The carbonate ion and acidification

[ldave]

I did pretty well in chemistry (no organic, though). I've been brewing in my current location for about 8 years now. With pretty good success. My municipal water report indicates 80 mg/L of Ca and 127 mg/L alkalinity. So, the alkalinity number explains why I have to acidify nearly every brew (with the exception of stout) with phosphoric acid (2.5 mol) to reach target mash pH= 5.4. I also acidify sparge water to pH=5.6.

I've recently been reading the Water book in the brewing elements series and playing with a brewing water calculator (brewers friend). I've observed something that I don't quite get.

When I bring up a 'balanced profile for water target' in a water calculator, say for an american amber ale, it'll give a target for effective carbonates in the range of, say, 100 ppm. Keep in mind, in this exercise, we are not trying to duplicate the water of some locale. We are looking for the 'ideal' brewing water for the style (in as much as that exists) as if we were going to build from scratch (RO water). Now, what I observe is that no matter what I add or take away, in terms of minerals, if I hit that effective carbonate concentration, I always have to acidify. And the calculator shows that when I acidify, it reduces the alkalinity, and, consequently the effective carbonate concentration reduces. Now, I realize that when you acidify, the actual carbonate concentration doesn't change. It's just a titration. You're adding acid to rebalance equalibrium to a different pH.

My fundamental question is this: why are we having all those effective carbonates in there to begin with if we have to nullify them (acidify) to reach the target pH=5.4. Are all these carbonates important somewhere in the brewing process (and for the life of me, I can't see where)? Except in the case of very darks like stouts, wouldn't it be better to not have the carbonates to begin with and then not need to acidify? Shouldn't the 'recommended effective carbonate level' be: just enough to balance the mash pH=5.4? And just experiment with a given recipe to find that point?

I suspect that the reason this thought experiment won't work has to do with buffering. In the boil. In the fermenter. But could someone with a firm understanding elighten me?

 

[h-bar]

The only purpose carbonate serves is as a buffer, if you are not starting out with RO water. In the water chemistry primer sticky in this forum, carbonate is not even recommended as an additive to RO water. You can brew good beer without it. In fact, I have an IIPA going right now that doesn't contain added carbonate. I simply added the prescribed amounts of calcium chloride and gypsum. The beer is tasting great so far.

 

[mchrispen]

Most of the reports include bicarbonate and carbonate really to help folks determine how to treat the water for their usage. It is simply reporting what is there, either from a municipal, agricultural or geologic perspective, and often they are snapshots in time and not representative of an overall mean.

For brewers, as h-bar says, it is an indicator of alkaline buffering which you know. You also must remember that we have no practical view into the breweries of that region - and they can either heavily treat (Lime, R/O, Ion Resin, Carbon Filtering, etc.) the source, or as was the case before those treatment technologies came along, boil the water and allow the bicarbonates to precipitate. It is good advice to focus on the alkalinity of your mash, driven largely by Calcium and Bicarbonate, and secondarily on Sulfates and Chlorides, and then perhaps Magnesium and Sodium to tweak.

To further your argument, building from R/O why add extra acid to counter the bicarbonate level artificially created? It doesn't make sense. I want to use the minimal amount of acid/sauermaltz/minerals to achieve the desired mash characteristics from R/O. Naturally occurring bicarbonate is useful to naturally buffer the acidity of dark roast and crystal malts for dark beer.

 

[ajdelange]

And the calculator shows that when I acidify, it reduces the alkalinity, and, consequently the effective carbonate concentration reduces. Now, I realize that when you acidify, the actual carbonate concentration doesn't change. It's just a titration. You're adding acid to rebalance equalibrium to a different pH.

The carbonate concentration does change and so does the bicarbonate (the one that is really important) and carbonic. When you add acid bicarbonate converts to carbonic:

HCO3- + H+ ---> H2CO3

See p66 in the book.

Now, what I observe is that no matter what I add or take away, in terms of minerals, if I hit that effective carbonate concentration, I always have to acidify.

Absolutely. If you add bicarbonate it causes alkalinity and that has to be taken out by converting the bicarbonate to carbonic.

My fundamental question is this: why are we having all those effective carbonates in there to begin with if we have to nullify them (acidify) to reach the target pH=5.4.

Good question and the answer is because the people who are advising you to add bicarbonate don't understand the chemistry as well as you do.

Are all these carbonates important somewhere in the brewing process (and for the life of me, I can't see where)? Except in the case of very darks like stouts, wouldn't it be better to not have the carbonates to begin with and then not need to acidify? Shouldn't the 'recommended effective carbonate level' be: just enough to balance the mash pH=5.4? And just experiment with a given recipe to find that point?

That's right. Carbonate and bicarbonate are not necessary unless you are adding something that provides extra protons (proton surfeit) such as dark malt and your base malts haven't the capacity (proton deficit) to soak them up at mash pH. In such a case you need extra proton deficit (alkalinity) and bicarbonate is a source of that.

I suspect that the reason this thought experiment won't work has to do with buffering. In the boil. In the fermenter. But could someone with a firm understanding elighten me?

It does have to do with buffering. Everything in the mash has an intrinsic pH i.e. the pH that you would get if you mix it with DI water. For bicarbonate salts that is 8.3. For most base malts it is 5.75 or so and for dark malts it is 5 or less. You have a desired mash pH, say 5.4. Anything with an intrinsic pH higher than that will have to have acid added to it to lower its pH to 5.4. These things (bicarbonate, base malt) have proton deficits. Anything with an intrinsic pH less than the desired mash pH emits protons, has a negative proton deficit (proton surfeit) and acts as an acid. To hit a particular mash pH the proton surfeits of all the things with low intrinsic pH must just balance the proton deficits of the things with high intrinsic pH.

 

[ldave]

O.K. So this is a valid direction. I'm comforted. The water calculator still shows an acid addition to be necessary to hit mash pH=5.4 without carbonates. But its pretty small. The mash DI is 5.655 or so (for this amber), so you could probably not acidify and do fine. I will, of course, acidify to hit my mark precisely.

The stout will always need some carbonates. Good use for a water calculater.

h-bar: Did you acidify at all with just gypsum and CaCl? And did you measure pH?

I see that just using gypsum and CaCl misses the Mg component and the Na component. All malt provides way more Mg than can ever be used, so that's not relevant. The calculator's Na component is just 25 ppm. I'm supposing then, that because h-bar's beer is fine without it, and mchrispen calls it a 'tweak', is just not very relevant either.

The question would still remain, however, about the buffering action. If boiling reduces in pH and so does fermentation, would these pH reductions be enhanced with very little buffering activity (no carbonates)? h-bar has an example on hand that says 'no'. The sticky mentioned also indicates no carbonates necessary. So, then, all malt mash provides all buffering necessary?

 

[ldave]

ajdelange: Now that's an informed reply.

The carbonate concentration does change and so does the bicarbonate (the one that is really important) and carbonic. When you add acid bicarbonate converts to carbonic:

HCO3- + H+ ---> H2CO3

See p66 in the book.

Oopsey, missed that, didn't I? So that makes sense. The mash converts carbonates to end products that take the carbonates out of the alkaline game, reducing pH. As the reaction is limited by the amount of Ca (and this must be the core reason for Ca inclusion), at endpoint, if pH>grist DI of 5.655 then you still have unwanted water carbonates and these are what is titrated against with an acid addition. In the case of no water carbonates present, to get from grist DI pH=5.655 to pH=5.4 the acid titration proceeds against alkalines (presumably carbonates, as well) present in the malt. The presence of these, then, provides the buffer capacity of the wort for subsequent boil and fermentation in the absence of water carbonates. Am I close?

 

[ajdelange]

The water calculator still shows an acid addition to be necessary to hit mash pH=5.4 without carbonates. But its pretty small. The mash DI is 5.655 or so (for this amber), so you could probably not acidify and do fine. I will, of course, acidify to hit my mark precisely.

Base malts are alkaline with respect to mash pH. Pure water is slightly (very slightly) alkaline WRT mash pH but most calculators ignore this.

The stout will always need some carbonates. Good use for a water calculater.

No. It depends on the grains. Many of us do not use any carbonate with stouts and find mash pH to be a bit high i.e. a bit of acid would be of benefit.

I see that just using gypsum and CaCl misses the Mg component and the Na component. All malt provides way more Mg than can ever be used, so that's not relevant. The calculator's Na component is just 25 ppm. I'm supposing then, that because h-bar's beer is fine without it, and mchrispen calls it a 'tweak', is just not very relevant either.

The proper ion profile for your beer is the profile that gives you the beer you want. Given that mash pH is under control you are free to season as you like with sodium, magnesium, chloride and/or sulfate. Trying to hit a profile based on someones idea as to what the water of a particular city is like is pretty much a thing of the past. Yes, some beers require water with generally described profiles but they are quite broad.

The question would still remain, however, about the buffering action. If boiling reduces in pH and so does fermentation, would these pH reductions be enhanced with very little buffering activity (no carbonates)?

Boiling only reduces pH if there is calcium and bicarbonate which can coalesce to drop out as calcium carbonate. If there is no temporary hardness (no bicarbonate present) boiling will not reduce pH so there is an example where little buffering is associated with no pH drop. It is only where acid is added or removed (base added) that the buffering capacity of the mash comes into play. The pH change due to an acid addition/reduction is simply the acid addition divided by the buffering. Look at page 96 (Fig. 22) in the water book and understand what it is telling you.

Fermentation pH is controlled by the yeast. They will crank out acid until the proton deficit of the wort WRT to their desired pH has been nullified. If the wort has high buffering capacity that means they have to work hard at doing that and may not make it quite where they want to go but by and large they will.

The sticky mentioned also indicates no carbonates necessary.

In most cases we are striving to overcome the buffering (proton deficit) of the malt and acid in some form is required. In fewer cases the proton surfeits of the dark malts exceed the sum of the proton deficits of the base malts and the water and some additional base is needed.

So, then, all malt mash provides all buffering necessary?

In most cases malt exhibits higher proton deficit at desired mash pH than is tolerable and we must add acid to overcome that. See p 92 in the book.

 

[mchrispen]

The water calculator still shows an acid addition to be necessary to hit mash pH=5.4 without carbonates.

I assume you are referring to water without additional carbonates. The mash contains phosphates that act as buffers (reacting again with Ca in the water and malt). Each malt species and kiln treatment will change that "acidic contribution" or DI mash pH. With R/O I find I can hit 5.4 with all base malt for an APA, but including significant mineralization to help it along. On dark beers, such as a stout, I will need a small amount of baking soda or pickling to prevent the pH crashing past 5.2. Again - I am working in a more horse shoe world than precise, and making only small adjustments with verification in the mashing process. I always have a 0.1 pH adjustment handy for either direction should I need it. 5.4 is conveniently in the middle of the general 5.2 - 5.6 recommendations - so a miss by 0.2 in either direction, while not optimal, won't ruin the beer.

AJ's proton deficit modeling is significantly more precise, but also dependent on more precise measurement than available widely today (that is in available reference, not in personally doing the DI mash measurements) - so accounts for acid necessary to bring malt DI pH to a desired level. His spreadsheet can account for additional ion concentrations available as well. Not a criticism.

I understand, but may be wrong, that boiling will cause Ca to combine and precipitate (enhances break formations), freeing protons and acidifying the wort (a gross generalization). Additional remaining alkalinity will resist that transition and may come from too high a pH in the mash (at equilibrium above 5.5/5.6) or high pH sparging, artificial additions, such as baking soda or pickling lime intending to move pH upward. Danger comes when we manipulate too much in the mash process - and not account for slower reactions.

I'm supposing then, that because h-bar's beer is fine without it, and mchrispen calls it a 'tweak', is just not very relevant either.

Not sure I follow. Mg and Na, while having some impact on mash pH are negligible in the general calculation. Relative to determining additions, and computing "exact" amounts to achieve a specific pH, we are dealing with imperfect mash modeling. This leads me Mg and Na are less important to managing mash pH (though they have a minimal role) and more important to matching specific flavor contributions where required by style. Some of this could be implied by looking at historical water profile information or by a culinary approach by adding enough to get the desired flavor effect. I lean this direction because focusing first on Ca and Bicarb to fix a ballpark mash pH, and flavor ions as a secondary consideration (but also important) has worked well for me as a procedure.

If boiling reduces in pH and so does fermentation, would these pH reductions be enhanced with very little buffering activity (no carbonates)?

Yes, but the degree of "reduction" is dependent on all things upstream of the final product (water composition, grist, mashing schedule, mineral and acid and base additions) that may contribute alkalinity. We also know that yeast prepare their fermentation environment by controlling pH, but within limits. Outside of those limits, fermentation is not optimal.

So, then, all malt mash provides all buffering necessary?

Only when the alkalinity of the liquor (and the sum of the alkalinity of any mineral additions) is equal to the acid contributions of the mash to stabilize at or near 5.4 mash pH. So it depends.

EDIT - AJ answered much more specifically. I love concurrent posts!

 

[ldave]

I thank you folks for your knowledgeable input on this subject. My basic question is well answered. I've only just secured the Water book 3 days ago, so it's clear I have much more to absorb out of it. But it does look like going the RO route and building water will be very instructive both in the pH control department and the flavor contribution of various minerals. I see a whole new category of notes coming to my brewing notes.

BTW, I bought the Yeast book at the same time. I'm absorbing that at the same time. Quite a bit there, as well.

 

[ajdelange]

The mash converts carbonates to end products that take the carbonates out of the alkaline game, reducing pH. As the reaction is limited by the amount of Ca (and this must be the core reason for Ca inclusion),...

The calcium doesn't have anything to do with it (other than third order effects relating to ionic strength. It is simply HCO3- + H+ --> H2CO3 --> H2O + CO2. Calcium is only important if you are heating to decarbonate in which case bicarbonate leaves at both ends:

Ca++ + 2HCO3- ---> CaCO3 + CO2 + H2O. Note that there is no pH shift here as the proton yielded up by one of the bicarbonates in converting to CO3-- is taken up by the other in converting to H2CO3.

, at endpoint, if pH>grist DI of 5.655 then you still have unwanted water carbonates and these are what is titrated against with an acid addition.

If the water originally contained carbo then there will be some left at pH 5.655 in the form of bicarbonate and acid will be required to convert that to H2CO3 and lower the pH.

In the case of no water carbonates present, to get from grist DI pH=5.655 to pH=5.4 the acid titration proceeds against alkalines (presumably carbonates, as well) present in the malt.

Aside from the bicarbonate in the water there are other basic anions in the malt and they will absorb protons as surely as bicarbonate ions will. These bases are probably not bicarbonate. The prevalent is doubtless phosphate though there are others (succinate(?) malate(?) dissociated amino acid side chains...)

The presence of these, then, provides the buffer capacity of the wort for subsequent boil and fermentation in the absence of water carbonates. Am I close?

These bases do provide some resistance to pH shift and thus buffering. When it comes to the boil, however, the calcium reaction is back in play with the formation of additional calcium phophates and complexes of calcium with proteins releasing more hydrogen ions.

 

[h-bar]

h-bar: Did you acidify at all with just gypsum and CaCl? And did you measure pH?

I added acid malt to the grist. Sorry, I should have mentioned that. And no, I'm too poor to have a pH meter. (someday!)

 

[ldave]

The calcium doesn't have anything to do with it (other than third order effects relating to ionic strength. It is simply HCO3- + H+ --> H2CO3 --> H2O + CO2. Calcium is only important if you are heating to decarbonate in which case bicarbonate leaves at both ends:

Ca++ + 2HCO3- ---> CaCO3 + CO2 + H2O. Note that there is no pH shift here as the proton yielded up by one of the bicarbonates in converting to CO3-- is taken up by the other in converting to H2CO3.

I think I get that. What I meant by 'the mash' was before you add acid. At that point, the H+ ion in this:

HCO3- + H+ --> H2CO3 --> H2O + CO2

is coming from a Ca reaction in the mash. And is therefore limited by Ca. Once the Ca completely goes to calcium phospate, no more H+ ion, no more carbonate consumption. Correct?

Once that pathway is exhaused, add acid and the reaction continues. Correct?

Bear with me, it's been 20+ years since chem.

 

[ajdelange]

At that point, the H+ ion in this:

HCO3- + H+ --> H2CO3 --> H2O + CO2

is coming from a Ca reaction in the mash. And is therefore limited by Ca. Once the Ca completely goes to calcium phospate, no more H+ ion, no more carbonate consumption. Correct?

OK, I see what you mean but the calcium reaction with phosphate is only one potential source of protons. Others are acids you add and any malt that has an intrinsic pH lower than the current pH of the mash

Once that pathway is exhaused, add acid and the reaction continues. Correct?

Yes but one usually adds the other acid, if any, to the water so that the water's alkalinity is nullified (if only partially) and any left over plus any in the grist is there to neutralize the alkalinity of the base malt.

 

[ldave]

Quote:
Originally Posted by ldave
Once that pathway is exhaused, add acid and the reaction continues. Correct?

Yes but one usually adds the other acid, if any, to the water so that the water's alkalinity is nullified (if only partially) and any left over plus any in the grist is there to neutralize the alkalinity of the base malt.

Ah, I never thought about doing it that way. While I do acifify the sparge water, I don't do any pH adjustment regarding the mash/water until it sets up at mash temp and stands about 10 mins or so. So, I allow the intrinsic pathway to execute then add acid to continue pH reduction. Use a pH meter and add to pH=5.4. I never thought about acidifying the mash water first.