[font=helvetica, arial, sans-serif]I'm planning a Big Stout and I going to have to split my grain bill and I'd really appreciate your help.[/font]

[font=helvetica, arial, sans-serif]Related BYO article :- [/font][font=helvetica, arial, sans-serif]https://byo.com/bock/item/1317-reiterat ... sive-brews[/font]

[font=helvetica, arial, sans-serif]My plan is to mash 1/2 then this will require 33 litres of water and remove the grain. Sparge to make up to initial volume (33 litres), and then mash the other 1/2 in the wort from the first 1/2..   Sparge again to get to the correct pre-boil volume.  [/font]
[font=helvetica, arial, sans-serif]Continue with processing in the usual way.[/font]
[font=helvetica, arial, sans-serif] [/font][font=helvetica, arial, sans-serif]But I don't know about water treatment.[/font][font=helvetica, arial, sans-serif] [/font]
[font=helvetica, arial, sans-serif]I'd very much like to get decent efficiency and for that I need the correct treatments.[/font]
[font=helvetica, arial, sans-serif]If I treat just the 1st mash then the treatment for the 2'nd 1/2 will be wrong so what  do I do?  [/font]
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[font=helvetica, arial, sans-serif]Thanks for your help.           aamcle[/font]
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BM users seem to double mash for gravity or volume and so far my research seems to suggest no additional treatment excepting one brewer who added a little Chalk to the second mash.
 I'll continue to think about the volumes and sparges.


aamcle

I'm making a huge stout far to big for my equipment, the reiterating method involves splitting the grain into two in my case aprox 5kg and 5kg and then mashing the first portion as normal but with out a mash out step.  The grain is lifted out of the kettle but the still active enzymes and the sugars from the first portion are in the wort in the kettle. 
This enzyme rich wort is used as the mash water for the second portion of grain. So in all there are two mashes done.
There is a Basic Brewing Radio Podcast about the procedure (year 2007) but it's not using BIAB, a similar double mash can be done with BM to get more volume or higher gravity.
In the research I've been done I have found no references to extra water treatment other than that one brewer who added some Calcium Carbonate which as you say is barely soluble.  So I not inclined to bother with additional treatment.
I'm still thinking about the best way to convert Reiterated Mashing to BIAB, so far my thought is to wash the grain from the first mash and use the resulting weak wort to wash out the grain from the second mash. 
I hope to get decent efficiency but I'll have some LME on standby.

aamcle

I'm using some grains that have been milled together or I would do just as you suggest


aamcle

I have a report and routinely test for Alkalinity prior to brewing.  My water supply is very hard, so hard that I can't use it for lagers even with additions  but with little in the way of treatment it makes good stout.  

ATB    aamcle