Ph of RO after exposure to air?

[agentbud]

I use RO water for my brewing. In my brewing software, I have my water profile for RO set at a starting Ph of 7 and adjust it accordingly for the mash. However, I just read an article that stated that RO water left out will have its Ph drop to around 5.5 within an hour of being exposed to air? I normally run my RO system hours before brewing so that I have enough water, so it is definitely sitting out exposed to air for a while.

Is it true that this will indeed cause the Ph of that water to drop to around 5.5?

 

[DBhomebrew]

Whether true or not, it matters not.

With RO, is all about alkalinity. The water's resistance to pH change. If exposure to air can shift the pH, just think of what the grist will do.

 

[VikeMan]

Is it true that this will indeed cause the Ph of that water to drop to around 5.5?

Somewhere around there. Maybe closer to 6. But it's a very "weak" 6-ish, because it took very little acid (in this case carbonic acid, from disolved CO2) to move the pH from 7 to 6-ish. Distilled (or good RO) water has very little buffering capacity.

What is it that you're concerned about?

 

[agentbud]

Somewhere around there. Maybe closer to 6. But it's a very "weak" 6-ish, because it took very little acid (in this case carbonic acid, from disolved CO2) to move the pH from 7 to 6-ish. Distilled (or good RO) water has very little buffering capacity.

What is it that you're concerned about?

Well, I'm sure it has to do with my lack of understanding of water pH, but in my mind I look at it this way. If I assume I am starting with a pH of 7, and I want my mash to be at a pH of around 5.2-5.3, I use the software calculations to add enough lactic acid in the mash water to bring it down to that 5.2-5.3 level. But if, in reality, my starting pH is already at 5.5 due to the air exposure but I am still adding the same amount of lactic acid (as if it were at 7), wouldn't that bring the actual pH down way lower than my 5.2-5.3 target?

 

[VikeMan]

Well, I'm sure it has to do with my lack of understanding of water pH, but in my mind I look at it this way. If I assume I am starting with a pH of 7, and I want my mash to be at a pH of around 5.2-5.3, I use the software calculations to add enough lactic acid in the mash water to bring it down to that 5.2-5.3 level. But if, in reality, my starting pH is already at 5.5 due to the air exposure but I am still adding the same amount of lactic acid (as if it were at 7), wouldn't that bring the actual pH down way lower than my 5.2-5.3 target?

For mash pH purposes, the pH of the water is basically irrelevant. The mash pH will depend on the alkalinity (buffering capacity) of the water, the amounts of calcium and magnesium in the water, the acid contributions and buffering capacities of the malts, and the impacts of anything else you add (like Lactic Acid) to the mash.

There's nothing to be gained by pre-reducing the pH of the water to 5.2/5.3. I'd recommend looking into one of the various mash pH calculators, several of which are free.

Also, you might want to take a look at this presentation, Intro to Brewing Water Treatment.
https://sonsofalchemy.org/wp-content/uploads/2019/01/Intro-to-Brewing-Water-Treatment.pdf

 

[Henbrew]

Well, I'm sure it has to do with my lack of understanding of water pH, but in my mind I look at it this way. If I assume I am starting with a pH of 7, and I want my mash to be at a pH of around 5.2-5.3, I use the software calculations to add enough lactic acid in the mash water to bring it down to that 5.2-5.3 level. But if, in reality, my starting pH is already at 5.5 due to the air exposure but I am still adding the same amount of lactic acid (as if it were at 7), wouldn't that bring the actual pH down way lower than my 5.2-5.3 target?

No, the only thing that's causing the water pH to change is dissolved CO2. Once you heat that water up the CO2 will dissolve out of solution very quickly.

If you use any brewing software/calculator and adjust the ph of distilled or RO water, the pH will barely change, if at all.

Here's an example from Brewersfriend, this water profile I'm using is based on RO water but is close enough to distilled so that's what I enter.

Here the pH is 7 and the mash pH is at the top.

Now I set the pH to 5 and this is what is shows.

No change.

 

[VikeMan]

No, the only thing that's causing the water pH to change is dissolved CO2. Once you heat that water up the CO2 will dissolve out of solution very quickly.

The reason that the dissolved CO2 doesn't matter is that there's not enough of it to make a difference. It's true that when the water is heated, some of the CO2 will escape, but again, it doesn't make a difference. The amount of CO2 that brings 5 gallons of distilled water down to a pH of 6 is equivalent to ~0.002 ml of 88% lactic acid. Add 0.002 ml lactic acid into any mash and see what it does (nothing).

 

[Henbrew]

The reason that the dissolved CO2 doesn't matter is that there's not enough of it to make a difference. It's true that when the water is heated, some of the CO2 will escape, but again, it doesn't make a difference. The amount of CO2 that brings 5 gallons of distilled water down to a pH of 6 is equivalent to ~0.002 ml of 88% lactic acid. Add 0.002 ml lactic acid into any mash and see what it does (nothing).

I agree completely, I was just discussing the CO2 part of things.

 

[agentbud]

Thank y'all for the info. This helps a lot.

 

[Silver_Is_Money]

When something on the order of about 1/20 of a drop of 88% Lactic Acid is all that is required whereby to effectively duplicate the CO2 pH lowering phenomenon for 5 gallons of the most pure of water, the magnitude of the insignificance in this becomes apparent.

So when your software predicts that you should add 4 mL of 88% Lactic Acid, be sure to subtract 1/20 of a drop before you add the remainder of the 4 mL's of acid.

 

[Silver_Is_Money]

The entry indicating 6.5 in the chart above was likely a typo, as 5.6 seems well more appropriate.

 

[jtrainer]

To think some of us have pulled water from lakes and streams with a simple filter and brewed while camping. Even going as far to put hot rocks into the boil kettle and turned out great beer.

 

[Silver_Is_Money]

Water does have a major buffering component in the form of Alkalinity (most likely as Bicarbonate). Acidifying any Alkalinity bearing water to pH 5.4 reduces its initial Alkalinity level by right close to 90%.

 

[Silver_Is_Money]

Trivia:

Did you notice in the resistance/conductance chart that the inverse of Conductivity is Resistance?

The primary unit of resistance to electrical current flow is the OHM, and the same for freedom of electrical conductance is the MHO (which is OHM spelled backwards).

 

[Silver_Is_Money]

Water does have a major buffering component in the form of Alkalinity (most likely as Bicarbonate). Acidifying any Alkalinity bearing water to pH 5.4 reduces its initial Alkalinity level by right close to 90%.

Some may be shocked by this, as it means that water with 250 mg/L (ppm) Alkalinity still has ~25 mg/L Alkalinity when acidified to pH 5.4. But have no fear. The brew-mister scientists of yore (meaning before home brewing sprouted micro-brewing) had already determined that sparging with water at up to 50 mg/L Alkalinity will not harm your beer. This might be reassuring to those who occasionally brew with river water. Depending upon the river...

 

[CleanEmUpIves]

Often wondered what effect DI water (deionized) would have on a mash. Seems it would be the same as RO or distilled even if it could be used before exposure to air.

 

[day_trippr]

Distilled --> Deionized --> RO. But, in practice, interchangeable.
Put another way, I would not spend the money on a DI stage on top of my RO system which knocks out 4.25 gph @6~7 TDS.

And don't worry about product water pH. Even if it dives down to 5.8 or so, it's irrelevant...

Cheers!