 gal/lb apparent absorption out of the strike water volume, but this lower figure does not account for the increase in volume of the wort from having sugar in it. So depending on how you're modeling your calculations, A) you would either expect the strike water volume minus 0.12 gal/lb absorption as your first runoff volume, or alternatively B) you would calculate the increased volume of your strike water with extract dissolved into it and subtract 0.19 gal/lb from that figure to get runoff volume. Of course those exact numbers will vary for different mash gravities. Grain absorption is the primary factor for lower efficiency in big beers (for batch sparge).

Sparge runoff volumes seem to come out at or above 100% of the sparge water volume. Typically my mash runoff is a little bit low and the sparge runoff is a little bit high, so it evens out. So I would just calculate expected absorption from the mash and then assume 0 absorption from the sparge (in both 1st and 2nd parts of the sequence).

I've also noticed that first runnings and last runnings of a single batch runoff can have different gravities. I think this is due to the grain becoming more "sticky" as the liquid level drops below the grain level, causing it to preferentially hold onto sweeter liquid towards the end of the lauter. A hot sparge (190 F) and vigorous stirring seems to loosen this up and gets that sugar back out into the kettle. I have absolutely no references to back that up though, so take it with a grain of salt.

Boil off rate depends on how much heat your burner produces and how wide your kettle is. I have a 10 gal Blichmann, about 22 in across, and a 50K BTU Bayou Classic, and when I'm cranking it full blast, I get about 1.3 gal/hr. That corresponds to a highly vigorous, volcano boil that is constantly erupting and roiling over itself. A lower boil, where the surface is constantly stirring and bubbles are gently burping up and folding back into themselves is about 1.0 gal/hr. I reserve the hotter boil for dark/high gravity beers (or when I miss my pre-boil gravity!)

Aside: I perform temperature correction on all my volume readings and assume a 0% "cooling loss", since contraction is not really loss, it's just a measurement artifact.

 

[bonecitybrewco]

So based on all of that, what did your mash and BH efficiency end up at using your method?

 

[element533]

I was wrong before with my pre-boil volume, it was 7.25 gal and 5.5 gal post-boil (updated the original post).

Here are my exact numbers (all volumes and gravities are temp corrected):

26.62 lb grain (milled at 0.039)
8.32 gal strike (1.25 qt/lb, single infusion, no mash out)
2.22 gal sparge 190 F
0.30 gal MLT dead space
7.24 gal pre-boil (0.11 gal/lb apparent absorption)
1.076 pre-boil OG
90 min boil
5.54 gal post-boil (1.13 gal/hr)
0.29 gal kettle trub loss
5.25 gal into fermenter
1.103 OG
3.85 gal into bottles (1.4 gal fermenter loss - TONS of yeast and trub, plus tertiary transfer, etc.)
1.025 FG

When calculating my efficiency, I account for moisture in the grain (~4%), which most calculators don't consider. I started doing that because I was diagnosing some efficiency issues in the past and realized that my conversion efficiency was consistently 95% when I accounted for moisture. I suppose it doesn't matter whether you do this or not as long as you are consistent. Here are both calculations:

Accounting for moisture:
Mash efficiency = 61.0%
BH efficiency = 60.0%

Ignoring moisture:
Mash efficiency = 58.8%
BH efficiency = 58.0%

I use Beer Smith 2.