Adjusting water hardness and pH of a beer mash

I had the opportunity earlier this week to work at my brother-in-law Chris's microbrewery, and it was a blast.  The day before that we had stopped by and he showed me around.  It was amazing to me that they had started from nothing not too long ago (< 1 year), and now they had a row of fermenters, grain mill, and several other pieces of equipment whose names I don't know, but I know what they do from home-brewing experience.  What was exciting for me personally was that a lot of the technology and equipment was familiar to me from grad school!  I studied surface science: how Nickel metal can catalyze chemical reactions.  We used steel chambers under ulta-high vacuum, and so we had lots of pumping systems, cooling systems, pneumatic systems, and the chambers were connected to gases via steel lines.  All of this is present at the brewery as well other equipment.  Anyway, it was great to "see some old friends" as we used to say when we'd see a familiar piece of equipment in a different setting.

The main thing we worked on was investigating the pH (acidity) of the mash.  A general recommendation is that the pH of the mash should be in the range 5.1 to 5.4 but Chris had consistently been measuring it to be 5.7.  Not a huge problem, but in the quest for better beer it seemed like a good idea to figure out what was going on.  We started discussing on the way there.  The city water was reported as being pH 8, and Chris had a pH meter and had made measurements at various locations by sampling the water there and under various conditions.  We decided to do something similar, write it all down, and then try a mini-mash and see if by adding some salts and/or phosphoric acid we get the pH into 5.1 - 5.4 range.

Edit:  pH is important because it affects the enzyme activity during the mash, and the yeast activity during the fermentation:
http://byo.com/fruit-beer/item/1493-the-power-of-ph
http://www.howtobrew.com/section3/chapter15-2.html


We made the measurements with digital pH meter, and I timed the measurements so that we could be confident that the reading had stabilized (typically 2-4 minutes).  We also found that stirring the water was important; it made the reading stabilize much faster (it was recommended in the manual for the meter to stir the sample).

Here is what we did:

• measured back water read ph 8.10
• Ran calibration on pH meter using standard solution, when finished it read 7.01 as expected
• Reran back water:  ph 7.43
• the calibration changed the reading by 0.67
• Run front water:  7.80
• this is the water as close as possible to where it comes from the city - close the reported value of pH 8
• Run brew house water: 6.58
• hot liquor tank water, heated to ~75 C, then allowed to cooled to ~45 C:  7.90
• we measured it at ~45 C because the highest operating temperature that the meter is rated for is 50 C
• we wondered if temperature was affecting the readings, so we measured the calibration solution at ~35 C:  6.90
• expect 6.98, so this is only a minor discrepancy
• Hot liquor tank water, cold:  7.75
• Brew house water, 2nd run:  6.64
• consistent with initial run
• Cold liquor tank water:  7.75

We decided to go ahead and try the mash, but we would add calcium sulphate (CaSO4) and see if it would adjust the pH. Brewers use CaSO4 to adjust the water hardness.  

Edit:  The calcium ion concentration, like pH, affects enzyme activity and yeast activity:
http://www.howtobrew.com/section3/chapter15-1.html

The recommended water hardness is "200 ppm" or 200 parts per million, which is a concentration of 200 mg per Liter (mg / L) of calcium carbonate (CaCO3).  The city water report stated that the hardness was 54 ppm, so we needed to get our concentration up by ~150 ppm = 150 mg / L.  Our test mash would be done in 10 L of water. We estimated the amount of CaSO4 we needed using:

150 mg / L * 10 L = 1500 mg = 1.5 g

The smallest unit on the scale we had was 1 g, so I ended up weighing out 24 g, and then dividing that in half several times until I was at what might have been roughly in the same ballpark as 1.5 g.  We put the mash together (10 L hot water, 4.5 kg grain, 1.5 g CaSO4), mixed it up, let it sit a bit, and then took a sample.  We let the sample cool, and when it was at ~45 C we measured the pH:  5.4!  Success!

I should have corrected for the relative molecular weights CaSO4 (136 g/mol) and CaCO3 (100 g/mol)  We should have used:

1.5 g CaCO3 * (136 g/mol CaSO4) / (100 g/mol CaCO3) = 2 g

But this is well within the error of the scale I used to measure out the CaSO4.

Another thought that occurred to me is that a pH range of 5.1 to 5.4 is not necessarily right, but if you want to use others' guidance, you need to follow their instructions - in this case, that includes adding CaSO4 as a water hardening agent.

Why does it work?  There might be some kind of base (weak) present in the water (pH of 8, so yeah) and the CaSO4 reacts to neutralize it via the reaction:

Ca(2+) + 2OH-   --->  Ca(OH)2

Here are the pKa's of the relevant compounds: 

CaSO4 ~10.4

CaSO4 . 2H2O ~ 7.3

CaCO3 ~ 9

I'm not sure if we have the dihydrate or the anhydrous form of CaSO4, I suspect the dihydrate because we're not doing any special handling to keep water out.  So I probably should have used a MW of 172 g/mol, which would have further adjusted the amount of CaSO4 to 2.6 g