Something I've always wondered that would help me with mashes for very dark beers:
Is it okay for me to add nothing but Baking Soda (Sodium Bicarbonate) to the mash to raise the mash pH in a very dark beer?
A bicarbonate (HCO3-) ion contributes half as much alkalinity as a carbonate (CO3--) ion. Thus 100 mg/L CaCO3 yields 100 mg/L alkalinity as CaCO3 (no surprise there). 100 mg calcium carbonate contains 2 "milliequivalents" of proton absorbing carbonate ion. 100 mg of sodium bicarbonate, OTOH, contains only 1.2 meq proton absorbing bicarbonate ion and thus 100 mg/L sodium bicarbonate increases alkalinity by but 60 mg/L as CaCO3. Thus you need more of it.
Does the mash actually need Calcium, or can I add my Calcium Sulfate, Calcium Chloride, etc. after the mash and in the boil kettle?
No as is indicated by the fact that some of the worlds finest beers (Bohemian Pilsners, Munich Helles...) are brewed with water that is low to very low in calcium. If you are concerned that mash pH will be too low you certainly do not need it for pH reduction. Calcium has other benefits to enzymes (including those active during mashing), trub formation, yeast metabolism all the way down to scavenging oxalate from the finished beer so calcium is beneficial but it can be added in the kettle as the chloride. Except in rare circumstances don't want to add it as the carbonate because it will raise pH. The rare circumstances are where you have somehow attained a lower pH than desired.[/quote]
...Estimated SRM: 41.6...To get a pH of 5.3, I'd need a Residual Alkalinity of 295+.
Unlikely unless you are adding so much roast malt that the beer would be, to my taste anyway, undrinkable. To give you some perspective, I use 10% roast barley in my Irish Stout. My water has an RA of about 60 and the mash goes to pH 5.5. The color of the beer, which really has very little to do with this, comes out to between 60 and 80 SRM. In laboratory experiments with distilled water (RA 2.5) and Maris Otter ale malt it required 30 % roast barley to get a pH as low as 5.2.
However, I also need at least 50 ppm Calcium. And, I want 100 ppm Chloride and 50 ppm Sulfate. To get all of that and still maintain a pH of at least 5.3 during the mash, I'd need: 1.94g Epsom, 3.15g Calcium Chloride, 7.58g Baking Soda, 3.03g Undissolved Chalk.
If you added all that to 5 gal of distilled water you would, with 10-20% roast grains, most likely come up with a pH much higher than desired.
If I'm lucky and all I actually care about during the mash is pH and not the actual mineral content,
That really is where most of your concern should lie. In some beers the minerals are part of the taste profile and you want to take some care to get them into the right range at least but in most cases it is mash pH that should drive your mineral additions or lack thereof. I don't know what your water is like out of the tap but were I you I would make a test mash with the grist you intend to use and check the pH. It may be fine or, if your water is alkaline it may be higher than you want (in which case you would need to add calcium and/or acid) and it may be too low. In my experience the last is the least likely but it could happen if you use lots of really acid roast malts. In this case you can add some calcium carbonate to the mash until pH falls into the right range. Scale the addition up to full size, mash away and be sure to check pH in the mash tun. Adjust additions in future brews until you are hitting mash pH every time.