Why does water harness lower the mash pH?

[frankvw]

In his latest edition of How to Brew, John Palmer writes (on page 338):

"Water hardness helps lower mash pH, and water alkalinity raises mash pH."

While I understand alkalinity and the way it makes water resist pH changes when mixed with acid (or malt), I am not sure how water hardness helps lower the mash pH.

I am not a water chemist and my few years of highschool chemistry are a mere memory, so explanations which throw a bunch of anions and cations and titration protocols at me are a little bit more than my poor little brain can handle.

Could anyone explain this to me in terms that someone with only a basic understanding of chemistry can understand? All attempts in this general direction would be most appreciated!

Tnx!

 

[bitteritdown]

Hardness comes from metal ions like Ca, Mg, Na, Fe which react with phosphates in the mash to release protons, thus counteracting the pH raising effect of alkalinity.

Alkalinity (the measure of resistance to change in pH) comes from carbonates/bicarbonates/hydroxide.

http://braukaiser.com/blog/blog/2011/02/01/calcium-and-magnesiums-effect-on-mash-ph/
http://braukaiser.com/documents/effect_of_water_and_grist_on_mash_pH.pdf
http://www.wetnewf.org/pdfs/Brewing_articles/Cerevesia/Final_galley

 

[mabrungard]

Hardness is due to divalent metal ions in the water. While that does mean that iron and manganese are technically hardness contributors, they won't be present in significant quantity in water that's fit to drink. That means that calcium and magnesium are the only functional hardness ions in drinking water.

They react with Phytin from the malt and hydrogen protons are released as a product of the reaction. There is a huge amount of phytin in wort, but the water typically only has limited amounts of calcium and magnesium. So, its the calcium and magnesium content of the water that drives the proton production and subsequent wort pH depression.

 

[frankvw]

Thanks, everyone! I think I'm starting to get it now.

So does that mean that the difference between the terms Total Alkalinity and Residual Alkalinity is that the former applies to industrial and household effects (e.g. limescale) whereas the latter applies to the effect on mash pH?

 

[mabrungard]

Yes, RA is a brewing only term. It can't be totally relied upon for managing mashing pH though.

 

[frankvw]

Thank you! Now it all makes sense.

 

[frankvw]

Hardness is due to divalent metal ions in the water. While that does mean that iron and manganese are technically hardness contributors, they won't be present in significant quantity in water that's fit to drink. That means that calcium and magnesium are the only functional hardness ions in drinking water.

On a related note, if my (somewhat limited) water report only specifies hardness as CaCo3, is there a way to determine the amount of carbonate and bicarbonate ions from this? I do understand that 40% of CaCO3 is Calcium and 60% is carbonate, but beyond that I'm not sure what assumptions I can get away with.

 

[mabrungard]

Both alkalinity and hardness are commonly reported in terms of 'as CaCO3'. So its easy to confuse those components. However, they are quite different.

You can convert alkalinity 'as CaCO3' into carbonate or bicarbonate concentrations. You may also convert hardness 'as CaCO3' into calcium or magnesium concentration. However, that hardness 'as CaCO3' has nothing to do with alkalinity, carbonate, or bicarbonate content.

 

[ajdelange]

\
"Water hardness helps lower mash pH,
Could anyone explain this to me in terms that someone with only a basic understanding of chemistry can understand? All attempts in this general direction would be most appreciated!

Malt releases lots of monobasic phosphate ions, H2(PO4)-. These react with calcium ions to form hydroxyl apatite:

10Ca++ + 6H2(PO4)- + 2H2O ---> Ca10(P04)6(OH)2 + 14H+

in which the phosphate ions (and 2 water molecules) release the protons (H+). While most of the released protons are absorbed by bases in the malt enough are left over to bring about a small downward change in mash pH. The reaction takes place to a pretty large extent because hydroxyl apatite is very insoluble (your teeth are made of it) so that it immediately precipitates and is removed from the mash. An important chemical (and economic....) principle called LeChatelier's principle tells is that if a reactant is removed from the right side of the equation the reaction will proceed to the right in order to try to re balance equilibrium.

 

[ajdelange]

On a related note, if my (somewhat limited) water report only specifies hardness as CaCo3, is there a way to determine the amount of carbonate and bicarbonate ions from this?

Yes, from the alkalinity if it is given if not you can still wag it. Hardness as calcium carbonate has nothing to do with calcium, carbonate, bicarbonate or calcium carbonate. It is an archaic (but solidly entrenched) way of expressing the equivalence of cations (usually calcium, magnesium or their sum). When you see 'as CaCO3' simply divide by 50 to obtain the equivalence of the cation(s) in question. If you see "Total Hardness 100 ppm as CaCO3" that tells you that the equivalence of calcium ions plus that of magnesium ions is 2 mEq/L. If you see "Calcium Hardness 100 ppm as CaCO3" that tells you that the equivalence of calcium ions is 2 mEq/L and that the concentration of calcium ions is 2*20 = 40 mg/L. If you see "Total Hardness 150 ppm as CaCO3, calcium hardness 50 ppm as CaCO3" that tells you that the equivalence of calcium ions plus that of magnesium ions is 3 mEq/L and that of calcium 2 so that the magnesium hardness is 1 mEq/L (12.15 mg/L).

If alkalinity and pH are given you determine bicarbonate and carbonate content from those but you seldom need to do that it the brewing application - the alkalinity is generally the only thing of concern as required acid additions for mash pH control depend only on it (though you may need to also know the waters's pH if it is high). If the alkalinity is not given you can guess at it by taking the total hardness (ppm_as_CaCO3/50) and adding the sodium concentration divided by 23 to that. If potassium, iron etc are present their concentrations should also be divided by their equivalent weights and added to the sum. This is the total cation charge. Now add up the charges (ignore negative sign) on all the anions you know about (chloride, sulfate, nitrate) and subtract that sum from the cation sum. The difference is an estimate of the alkalinity (in mEq/L so multiply by 50 if you are using a program that want as CaCO3).

 

[frankvw]

that hardness 'as CaCO3' has nothing to do with alkalinity, carbonate, or bicarbonate content.

I was afraid of that. I have a water report that only specifies Ca, Mg, Na, Cl, SO4 and "Hardness as CaCO3" (and pH but that's a different beast). Does that mean I'm missing some important information (CO3 and HCO3 ion levels) that I cannot possibly work out from what I have?

 

[mabrungard]

I was afraid of that. I have a water report that only specifies Ca, Mg, Na, Cl, SO4 and "Hardness as CaCO3" (and pH but that's a different beast). Does that mean I'm missing some important information (CO3 and HCO3 ion levels) that I cannot possibly work out from what I have?

That is correct, you are missing one of the most important factors for brewing: alkalinity or its associated ions. If those are all the information provided, you'll need to obtain an alkalinity test kit intended for aquarium use and determine your water's approximate level.

 

[Miraculix]

What about ajdelanges post?

 

[ajdelange]

People seldom carefully read posts to the point that I sometimes wonder why I bother but yes, my post does tell how to get a pretty good estimate of alkalinity from what OP has in his report. pH does not come into the alkalinity calculation using this method. If he wants to know HCO3- and CO3-- then he will need pH but he doesn't really need to know those until he goes to do a mash pH calculation from the alkalinity and then only if the pH is high.

This does not mean it is not a good idea to get the alkalinity test kit but while awaiting its delivery he can at least go ahead and get an idea as to what his alkalinity is.

 

[Rhaop]

What about ajdelanges post?

When Aj posts I think of a rocket scientist that answers questions for people who waited in line 5 hours just to ask how to build a better paper airplane /shrug

Not to discount any of the other great members on here but that’s next level stuff, good read as usual even if a lot of the math and data is way over my head

 

[Lefou]

For some reason, Palmer's writing style on homebrewing never led me to follow much of his advice or buy any of his books. There are other prominent homebrewers around who present the same info in different styles or perspectives - and for that very reason, I think that's why I'd rather read a book by Chris Colby instead.

 

[frankvw]

What about ajdelanges post?

That's where I started. Unfortunately it did not tell me exactly what I needed to know (at least as far as I understood it) which was if total hardness as CaCO3 can be used as an indication of carbonate ion levels, so I thought I would just ask.

 

[frankvw]

Yes, from the alkalinity if it is given if not you can still wag it.

OK. Wagging it is what I'm interested at the moment. I need to improve my water to brew a better beer, because all this water chemistry is driving me to drink!

When you see 'as CaCO3' simply divide by 50 to obtain the equivalence of the cation(s) in question. If you see "Total Hardness 100 ppm as CaCO3" that tells you that the equivalence of calcium ions plus that of magnesium ions is 2 mEq/L.

This is where I'm starting to loose track of it. Sorry to ask but could you give me a simple calculation example? Let's say my water data is as follows:

• Chloride, mg/l as Cl: 30
• Sulphate, mg/l as SO4: 35
• Calcium, mg/l as Ca: 55
• Magnesium, mg/l as Mg: 34
• Sodium, mg/l as Na: 15
• Hardness, mg/l as CaCO3: 164
• pH:7.6

That's it. That's all I have. Now how do I work out my carbonate ion levels? Assuming, of course, that I'm understanding you correctly at all and this can indeed be guesstimate on the basis of what I have. When you write that:

If the alkalinity is not given you can guess at it by taking the total hardness (ppm_as_CaCO3/50) and adding the sodium concentration divided by 23 to that.

I could take that to mean that my alkalinity would be the total hardness plus sodium/23, i.e. 164 + (15/23) = 164.65 but that doesn't seem right at all, which suggests that I have no clue what I'm doing.

Sorry to be a pain, but I've only had three years of very basic chemistry about 35 years ago, and juggling the molar valences of cations (or whatever) is not something I am familiar with. Maybe there is no way to do this without diving into it to the point of obtaining a degree chemistry, but from what you write I understand that there may be a way to at least make a best guess at carbonate ion levels and alkalinity that someone without your background could work out by simply plugging the numbers into a calculation.

Thanks for your help so far, by the way. I may not be able to understand it all but I do appreciate it!

 

[ajdelange]

Sorry to ask but could you give me a simple calculation example? Let's say my water data is as follows:

We start by tabulating the equivalent weights (atomic or molecular weight divided by charge, the sign of which will be ignored later) of the ions

• Chloride, mg/l as Cl: 30 atomic weight 35.45, charge -1, equivalent weight 35.45
  
• Sulphate, mg/l as SO4: 35 molecular weight 96 charge, -2 equivalent weight 48

The total charge from an ion is its concentration divided by its equivalent weight. Thus the total reported anion (negative) charge is 30/35.45 + 35/48 = 1.57543 mEq/L.

Now we do the same for the cations

• Calcium, mg/l as Ca: 55 atomic weight 40, charge +2, equivalent weight 20
  
• Magnesium, mg/l as Mg: 34 atomic weight 24.30, charge +2, equivalent weight 12.15
  
• Sodium, mg/l as Na: 15 atomic weight 23, charge +1, equivalent weight 23

Thus the total (positive) cation charge is 55/20 + 34/12.15 + 15/23 = 6.20053 mEq/L

There must, therefore, be 6.20053 - 1.57543 = 4.62513 mEq/L unreported anion charges as the positive and negative charges must cancel. We assume that they are hydroxyl, carbonate and bicarbonate. In doing an alkalinity titration the OH- ions are converted to water and the bicarbonate and carbonate to CO2. In any case we can guess that your alkalinity is numerically approximately equal to this difference i.e. 4.62 mEq/L. Multiplying by 50 gives the alkalinity as 231 ppm as CaCO3.

• Hardness, mg/l as CaCO3: 164
• pH:7.6

That's it. That's all I have. Now how do I work out my carbonate ion levels?

You really only need to know the alkalinity. To calculate the bicarbonate and carbonate requires some math that is in a sticky at the top of this forum. Given that the pH is 7.6 that labor probably isn't worth it as you can assume that there is no carbonate (in fact there is a little) and that the hydroxyl is unappreciable. Then the bicarbonate is simply 61 times the alkalinity i.e. 61* 4.62.

 

[frankvw]

We start by tabulating the equivalent weights [...]

Thank you, sir! I'm going to have to sit down for this with a cup of extra strong coffee, but the method is clear enough so I should be able to work it out now.

Much appreciated!