It’s no secret that brewing dark beers like stout with soft water is challenging but it’s one I want to overcome. The trick is getting the mash pH into an optimal range by increasing the bicarbonate level with brewing salts to counter the effect dark malts have in lowering the mash pH value. The basic two options to raise the bicarbonate level are sodium bicarbonate (baking soda) and calcium carbonate. I tend to avoid the former because my water has enough sodium from the water softener therefore I use calcium carbonate. The challenge with calcium carbonate is that while it increases the bicarbonate levels to raise pH it also increases the level of calcium slightly which lowers pH so essentially it’s two steps forward one step back. What I end up doing is adding calcium carbonate until I reach the upper recommended limit of calcium (150 ppm) and stop there, wherever the bicarbonate level should lie.
During my last batch however I took a different approach.
I found the mash pH low as expected after dough-in. Recalling I have never heard of any adverse effects when using too much calcium compared to other minerals (and I’m not saying none exist), I threw caution to the wind and started pouring calcium carbonate into the mash. At around 12 grams I had raised the mash pH to 5.4 (room temperature) – right within the optimal range.
One bit of evidence that this did in fact have a positive effect is that I overshot my target original gravity by 6 points without changing any other of my typical brewing practices. Normally I formulate recipes with a brewhouse efficiency of 68%. Recalculating with the actual original gravity reveals an efficiency of 77%. This is the highest mash efficiency I have experienced of any batch.
It appears I need to stock up on calcium carbonate.