Never add Carbonate unless your pH is too low (Acidic). This will only happen if you are brewing an extremely dark stout or similar colour beer!
Carbonate is the enemy, by carbonate I mean Bicarbonate (H2CO3) Carbonate as is in Washing Soda (Na2CO3), or even Hydroxyl like (NaOH) Caustic Soda. These all raise the pH of the mash we nearly always want to lower the pH.
It makes no sense to raise the pH, then try and lower it by using salts.
All the salt additions lower the pH by making Calcium (Ca) ions available, these combine with Phosphate from the malt and form insoluble Calcium Phosphate and leave spare Hydrogen ions in solution. By definition the pH is a count of the number of H+ Ions in solution.
Add to this that there is a limited amount of Phosphate in malt there is only so much pH lowering effect you can get by adding salts, once the available Phosphate is used up the salts wont lower the pH any more, then you need acid.
Note that Magnesium Phosphate, what you would get if you added Epsom Salts rather than Calcium Sulphate (Gypsum), is less effective there are three forms of Magnesium Phosphate the insoluble form uses twice as much Phosphate to get the same pH lowering effect as you get from one Calcium ion. There is an old saying,
anything Magnesium can do Calcium can do better, Its pretty true. Yeast needs some Magnesium, but there is generally enough available in the malt. So to my mind its a pretty pointless addition. Basically enough Magnesium Sulphate to be really useful is getting up towards the doses people use as a laxative, the last thing we want is beer that gives us the *****.
Sulphate makes hops more pronounced and harsher, don't forget the harsher part. Too much can get pretty much.
Chloride makes beer mellower, smoother, rounder, more palate full and malty... Too much will start to taste salty.
A balance of the two lets you make beer that you like the taste of.
I use Calcium Lactate if I want more Calcium than is provided by the amount I get when I have added the amount of Sulphate and Chloride I want, then use Lactic Acid (others work to notably Phosphoric) to adjust the pH to where I want it.
Have a read of how pH affects mashing
Braukaiser covers it really well, in fact the whole section called Brewing Science is well worth a read. The following is worth a look too.
Just take the Carbonate away until your pH meter says you need to raise the pH (probably never).
Mark
