I am getting ready to try my first partial mash on a marzen/oktoberfest ale according to the recipe below, but I have a few questions about the water I am going to use for mashing.
First, I do not trust my tap water at all and I will be using Deer Park spring water bought at the grocery store. Its water profile is here. For the marzen, I assume I want a residual alkalinity mash pH of 5.7-5.8 since that's what the waters of Munich give. However, the values given on that page have a really wide range, and those give mash pHs of about 5.8-5.9.
So, first question is: is using this water a good idea for this recipe? Second is: should I just use the average values of calcium, magnesium, and bicarbonate levels when calculating residual alkalinity mash pH? Third: do I need more than one rest at 150-158F with the grains I am using?
Final Volume - 5 gal
Boil Volume - 2.5 gal
Boil Gravity - 1.056
---Added Near Flameout---
5.0lb Light DME (Grav: 0.045, Color: 4.5L)
0.4lb Crystal 80L (Grav:0.025 , Color: 80L)
1.0lb Munich (Grav:0.026, Color: 10L)
0.5lb 2-row Lager Malt (Grav: 0.028, Color: 1.5L)
28g Hallertauer (or Liberty) pellets (4% AA) -40min (11.35 IBUs)
28g Hallertauer (or Liberty) pellets (4% AA) -30min ( 9.94 IBUs)
Original Gravity = 1 + 0.045 * 5/5 + 0.025 * 0.5/5 + 0.026 * 1/5 + 0.028 * 0.5/5
Boil Gravity = 1 + 0.045 * 2/2.5 + 0.025 * 0.4/2.5 + 0.026 * 1/2.5 + 0.028 * 0.5/2.5
Color = 4.5 * 5/5 + 80*0.4/5 + 10*1/5 + 1.5*0.5/5
= 13.05 SRM
Bitterness = 11.35 + 9.94
= 21.29 IBUs
The boil will be the liquid extracted from mashing the specialty grains plus 2 pounds of the DME.