Assumed pH of RO water in Bru'n Water?

[fat_astronaut]

Does anyone know what the assumed pH of RO water is in Bru'n water? Is the only way to change it is to input the assumed tds yourself as your own profile where you can choose your pH?

 

[mabrungard]

RO water pH has virtually no effect on the resulting mash pH. We are talking about altering mashing pH by a hundredth when the RO pH changes by a whole unit.

The most important thing is the alkalinity of the water. In the case of good RO water, that alkalinity should be very low.

 

[j1n]

RO water should be a neutral PH of 7. if you measure it though it will be off since you cant read RO water PH correctly.

 

[ajdelange]

DI (absolutely pure) water has, at 25°C, a pH of 7 (at 20 °C it's 7.085). Pure water exposed to air for even a few minutes will pick of CO2 from it and, at 20 °C, if exposed long enough to be at equilibrium with the air will have a pH of around 5.5. In an RO system the water is not pure. Even a small amount of alkalinity (from imperfectly rejected bicarbonate) will result in a higher pH. In the middle 6's might be considered typical.

pH is difficult to measure in low ionic strength solutions as very pure water is a pretty good insulator. Where such measurements are to be made an ion strength adjustor can be added to both buffer and sample. One can usually get a pretty good reading on RO water because there is, between the break-through ions and the dissolved carbon dioxide, a high enough ionic strength.

In any brewing water the pH is of secondary importance. It is alkalinity that primarily determines what happens in the mash tun. DO water is no different. Its pH is especially insignificant as pH info is used in conjunction with the alkalinity to determine electrical charge on carbonate and bicarbonate ions and RO water has few of either of these.

In a spreadsheet that asks for complete liquor info I use 7 for the pH, and 0 carbo (or 2.5 alkalinity to alkalinity end point 4.3) to describe RO water. Note that I use 7 for the pH even though I do most of my calculations at 20 °C. This doesn't make appreciable difference in results.

 

[KeninMN]

I'm guessing that since RO water has very little buffering capacity its pH has no impact on mash pH, which will ultimately be determined by the grain bill...

 

[ajdelange]

That's correct.

 

[fat_astronaut]

I just wanted to check, last time I tested the pH of my RO, it was 5.5. I have a meter now, and I intend to test it, but you say it won't matter? I plugged things in in Bru'n water, and my mash acidification read as 5.4, although my bicarbonate is lower than the suggested amount for the profile, (black balanced).

My report is posted here, if anyone can take a look and tell me if it looks good: http://www.docdroid.net/htla/porter-choc-hazelnut.pdf.html

 

[ajdelange]

No, it won't. Water is only one source of alkalinity in a mash and as RO water has none its effect on pH is largely nullified unless you add a lot of calcium to it. The positive alkalinities (proton deficits WRT mash pH) of base malts and low colored specialtymalts are offset by the acidities (proton surfeits WRT mash pH) of high colored malts. If these don't balance at the desired mash pH protons must either be added by the use of external acid (or more dark malt) or absorbed by the use of base, more light malt, or removing some dark malt. A calculator or spreadsheet needs to know in some detail the deficit/surfeit of the actual malts you are using. None of them do as the labor involved in getting that data is extensive. Therefore they must use approximations based on things like color or a reduced set of measurements on many malts or a detailed set of measurements on a few. They do, in many cases, a pretty good job of estimating mash pH but it is only an estimate. It is far better to control mash pH by the use of a good pH meter. Making a test mash before brew day is a very good idea. If a spreadsheet says your mash pH is 5.4 but it turns out to be 5.2 in a test mash you need to add some base or remove some dark malt. Even though the spreadsheet was pretty far off it can be used to give you an idea as to how much extra base is needed or how much dark malt to remove. Make the adjustment in the spreadsheet to raise its estimate by 0.2 and make that same adjustment to the test mash. Part of the reason the spreadsheet didn't get the right answer in the first place is because it didn't model the buffering (rate of change of pH with change in the quantity of protons) properly but it should have it close enough to the correct value to compute small changes reasonably well.