Hoping Martin will chime in here...
I will be brewing a fairly standard RIS soon, but, due to the limitations of my system (Grainfather), I'll have to do a reiterated mash, but I'm wondering how best to treat my water for each step? I start with 100% RO water. My plan is this - keen to hear thoughts/suggestions (and yes, I know I could just add extract and do one mash, but I want to give this a go!):
1. Mash exactly half the grain bill as per usual at 149°F for 60mins, treating the water as per usual for that volume (in this case it will be 4.6 gallons) but leave out the Gypsum and CaCl2 additions as I'll be needing to raise the RA of the mash.
2. Sparge the first mash with pure RO water to reach full pre-boil volume.
3. Pump off wort into a separate vessel that I'll use for the 2nd sparge, until I'm left with 4.6 gallons of wort in the mash tun for the 2nd mash.
4. Add the 2nd half of the grain bill, mash at 149 for 120mins.
5. Sparge using the wort collected in step 3 above.
6. Add Gypsum and CaCl2 additions and boil as usual.