My commercially bottled distilled water pH didn't measure 7; is that typical?

[youngdh]

I would think that distilled water which is void of minerals and bicarbonates should be pH 7. Does this mean my commercially bottled steam distilled and ozonated water is not void of minerals meaning I'm not starting with a clean slate? Here is background that got me to this point.

My last brew (2 months ago) my target mash pH calculated using Bru'n water was 5.4 selecting 100% distilled water for dilution water. My measured mash pH using my calibrated MW102 meter 25 min in to mash was 5.1! I'd assumed since I was starting with distilled water my base water pH was 7 and didn't bother measuring its pH prior to brewing. I went back and measured the pH of my base water and it measured 6.6!

I brewed again yesterday and measured my distilled water pH after meter calc and again it measured 6.6. I plugged this into both brewersfriend.com adv water calculater and Bru'n water. My target pH was 5.4 which I had brewersfriend calc 10% phos acid addition to hit target pH. I took mineral/acid additions from brewersfriend and plugged into Bru'n water. Bru'n water calculated a mash pH of 5.5 vs brewersfriend's 5.4. I chose to use brewersfriend's mineral/acid additions. My actual measured mash pH 25 min into mash was 5.5 and what Bru'n water predicted.

Bottom line is it's now apparent that the distilled water I'm using isn't a neutral pH of 7 and makes me wonder if it's mineral and hardness isn't zero either which means I've no idea what I'm starting with as a water profile :-(


Sent from my iPad using Home Brew

 

[youngdh]

After making my initial post I found AJ's explanation on inaccuracy of trying to measure RO/DO water pH here https://www.homebrewtalk.com/showthread.php?t=491684. There was also discussion in this post that the base water pH has little affect on target mash pH and it's mash water hardness that impacts mash pH the most.

I also failed to mention in original post that I used base water pH of 6.6 and all zeros for minerals in both brewersfriend.com calculator and Bru'n water to get my mineral and acid additions for my target pH where Bru'n water's calculated target pH of 5.5 and was my measured pH of my mash yesterday.


Sent from my iPad using Home Brew

 

[mabrungard]

The pH of distilled water should be well below 7 when it's exposed to the atmosphere. CO2 dissolves into the water, forming carbonic acid. Since there is no alkalinity in the distilled water to buffer pH change, the pH of distilled water can easily fall into the 5 range.

 

[ajdelange]

I would think that distilled water which is void of minerals and bicarbonates should be pH 7.

Actually it contains a wee bit of bicarbonate and hydrogen ions to balance their charge. If the partial pressure of carbon dioxide in the atmosphere is 0.0003 atm. then the pH should be around 5.65 and the water will contain about 0.13 mg/L bicarbonate ion, 0.73 mg/L carbonic acid and hydrated CO2 and have an alkalinity of about 0.13 ppm as CaCO3. If PaCO2 goes up to 0.0004 atm the pH drops to 5.59, the bicarbonate is increased to 0.15 mg/L and the alkalinity decreases to 0.11 ppm.