Phosphoric Acid and Calcium precipitation (as Calcium Apatite)

[Silver_Is_Money]

I perused the Palmer/Kaminski "Water" book's charts found in Appendix C for acidification with Phosphoric Acid with respect to how many mg/L (ppm) of Ca++ ions you can keep in solution before your waters Calcium will precipitate out as Calcium Apatite. This perusal was undertaken in consideration of the oft mentioned concern that the use of Phosphoric Acid can cause one to lose calcium. And indeed the concern appears very real for certain circumstances (presuming that I'm reading the charts correctly). The charts scale for the solubility of Ca++ is logarithmic, so be careful when reading it.

For the specific case of source water with an initial pH of 8.0 and a targeted pH of 5.5 via acidification with Phophoric Acid, and presuming that I'm reading the charts correctly, here is how much Ca++ you can maintain in solution for various initial mg/L Alkalinities (as CaCO3):

Example for targeting 5.5 pH:
1) For water with 50 mg/L initial Alkalinity, Calcium Apatite precipitates out at and above ~420 mg/L, leaving 420 mg/L as the upper limit for Ca++ in solution
2) For water with 100 mg/L initial Alkalinity, Calcium Apatite precipitates out at and above ~180 mg/L, leaving 180 mg/L as the upper limit for Ca++ in solution
3) For water with 150 mg/L initial Alkalinity, Calcium Apatite precipitates out at and above ~110 mg/L, leaving 110 mg/L as the upper limit for Ca++ in solution
4) For water with 200 mg/L initial Alkalinity, Calcium Apatite precipitates out at and above ~78 mg/L, leaving 78 mg/L as the upper limit for Ca++ in solution

Water with an initial pH lower than 8.0 will hold a bit more calcium in solution, and water with an initial pH above 8.0 will hold somewhat less in solution. But not significantly.

If you target a lower pH than 5.5 the calcium you can keep in solution when acidifying with Phosphoric Acid increases rapidly and dramatically. The flip side is that if you target a pH above 5.5 things get way worse in a hurry. But by 5.2 pH as the target the values improve dramatically, and look like this (again for the specific case of source water at pH 8.0 initial):

Example for targeting 5.2 pH:
1) For water with 50 mg/L Alkalinity, Calcium Apatite precipitates out at and above ~1,260 mg/L, leaving 1,260 mg/L as the upper limit for Ca++ in solution
2) For water with 100 mg/L Alkalinity, Calcium Apatite precipitates out at and above ~1,100 mg/L, leaving 1,100 mg/L as the upper limit for Ca++ in solution
3) For water with 150 mg/L Alkalinity, Calcium Apatite precipitates out at and above ~780 mg/L, leaving 780 mg/L as the upper limit for Ca++ in solution
4) For water with 200 mg/L Alkalinity, Calcium Apatite precipitates out at and above ~500 mg/L, leaving 500 mg/L as the upper limit for Ca++ in solution

Moral of the story: If you are going to acidify your water with Phosphoric Acid, and your water has high alkalinity, and you are intending to have loads of calcium in solution, target a water pH adjustment of ~5.2 and you should be fine. If however you are merely trying to reduce Alkalinity to an Alkalinity target that does not drive the source waters pH down to below 5.5 (such as for the preparation of desired higher alkalinity mash water to counter the acidic grist of a Stout, whereby leaving alkalinity behind is essential) you may indeed lose appreciable amounts of calcium unintentionally if you choose to acidify with Phosphoric Acid, with much of this dependent upon your waters initial Alkalinity level.

Everything rests upon my having interpreted the charts correctly. Please verify if I have done so. Don't shoot the messenger. All of the above can be corrected if needed upon verification of accuracy.

 

[mabrungard]

Yes, the whole calcium precipitation issue is overblown. The water would have to have a very high calcium content before an appreciable amount of calcium would be precipitated. In addition, loosing some of that already high calcium content is INCONSEQUENTIAL since elevated calcium provides no benefits.

 

[Silver_Is_Money]

I don't necessarily see it that way. As an example: To say the least, there is a lot of negativity in the UK toward using Phosphoric Acid, and there are ugly pictures on some of their forums of calcium dropping out of solution when using it for water acidification (with comments that this only happens with Phosphoric Acid). In general they desire to brew with noticeably higher levels of calcium, and they generally have relatively high alkalinity water, even when it comes from a local water authority, plus they seem to be highly averse to purchasing and installing RO units (and they often laugh at us for using them, even believing that we must use them because water is filthy and contaminated here vs. water in the UK). And on top of that, they seem to favor targeting remaining alkalinity (to style) rather than pH when they acidify their water, and the alkalinity they target is often higher than the accepted norms here in the USA. A better answer might be: 'It depends'.

 

[Silver_Is_Money]

Since the UK favors AMS (CRS) over Phosphoric Acid for alkalinity reduction, does anyone know why this product (or a knockoff) is not available anywhere within the USA?

 

[Srmatt]

Yes, the whole calcium precipitation issue is overblown. The water would have to have a very high calcium content before an appreciable amount of calcium would be precipitated. In addition, loosing some of that already high calcium content is INCONSEQUENTIAL since elevated calcium provides no benefits.

So, for us uninformed noobs, what would a very high amount be ppm?

 

[Silver_Is_Money]

So, for us uninformed noobs, what would a very high amount be ppm?

If you use Phosphoric Acid it depends upon the alkalinity of your water. See post #1 in this thread.

That said, for many homebrewers in the UK (who do not often choose to use Phosphoric Acid) I would guess that about 150-180 mg/L (~ppm) Ca++ ion is considered to be ballpark ideal, so 'perhaps' at about 250 mg/L (~ppm) they would see Ca++ as becoming excessive. But cire is the one to ask here as to calcium limits in the UK, so I hope he drops in to comment and offer correction to my presumptions.

 

[cire]

Phosphoric acid was not used by British brewers for reducing alkalinity, its use in the brewery being limited to yeast washing and other cleansing purposes.
Standard calcium levels for British style ales are 100 to 200 ppm, and to avoid calcium sedimentation, salts are often added, at least in part, to the grains. I never add salts to my liquor, my water contains 80 ppm calcium and the rest is either added to the grains or to the boil.

Sulphuric, hydrochloric and AMS, a mixture of the the other two, are the most commonly used acids in breweries to reduce alkalinity.

The UK became aware of phosphoric acid for acidifying brewing liquor when US homebrewers began posting on British homebrew forums, but within a short time there were reports from all hard water regions of the UK of large deposits in the HLT by those trying that acid.

The examples charted in the first post are flawed. They imply that as phosphoric acid is added, calcium may be deposited, but magically somehow goes back into solution as more acid is added. Apatite is insoluble, and is what makes fishbone.

There are homebrewers in UK who use phosphoric acid, but they tend to be in soft water areas or use it to brew lager when lactic acid might leave a twang in the beer.

Water softening in UK is limited to washing machines and not for supplies for health reasons. Only one company supplies RO water in UK, starting in 2019 and most people are at least 50 miles from the nearest outlet. Some homebrewers have RO systems installed at home. Most traditional brewers use well or supply water, Britain is a small country and it rains all year. The major brewers use RO water to replicate the most advertised national lagers.

 

[Silver_Is_Money]

If you add Ca(OH)2 [Calcium Hydroxide, Slaked Lime, or Pickling Lime] to your mash water as a source of Ca++ (calcium ions) you had better not use Phosphoric Acid.

10Ca(OH)2 + 6H3PO4 → Ca10(PO4)6(OH)2 + 18H2O

Per Wikipedia, it goes straight to the form of Calcium Apatite known as Hydroxyapatite [Ca10(PO4)6(OH)2]. Up to 50% by volume and 70% by weight of human bone is a modified form of hydroxyapatite, known as bone mineral. Carbonated calcium-deficient hydroxyapatite is the main mineral of which dental enamel and dentin are composed. And of course it is virtually insoluble, so it drops or settles out. And as a consequence all of the calcium you thought would be of benefit to your Wort (and eventually beer) is instead lost.

Edit: Yet another reason for not using Ca(OH)2

 

[cire]

There would seem to a huge amount of doubt about the way British beers are made.

The link below might dispel some of the myths that exist about British brewing, the piece on water treatment starts 19 minutes 30 seconds in, and yes, their water has 400 ppm alkalinity.

 

[Srmatt]

If you use Phosphoric Acid it depends upon the alkalinity of your water. See post #1 in this thread.

That said, for many homebrewers in the UK (who do not often choose to use Phosphoric Acid) I would guess that about 150-180 mg/L (~ppm) Ca++ ion is considered to be ballpark ideal, so 'perhaps' at about 250 mg/L (~ppm) they would see Ca++ as becoming excessive. But @cire is the one to ask here as to calcium limits in the UK, so I hope he drops in to comment and offer correction to my presumptions.

Thanks!