RO Sparge Water

I recently installed an RO system and I've been having trouble adjusting the pH of my sparge water.

First the pH meter (MW101) seems to be having a hard time reading the pH. I'll put the probe in and the pH takes forever to stop and settle on a number.

Then, I'll add some phosphoric acid a few drops at a time and the pH won't change much, getting to the low 6's. Then I'll add two more drops and the pH will fall off the cliff and drop to around 5 or less.

If it makes any difference, I've already added any salt additions before taking the readings.

What am I doing wrong and does it matter if the sparge water pH is that low?

RO water has no buffering so very minute acid additions can cause big swings. For my recipes, Bru 'n water usually recommends about 0.1ml of 25% phosphoric...doesn't take much at all.

You said you added your salts before taking your pH measurement.

But you didn't say WHAT you added or how much to what amount of water.

Just what the previous poster said, RO water has very little buffering capacity and if you didn't add any salts to increase the buffering, you will see drastic swings in pH.

BTW.. reading the pH of RO water is hard for most meters, I believe AJ's Sticky on calibration mentions why and the details

Just plain RO water, regardless of the actual pH, is fine due to not having any alkalinity. In fact, plain RO water is ideal for sparging.

You don't need to add any salts at all to it. But if you do, assuming it's gypsum or calcium chloride and not something that increases alkalinity like baking soda, that's fine.

Yooper said:

Just plain RO water, regardless of the actual pH, is fine due to not having any alkalinity. In fact, plain RO water is ideal for sparging.

You don't need to add any salts at all to it. But if you do, assuming it's gypsum or calcium chloride and not something that increases alkalinity like baking soda, that's fine.

Click to expand...

Oh Right, what yooper said, Duhhh... you DON"T want to add alkalinity to sparge water.

Measuring the pH of a very low ionic strength liquid is tough. RO water is getting pretty low on the ionic strength scale, so I'm not surprised with the difficulty. The response observed with the few drops of acid and the pH cliff are typical. With virtually no buffering, the pH will fall off the cliff after only a few drops.

As mentioned above, straight RO water needs no acidification for sparging water use. The alkalinity is already nice and low. Mashing water could still require some acidification for pale grists.

CyclingCraig said:

You said you added your salts before taking your pH measurement.

But you didn't say WHAT you added or how much to what amount of water.

Just what the previous poster said, RO water has very little buffering capacity and if you didn't add any salts to increase the buffering, you will see drastic swings in pH.

BTW.. reading the pH of RO water is hard for most meters, I believe AJ's Sticky on calibration mentions why and the details

Click to expand...

For 10.29 gallons of sparge water, 3.5g of gypsum, 4.1g of calcium chloride.

Calcium, sulfate and chloride were all right around 50 ppm per EZ Water.

If I add any alkalinity, that has only been in the mash, none in the sparge water.

Anyhow, as long as I'm only adding gypsum and calcium chloride to the water, I won't worry about the pH of my sparge water.

Or would it make more sense to add the salts I'm adding to the sparge water to the kettle instead and just sparge with straight RO water?

Thanks.

Spartan1979 said:

First the pH meter (MW101) seems to be having a hard time reading the pH. I'll put the probe in and the pH takes forever to stop and settle on a number.

Click to expand...

It could be that your meter's electrode is at the end of its life. Do the stability check at https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/ but let the electrode stabilize in 7 buffer then rinse, shake off and install in pH 4 buffer noting how long it takes to reach its reading near 4 and how stable that reading is.

Note that since you have added salts and since this is RO water the difficulties attendant on measurement of low ionic strength solutions should not be a problem here.

Spartan1979 said:

Then, I'll add some phosphoric acid a few drops at a time and the pH won't change much, getting to the low 6's. Then I'll add two more drops and the pH will fall off the cliff and drop to around 5 or less.

Click to expand...

This is normal behavior when there is bicarbonate based alkalinity so the question is as to whether there is any or not. If your feed water is quite alkaline, say 200, and your bicarbonate rejection only 90% (because your membrane is at end of life) then the alkalinity of the RO water will be 20. If you are treating a large volume of water with dilute acid (10% phosphoric) then what you see can be explained by the normal titration curve of bicarbonate. OTOH if you bicarbonate rejection is 99% or your feed water less alkaline then the RO water's alkalinity would be about 2 ppm and the normal titration curve wouldn't be a very good explanation.

Spartan1979 said:

What am I doing wrong and does it matter if the sparge water pH is that low?

Click to expand...

You may be trying to use a dying electrode or you may be doing nothing wrong as discussed. Does it matter if the pH is as low as 5? That depends on how alkaline the RO water was which determines how much total acid you added which has an effect on the buffering capacity of the treated water. If you are looking for kettle pH of 5.1 or 5.2 and sparge with water at pH 4.8 with some buffering capacity behind it you will pull down kettle pH. If you have acidified pure water to pH 4.8 it won't (because the buffering of that water, even as treated, will be so low).

AJ, I just replaced the electrode in the last month or so, so hopefully that's not the issue.

Out of curiosity, I had a Wards report done on the RO water and the report said "Total Alkalinity, CaCO3 3"

So. would it make more sense to add the salts I'm adding to the sparge water to the kettle instead and just sparge with straight RO water?

Spartan1979 said:

AJ, I just replaced the electrode in the last month or so, so hopefully that's not the issue.

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I'd do the stability check anyway. Electrodes can be finicky. Some people have gone through 3 or more cycles of replacement before getting a good one with various manufacturers.

Spartan1979 said:

Out of curiosity, I had a Wards report done on the RO water and the report said "Total Alkalinity, CaCO3 3"

Click to expand...

Then pH should drop dramatically when even the smallest amount of acid is added. One drop of 10% phosphoric acid should lower the pH of 5 gallons from 7 (assuming that's where it starts) to 6.68, a second drop to 6.45, a third to 6.29, and 4 and a half drops to pH 6.

Spartan1979 said:

So. would it make more sense to add the salts I'm adding to the sparge water to the kettle instead and just sparge with straight RO water?

Click to expand...

It shouldn't really matter as neither of the salts you are adding should have any effect on mash pH but a powder labeled 'calcium chloride' can contain some calcium hyrdoxide which does. You should still not see the nothing, nothing, drop off the cliff effect even if your calcium chloride contains some hydroxyl ion.

Spartan1979 said:

Or would it make more sense to add the salts I'm adding to the sparge water to the kettle instead and just sparge with straight RO water?
Thanks.

Click to expand...

A couple of years ago I started building brewing water from RO. As commonly recommended, I was adding salts to the mash water while sparging with straight RO. I do a lot of competitions and although I was happy with the results of the water treatment, my score sheets begin to suffer and a slight astringency was commonly mentioned as a fault. After confirming all my processes were in line with preventing astringency (mash pH, sparge temp, final running pH and gravity, etc) I came across a post by our beloved Martin over on the AHA Forum where he was speculating on why his tea tasted better when using tap water vs RO water: https://www.homebrewersassociation.org/forum/index.php?topic=14292.msg181715#msg181715. Although it was only speculation at that time, I decided to add some calcium (CaCl2) to my sparge water. Problem solved and back on top at the competitions. Recently, I came across this post on the Probrewer forum: http://discussions.probrewer.com/archive/index.php/t-40322.html I'll paste part of it in here as I would like to here some discussion on this subject.

From probrewer.com-
"The need to mineralize the sparging water is another issue all together. On the one hand, increasing the ionic content can increase the osmotic pressure on the plant husk cells and potentially reduce the tendency for tannins or silicates to migrate into the wort during the sparge. However when brewing with very low mineralization water such as used in typical lager brewing, then there may or may not be a reason to mineralize the sparging water. One technique may be to NOT mineralize the sparging water so that the brewer can add the entire mineral dose for the batch into the mash and enhance the precipitation of oxalate from the wort. The addition of the unmineralized sparging water results in a desirably low overall ion content in the kettle."

I would like to add that I brew Belgian Pales exclusively and perhaps these styles are susceptible to astringency.

trentm said:

Although it was only speculation at that time, I decided to add some calcium (CaCl2) to my sparge water. Problem solved and back on top at the competitions.

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The chloride ion often gets overlooked. The reason we put salt in so many foods isn't all for salty flavor. The sweetness and mouthfeel lent by chloride are an important part of it too.

trentm said:

Recently, I came across this post on the Probrewer forum: http://discussions.probrewer.com/archive/index.php/t-40322.html I'll paste part of it in here as I would like to here some discussion on this subject.

From probrewer.com-
"The need to mineralize the sparging water is another issue all together. On the one hand, increasing the ionic content can increase the osmotic pressure on the plant husk cells and potentially reduce the tendency for tannins or silicates to migrate into the wort during the sparge.

Click to expand...

Osmotic pressure refers to the solvent pressure difference and would depend on the concentrations of all particles inside the grain compared to all those without. The difference between the osmotic pressure of distilled water and of water with 300 mg/L sulfate and an calcium at 125 mg/L (12.5 mOsmole) is only 2.2 psi so I don't think this is going to make the difference between the grains bursting or not. But migration of tannins isn't going to depend on the osmotic pressure difference of the solvent. It is going to depend on the chemical potential differences of the tannins (osmotic pressure is caused by the chemical potential differences of the water). As there are, initially, no tannins in sparge water whatever its mineral content there is going to be a huge chemical potential difference between the inside of the husks and the water. How much transfers depends on the usual heat and pH variables more than on the mineral content of the water.

trentm said:

However when brewing with very low mineralization water such as used in typical lager brewing, then there may or may not be a reason to mineralize the sparging water. One technique may be to NOT mineralize the sparging water so that the brewer can add the entire mineral dose for the batch into the mash and enhance the precipitation of oxalate from the wort.

Click to expand...

As long as calcium is there when the oxalate is there it will precipitate. Carrying some calcium into the package is a benefit from this POV (unless you do not want to allow precipitation of anything in the bottle).

trentm said:

The addition of the unmineralized sparging water results in a desirably low overall ion content in the kettle."

Click to expand...

There are two tasks at hand here. The first is to get the mash pH correct (with further mineral/acid additions as required for proper kettle pH) and the second is to finish up with the desired ion content for flavor. Whether one wants low mineral content in the kettle/finished beer would depend on the beer he is brewing. If you mash with a bbl of water and sparge with another and put all your CaCl2 in the sparge water you will have all the chloride in the beer but no pH reduction in the mash from the calcium. If you put all of it into the mash water you will have all the chloride and obtain full pH reduction from the calcium. If you put half in the mash water and sparge with DI then you lose half the calcium's pH benefit and half the chloride's flavor benefit.