phosphoric acid and calcium prcipatation

[mudshark]

Is there any way to calculate how much calcium is precipitated when phosphoric acid is added to the mash?

 

[ajdelange]

It takes pretty hard water for this to happen. There are some charts in the back of the Palmer book but they, as are all calculations involving precipitation a bit iffy.

 

[dstar26t]

Palmers book = Brewing Elements Water. I was surprised to learn that the more acid added, the less calcium precipitates.
Below is the example for 100 ppm. The charts come in increments of 50 ppm. Hope you don't mind I posted it AJ, found it in a google image search...click to enlarge:



I stopped using Phosphoric for this reason. I was having to use more than was needed (for last runnings pH control) in the sparge water, just to keep the calcium I wanted. I believe there was a negative flavor impact so I'm back to Lactic to prove it. With Lactic, I can get my alkalinity to just below 25 ppm (from 30-50) without worrying about calcium precipitating. With Phosphoric, the safe zone to keep the calcium was under 10 ppm which I think was overkill with respect to final runnings pH control.

 

[ajdelange]

Palmers book = Brewing Elements Water. I was surprised to learn that the more acid added, the less calcium precipitates.
Below is the example for 100 ppm.

This is because at the lower pH the (PO4)-3 ions convert to H(PO4)-2, and H2(PO4)- ions.

The charts come in increments of 50 ppm. Hope you don't mind I posted it AJ, found it in a google image search...click to enlarge:

Forgot this one is on my web site.

I stopped using Phosphoric for this reason. I was having to use more than was needed (for last runnings pH control) in the sparge water, just to keep the calcium I wanted....With Phosphoric, the safe zone to keep the calcium was under 10 ppm which I think was overkill with respect to final runnings pH control.

That doesn't seem right. The chart says that to acidify to pH 5.5 for most reasonable starting water pH's (down to 6.5) you should be able to have up to 600-700 ppm Ca++.

 

[mabrungard]

Calcium precipitation via phosphoric acid addition is a red herring. If your water has the high calcium content needed to enable precipitation, you don't need to worry about what the final calcium is in the first place. There is little need for calcium in brewing water and we have been led wrongly to worry about calcium in brewing.

I say there are 3 rules for calcium: 1) have at least 40 ppm Ca in the mash to help precipitate oxalate from the wort, 2) have at least 50 ppm Ca in the kettle if brewing ales, but you can have lower kettle Ca content if brewing lagers, 3) add calcium only as needed to provide the Cl or SO4 content you want in your brewing water.

 

[ajdelange]

Calcium precipitation via phosphoric acid addition is a red herring.

Yes, for the most part but it is something brewers should be aware of. For example, taking water with alkalinity 100 and acidifying it to pH 6 for sparging will result in a threshold calcium level of 25 mg/L. If the water contains more than that there will be precipitation. The obvious fix is to continue to acidify until pH reaches 5.75 where the calcium threshold is 50 mg/L or 5.5 where it is 160. Adding the additional acid should re-dissolve the precipitate but it may take some time for the system to come to equilibrium.

 

[dstar26t]

That doesn't seem right. The chart says that to acidify to pH 5.5 for most reasonable starting water pH's (down to 6.5) you should be able to have up to 600-700 ppm Ca++.

2 examples here. Both Double IPAs, based on the Heady Topper Clone recipe found on this forum, 12 gal post boil.

The first time I brewed it, I used Pearl base and no acid in the mash. Mash pH of 5.23 with just the Calcium in the water (135 ppm), added some Lime which resulted in 5.32 pH (168 ppm total Calcium now). Assuming water had 39.6 ppm Alkalinity, added 0.12 mL/gal 88% Lactic to the sparge water (6.47 pH) which netted a 5.34 pre-boil pH. This beer was delightful.

The second time I used Pauls Mild Ale Malt and missed mash pH high at 5.47 (typical for this malt I've found) so I added 1 mL Phosphoric which brought it down to 5.38 (5.40 target). Assuming the water had 39.6 ppm Alkalinity and pH of 8.00 and with the goal of keeping 135 ppm Calcium in the sparge water, I added 0.18 mL 85% Phosphoric per gallon to target 5.65 pH. After sparging, wort pH rose to 5.41. I've been targeting a pre-boil pH of less than 5.40 so I added 0.34 mL Phosphoric which resulted in a pre-boil of 5.38. This beer had a very harsh astringent bitterness. I added a bit more hops to the whirlpool compared to last time but I can't believe that harshness came just from the hops. Other hoppy beers have turned out harsh and coincidentally, I used phosphoric acid in them too.

I am still troubleshooting this harshness so it may not be the reckless pipetting of phosphoric but it's on my list. I will report my findings but I only brew once every 2 or 3 weeks and not always hoppy beers.

 

[ajdelange]

The second time I used Pauls Mild Ale Malt and missed mash pH high at 5.47 (typical for this malt I've found) so I added 1 mL Phosphoric which brought it down to 5.38 (5.40 target). Assuming the water had 39.6 ppm Alkalinity and pH of 8.00 and with the goal of keeping 135 ppm Calcium in the sparge water, I added 0.18 mL 85% Phosphoric per gallon to target 5.65 pH.

Eighty five percent phosphoric is about 15 N WRT pH 5.65 so 0.18 mL would supply 2.7 mEq. 3.785 L of water with 39.6 ppm alkalinity requires 3.785*39.6/50 = 3.0 mEq to get to pH 4.3 or so so this sounds about right.

After sparging, wort pH rose to 5.41.

Sounds reasonable.

I've been targeting a pre-boil pH of less than 5.40 so I added 0.34 mL Phosphoric which resulted in a pre-boil of 5.38.

Sounds reasonable too. And I don't think you would reach calcium/phosphate saturation at those levels. Even if you did the precipitation of some apatite shouldn't result in harshness.

This beer had a very harsh astringent bitterness. I added a bit more hops to the whirlpool compared to last time but I can't believe that harshness came just from the hops. Other hoppy beers have turned out harsh and coincidentally, I used phosphoric acid in them too.

I think you need to look beyond phosphoric acid as an explanation here. It is pretty flavor neutral and reduced calcium, if precipitation is indeed taking place, wouldn't explain harshness, at least not by any mechanism I am aware of.

 

[uncleleon]

Bump. Keep talking water wizards

 

[dstar26t]

AJ, thank you for looking at my observations. I will share any results. It could just be a whirlpool utilization or hop selection issue but it coincides with using water "knowledge" or lack thereof.

Nate

 

[Smellyglove]

I read somewhere above that one should use enough Ca in the mash to avoid oxelate. Are there any pitfalls by using just phosphoric in the mash (except for the oxalate) and adding salts for fine-tuning SO4/Cl just to the kettle?

 

[mabrungard]

Calcium concentration has to be somewhat high in order for phosphoric acid to have any effect on precipitating that calcium. Therefore, there is plenty of calcium left over for precipitating oxalate. Don't worry about using phosphoric acid.

 

[Smellyglove]

Calcium concentration has to be somewhat high in order for phosphoric acid to have any effect on precipitating that calcium. Therefore, there is plenty of calcium left over for precipitating oxalate. Don't worry about using phosphoric acid.

Thanks. I meant only phosphoric. Still good? Is there a reason to switch to lactic as I see some folks do? Like in Ca-areas of up to 100ppm?

 

[ajdelange]

!00 ppm Ca should not be a problem. There are some curves in the back of Palmer's book. Remember that at mash pH there is much less phosphate (PO4-3) than there is at nominal pH (7) so that any "calcium phosphate" that did precipitate can redissolve.

There is one reason to use lactic and that is that you may like the flavors it imparts. This would especially be the case where the lactic is added by means of sauermalz.

 

[Smellyglove]

!00 ppm Ca should not be a problem. There are some curves in the back of Palmer's book. Remember that at mash pH there is much less phosphate (PO4-3) than there is at nominal pH (7) so that any "calcium phosphate" that did precipitate can redissolve.

There is one reason to use lactic and that is that you may like the flavors it imparts. This would especially be the case where the lactic is added by means of sauermalz.

Right. Thanks! I'll start experimenting with that then. I've noticed the flavor lactic gives. Sort of like Sweet & Sour.