Low Ph on RO water

Today I went and got 14 gallons of RO water. I had two 7 gallon containers when I got home I checked the Ph and it was about 5, which I thought was pretty low. I had previously had star san in them which has a low Ph but I poured it all out, and You always hear dont fear the foam so I was not worried to much about it. Tomorrow I am going to take a clean gallon jug and get some more and check to see if the residual star san in the containers is what brought the PH down or if the RO water really is that low. Does anyone use RO water and know what the Ph usually runs, I guess it may differ from area to area not sure though? I went ahead and brewed the mash ph looked fine?

RO water has negligible mineral content, and therefore little buffering capacity. So the pH is largely irrelevant. What is relevant is the pH of your mash. It will acidify your water, and without any buffering power, it could drop too low for effective enzyme activity. So generally, it is a bad idea to brew with only RO water unless you are doing extract.

It is a great idea to use RO water for your StarSan. You don't WANT any of those minerals in that case, because they may degrade the highly acidic solution, which is what is responsible for the lethal power of Star San solution.

Since I'm a chemist and I've actually worked for a company that made RO units, I feel I should comment even though I'm not an AG brewer yet. In the lab we always get low pH on distilled and deionized water samples. It means very little when you're dealing with ultra pure water. In fact water that pure can take in atmospheric carbon dioxide quite readily, which will acidify it slightly until you get some solids in there.

Now what it means to brewing, well you got me. But you'll be heating it, which should mean it degasses. However ultrapure hot water is quite aggressive, so here's a question: is extracting tannins an issue with this type of water? I wouldn't think so, because the sugar would go in faster making it not ultrapure anymore. But I'm curious.

I usually take 12 gallons of RO and and mix it with 2 gallons of filtered tap...It usually gets me in the ball park.....I just thought that the Ph of the RO was unusually low. I dont think extracting tannins is an issue unless your mash ph or sparge water ph is too high, or you hit your mash with water above 170F. If your making say a Light american lager....You dont hardley need to add anything to RO except acid........But if your making an IPA....you add quite a bit.....Thats what the guys in the brew club do anyway, they usually get lots of medals so I believe it to be true.

To a chemist like myself a pH of 5 is a high pH. A low pH would be 12......please apply appropriately what pH really is.

Boy I've had too much Yerba Mate and Guarana this morning.


Off my high horse now......

As a homebrewer, I see it differantly. Its a tall horse not a high horse.

rhag1128 said:

To a chemist like myself a pH of 5 is a high pH. A low pH would be 12......please apply appropriately what pH really is.

Boy I've had too much Yerba Mate and Guarana this morning.


Off my high horse now......

Click to expand...

I think the use of the term "high pH" here means high ph value, which is a commonly used interpretation of the term, even for chemists or other physical scientists.

Your use of the term suggests that pH is synonymous with acidity, which seems like a less common use to me.

rhag1128 said:

To a chemist like myself a pH of 5 is a high pH. A low pH would be 12......please apply appropriately what pH really is.

Click to expand...

pH is a measure of the hydrogen ion concentration of a solution, or:

pH = -log[H+], where H+ is expressed in mols per litre.

drayman86 said:

pH is a measure of the hydrogen ion concentration of a solution, or:

pH = -log[H+], where H+ is expressed in mols per litre.

Click to expand...

Oh ****, no your didn't (snap snap snap in a Z-motion)

edit: You mean Moles, not mols I think

I also think he meant Hydronium Ion, (H+)

I would like to attempt an in depth explanation just for anyone who might be interested: In pure distilled water the hydrogen ions [H+] and the hydroxide molecules [HO-] are in complete balance. When water spontaneously dissociates (which it tends to do in predictable quantities) it breaks down from H2O into a H+ and a OH-.
In one liter of distilled water you will find about .0000001 (10 to the negative 7) or [10^(-7)] moles of hydrogen ions.
Math Warning!!!!! pH = -log[H+] When you see log[x] it is assumed that you mean log base 10 of the variable [x] unless it says otherwise (such as log3[x]). We are concerned with log base 10 which would look like this log10[x] (The 10 should be a subscript, but I don't know to enter that). So log10[10] is asking you to find the power that you raise the number 10 to that would give you 10. The answer is of course 1 (10 to the 1 power is 10). Therefore, with the above formula, substituting in the number of H+ ions which is 10^(-7) we get this expression -log10[10^(-7)]. And according to the logarithm properties the power or exponent can be brought down in front of the log which gives -(-7)log10[10]. The negatives cancel and we are left with 7(log10[10]) And we already figured out that log10[10] equals 1 so 7 times 1 = 7 which is the pH of distilled water. Because of this logarithmic property the pH value of 6 has TEN times more hydrogen ions (more acidic) than a sample with a pH of 7 and a pH of 8 (more basic) has only a TENTH of the number of hydrogen ions that distilled water does. OK, that really got out of control, sorry.