Does RO sparge water need to be acidified?

In a previous post Primo water was cited with these parameters:

pH - 7.3
Total Dissolved Solids (TDS) Est, ppm - 37
Electrical Conductivity, mmho/cm - 0.06
Cations / Anions, me/L - 0.5 / 0.5

Sodium, Na - 2
Potassium, K - < 1
Calcium, Ca - 6
Magnesium, Mg - < 1
Total Hardness, CaCO3 - 19
Nitrate, NO3-N - 0.2 (SAFE)
Sulfate, SO4-S - 1
Chloride, Cl - 10
Carbonate, CO3 - < 1
Bicarbonate, HCO3 - 6
Total Alkalinity, CaCO3 - 5

"<" - Not Detected / Below Detection Limit

Would this water need to be acidified before using for batch sparging? If so, what would be the appropriate amount of lactic acid (88%) to use?

No. There is practically no proton-sucking bicarbonate in it.

If the brewer were relying on pH to assess the suitability of their sparging water, it would take extremely little acid to drop the pH of typical RO water to the typical pH range between 5 and 6.

So practically, acidification is not needed or required.

OK - I'm bewildered. I'm aware of the mantra that says "Sparge water has to have a pH less than 6 or tannin extraction may occur". This water has pH of 7.3 - yet somehow because of the minimal amount of bicarbonate there's no reason to acidify. Is that because the grist itself will lower the pH below 6?

jmf143 said:

OK - I'm bewildered. I'm aware of the mantra that says "Sparge water has to have a pH less than 6 or tannin extraction may occur". This water has pH of 7.3 - yet somehow because of the minimal amount of bicarbonate there's no reason to acidify. Is that because the grist itself will lower the pH below 6?

Click to expand...

This has more to do with the water's ability to hold on to that pH than the actual pH itself.

Using this tool: http://www.brewersfriend.com/mash-chemistry-and-brewing-water-calculator/ try this (keep the default volumes):

enter an alkalinity of 10 ppm as CaCO3 and a pH of 10. Then open the "Sparge Water Acidification" tab and choose Hydrochloric acid. Click update calculations and you'll see that 0.2 ml HCl are needed to bring the pH of the 4 gal of sparge water to a pH of 5.4

Now enter alkalinity of 100 ppm as CaCO3 in the source water tab and a pH of 7.

After clicking update calculations you see that 2.26 ml HCl are needed to bring the same amount of water to a pH of 5.4.

Despite the higher pH of the first water its lower alkalinity means that it takes less acid to move that pH. The same happens during sparging where the acid is supplied by the mash. If the water has low alkalinity it will not be able to pull up the pH into the danger zone for excessive tannin extraction regardless of the actual water pH.

Kai

jmf143 said:

OK - I'm bewildered. I'm aware of the mantra that says "Sparge water has to have a pH less than 6 or tannin extraction may occur". This water has pH of 7.3 - yet somehow because of the minimal amount of bicarbonate there's no reason to acidify. Is that because the grist itself will lower the pH below 6?

Click to expand...

pH is not what you need to control in sparging water, its alkalinity. pH is just an indirect indicator of what the alkalinity is. The problem is that the pH and alkalinity are NOT directly proportional or keyed to one another. If you have really low alkalinity water like RO, then a pH of 7 is fine. That water's ability to consume (neutralize) the acidity of the mash and raise the mash pH is very low.

Contrast that with a very high alkalinity water that you have to neutralize with acid. Then the target pH might need to be 5 in order to reduce alkalinity to a low level. If you neutralized that water to only 5.5, there might still be significant alkalinity that could affect the pH of the finished wort.

But as AJ says, its hard to imagine adding two liquids together with 5.5 pH's and not ending up with a 5.5 pH. So I'm not sure that the alkalinity argument holds up when you are bringing the pH of the sparging water to an already desirable wort pH. There could still be some of issue with the remaining carbonic acid and its buffering later in the brewing process. Total conjecture on my part...

Ever think about what the 'p' in pH stands for. Lots of people will tell you it's 'potential' (it isn't really it's just a letter Sorensen used to designate hydrogen ion (and q was the letter he used for hydoxyl). But it could be because pH is a measure of the potential of something to donate protons just as the voltage on a battery is a measure of its potential to push electric current. A capacitor is really a better analogy but if you aren't familiar with electronics a battery is probably easier to understand. There are 2 volt batteries that are used in hearing aids and 2 volt batteries that are used to start diesel trucks. Both the same voltage (potential) but one can deliver a lot more current. It's the same with pH. It matters what the pH (potential) is because protons flow across potentials just as current does but a hearing aid size (low alkalinity) water cannot absorb as many protons as a truck battery size (high alkalinity) water can.

The reason that a capacitor is a better example is that if you have two caps charged to different voltages and connect them together current will flow until both are at the same voltage. If one capacitor is tiny only very little current will flow from a larger capacitor to it in order to charge it to the same voltage as the larger cap and, as the larger cap looses very little charge, its voltage won't drop much. If, OTOH, the second capacitor has large capacitance relative to the first a lot of current will flow and as the large capacitor now loses a larger proportion of its charge its voltage will drop appreciably.

pH:Voltage
proton flow: electron flow
Alkalinity:capacitance

Remember that alkalinity is better called 'buffering capacity'

Here is a question while the topic is open. I just installed an RO system in my house the other day and my pH readings on the water are 5.4... I was expecting something closer to 7. Does 5.4 sound right or is there something wrong with the installation?

Everything is cool. RO water has little buffering capacity (alkalinity). It is like a small capacitor. If you put any charge at all in it its pH will change quite a bit. There is a bit of CO2 in the air. It is quite soluble in water and when it dissolves it forms carbonic acid which, as the name suggests is a proton donor. The tiny amount in the air and the tiny amount of that which dissolves and the tiny fraction of that which actually emits protons is nevertheless sufficient to lower the pH of the water into the 5's or 6's.

mabrungard said:

So I'm not sure that the alkalinity argument holds up when you are bringing the pH of the sparging water to an already desirable wort pH.

Click to expand...

Remember that in measuring alkalinity we take a water sample to a pH of 4.5 whereas in brewing we only bring it to 5.5 or so. If I have a water 1L sample with a millimole of carbo at pH 8.3 (98% of that will be as bicarbonate) and then acidify to 4.5 (as I would do to measure the alkalinity) then 0.983 mEq of acid would be required to shift the bicarbonate (and another little bit, 0.03 mmol would be required to shift the water) so we'd call the alkalinity 1.01 mEq/L (50.5 ppm as CaCO3). If we shifted that same water to pH 5.5 it would take but 0.880 mEq/L (plus 0.003) for an alkalinity of 0.883 or 44.15 ppm as CaCO3. That water still has alkalinity as you would have to add 50.5 - 44.15 = 6.35 ppm as CaCO3 extra acid to reach alkalinity end point. But as far as having to add acid to neutralize the alkalinity of this water for proper mash pH establishment: you don't. You've already done that as long as you want 5.5 for the mash pH. If you want 5.4, for example, then you have to neutralize more bicarbonate but not the whole 6.35 ppm's worth only 1 ppm's worth as that's how much acid it takes to shift a mmol of carbo from 5.5 - 5.4.

I think a lot of people may be doing calculations based on the assumption that if you have alkalinity of 50 you need to neutralize all of it to get to mash pH. That would be true if alkalinity were measured to mash pH but it isn't. It's measured to about 1 pH lower. Thus you need to neutralize less than 100% of the alkalinity (~88% in this example).

ajdelange said:

I think a lot of people may be doing calculations based on the assumption that if you have alkalinity of 50 you need to neutralize all of it to get to mash pH.

Click to expand...

I think that might be done for the simplicity of it. While i think the exact approach is more correct and should be implemented in water calculators it is easy to argue that the difference of 12% is in the noise of all the other factors that determine pH in mash and sparge.

Kai

Yes but it changes with pH. My well water runs pH 6.4 usually and has alkalinity of 80. If I want to bring that to pH 5.5, to use the same example, I need 1.24 mEq/L of acid which, compared to the 1.6 mEq/L alkalinity is 77.5% for 22.5% error. I think that amount is OK for ROM mental calculations but 22.5 out of 100 is only 13 dB signal to noise ratio. Not so impressive.

PhelanKA7 said:

Here is a question while the topic is open. I just installed an RO system in my house the other day and my pH readings on the water are 5.4... I was expecting something closer to 7. Does 5.4 sound right or is there something wrong with the installation?

Click to expand...

Its OK. Gases will permeate the membrane very easily. The primary gas in water is CO2. So you end up with a lot of CO2 in the product water of RO systems. We often send the product water through air stripping towers to help get that excess CO2 out of the water so that the pH isn't crazy as you've observed.

mabrungard said:

Its OK. Gases will permeate the membrane very easily. The primary gas in water is CO2. So you end up with a lot of CO2 in the product water of RO systems. We often send the product water through air stripping towers to help get that excess CO2 out of the water so that the pH isn't crazy as you've observed.

Click to expand...

ajdelange said:

Everything is cool. RO water has little buffering capacity (alkalinity). It is like a small capacitor. If you put any charge at all in it its pH will change quite a bit. There is a bit of CO2 in the air. It is quite soluble in water and when it dissolves it forms carbonic acid which, as the name suggests is a proton donor. The tiny amount in the air and the tiny amount of that which dissolves and the tiny fraction of that which actually emits protons is nevertheless sufficient to lower the pH of the water into the 5's or 6's.

Click to expand...

That is interesting stuff. Thanks guys.

So when you say "put charge in it" do you mean the action of pumping the water from the holding tank? So the water in the tank would likely be a higher pH before it comes out the spigot? Or is this occurring within the membrane itself? I'm just asking out of curiosity. I can brew with pH 5.4 water just fine.

No. That phrase was drawn from the analogy with the capacitor. In chemistry terms I am saying that it takes very few protons, i.e. very little dissolved CO2 to shift the pH of the water to these lower pH's.

Once the water is exposed to air it will immediately pick up CO2 and become acidified. Or, if the water comes from a well in a region with nominal rainfall that water will contain dissolved carbonic at a higher concentration that water that is in equilibrium with the air. I have no idea what the rejection for carbonic acid molecules might be but I suppose it is less that 100% so some of the CO2 in the water could be from the source. In any event it will eventually equilibrate with the air especially if it is accumulated in an atmospheric tank. I also vaguely recall reading that hydrogen ions are rejected less than hydroxyl ions so that there is some decrease in pH from that effect (if I'm remembering that right).