Mash pH is important. There have probably been a bazillion gallons of beer brewed with the brewer not knowing the pH of the mash. However, as brewing science advanced, it became clear that malts contain a great number of enzymes that work best in different temperature and pH ranges. For example β-amylase works best in the pH 5.0 to 5.6 range while α-amylase works best at a higher pH (5.1 to 5.9). That’s why when brewers begin to monitor and control pH they get better efficiency. They’ve optimized one of the conditions for the enzyme to convert starch to sugar. The process happens with or without our intervention. All we do as brewers is set up certain conditions in an attempt to render certain results.
Calcium in the mash is important. Again, a bazillion gallons of beer have been brewed without adding calcium to the mash. But again, science tells us some enzymes have co-factors, or substances that help them work more efficiently. Calcium is an important co-factor for the amylase enzymes, and also helps protect α-amylase at normal mashing temperatures. Plus, adding calcium to the mash reacts with phosphates in the grain husks to release phytic acid, which slightly lowers the mash pH naturally. Add 1 tsp of CaCl or gypsum to the mash tun for every 5 gal treated for this co-factor effect.
Some of the calcium will be trapped in the mash. In Session Beers Jennifer Tulley says only about 40% of the calcium added to the mash carries over to the kettle. Therefore kettle additions may also be warranted depending on the beer style being created. Additional CaCl and/or gypsum as well as all other salts can be added at any stage in the brewing process from mash tun to glass. I use the Water Profile Tool in BeerSmith to calculate the effects of my additions.