Beer Forum

I understand that malt phosphates number in the 1 percent range in the typical wort. I haven't really studied malt phosphates in detail, but I know that AJ has. Those phosphates are the basis for the Ca and Mg reactions and subsequent proton production and pH drop.

AJ, are you saying the phosphatic ions from the dissolution of phosphoric acid are similar to those of the malt phosphates? If they are, then would the addition of minor amounts of phosphoric acid actually promote the additional Ca compound precipitation that Colin is mentioning? I'm really trying to get a better grasp on the reason that adding phosphoric acid would be the genesis of additional Ca precipitation.

The other thing I'm trying to grasp is if precipitating some extra Ca from solution by phosphoric acid addition is really that detrimental to the ferment performance?

CaPO4 is basically insoluable at wort pH. It is called Calcium Phosphate and it is what your bones are made from. MgPO4 also precipitates but it is about 50% soluable at a pH of 5.2 so it does not reduce the pH as much. If you are adding phosphoric acid to water that is low in Ca then it is important to add a little Ca to the boil for yeast health. Lager brewers use the rule of thumb that you add 2/3 of you salt additions to the mash and 1/3 to the boil. Since I make waters that are very high in Ca I don't add Ca to the boil.

The lowest Ca beer I make has 10 ml of 88% Phosphoric Acid, 600g of CaSO4 and 50g of CaCl in 300 gallons of RO water. I assume that it is enough to allow Ca into the fermentation. This is also the only beer I make that has more acid than it takes to reduce the alkalinity to 0! Usually I reduce the akalinity to between 20 to 60 ppm as CaCO3. The lower numbers for lighter color beers.

Acourding to one of my favorite brewing texts 1% of the weight of malted barley is phosphate!

http://books.google.com/books?id=bHuCdG ... te&f=false

Also Malted Barley as phytase to convert phytate into phosphates efficiently. This tells me the CaPO4 reaction is limitid by Ca and likely vary little Ca survives into the fermentation. I will start adding a little Ca to the boil and see if it changes my yeast performance.

mabrungard wrote:I understand that malt phosphates number in the 1 percent range in the typical wort. I haven't really studied malt phosphates in detail, but I know that AJ has. Those phosphates are the basis for the Ca and Mg reactions and subsequent proton production and pH drop.

The number I always see is that phosphate, as the pentoxide, comprises 2% of the weight of malt. As phosphate that would be about 1.4% as phosphate. So at 1 quart (2 lbs) of water per pound of grain and assuming that all the phosphate got released into solution you would indeed have approximately 1% w/w.

mabrungard wrote:AJ, are you saying the phosphatic ions from the dissolution of phosphoric acid are similar to those of the malt phosphates?

AFAIK yes. They are held in the grain as a salt of inositol hexaphosphoric acid which, subject to the action of phytase releases inorganic phosphate ions and myoinositol. Furthermore, apparantly some of the phosphate is able to chelate calcium and magnesium even when still attached to inositol hexaphosphoric acid.

mabrungard wrote:If they are, then would the addition of minor amounts of phosphoric acid actually promote the additional Ca compound precipitation that Colin is mentioning?

It would in Colins case because he is adding phosphate to water which contains no other phosphate i.e. he's doing it before adding any malt. Looking at the numbers I ginned up last night, however, it doesn't appear that much calcium is being stripped out by the phosphate and that's assuming a pretty high pH (8.3) to start. Given that his pH were say 7.7 to start it would take less H+ to get to 7.2 and require less precipitation of calcium with phosphate. If one holds off on using phosphoric acid until the mash, for example to move a mash pH of 6 or 6.2 to 5.4 or so then I would think even less would precipitate. In any event as the example calculation seems to indicate the amount of phosphate added to move pH is small compared to the amount of phosphate in the malt.

mabrungard wrote:I'm really trying to get a better grasp on the reason that adding phosphoric acid would be the genesis of additional Ca precipitation.

Me too. It's pretty complicated to figure out what's really going on as you have to simultaneosly satisfy Henry, Henderson Hasselbalch for 5 pK's (2 for carbonate and 3 for phosphate), 2 solubility criteria and neutrality in the simplest model which is that carbonic and phosphoric are the only acids present. But the general principal is that appatite is extremely insoluble to the extent that where phosphate is present at the gram/L level even minute amounts of calcium saturate the solution at pH's above 5.4 or so and precipitation occurs. Phosphate softens water - even at relatively low pH.

mabrungard wrote:The other thing I'm trying to grasp is if precipitating some extra Ca from solution by phosphoric acid addition is really that detrimental to the ferment performance?

That will depend on how much alkalinity you need to combat and how much calcium is available. If you have water with alkalinity 300 ppm as CaCO3 it's going to take about 6 meq/L (120 mg/L) calcium to drop it to pH 5.2 with phosphoric (acid added plus acid from malt). OTOH if your alkalinity is 50 it's only going to take out 1 meq/L (20 mg/L). If you do what Colin is doing and my hypothesized characteristics for his water apply then phosphoric acid doesn't remove that much calcium because not that many protons (0.247 meq/L) are needed to drop the pH of 100 ppm alkalinity water from 8.3 to 7.2. But then the alkalinity isn't reduced much either - 12 ppm.

Eventually most of the rest of the alkalinity (94% of it) has to come out to get to mash pH 5.2 so assuming he starts with 100 ppm (2 meq) he'll need 94/50 = 1.84 mEq protons and 1.84 meq calcium (all /L) precipitated to get the water to mash pH by the phosphate mechanism. That's 37 mg/L which isn't so much. But then there's the acid needed to get the mash from distilled water pH (say 5.75) to desired pH (say 5.4). That's a shift of 0.35 pH which divided by Kolbach's 0.00186 pH/ppm_as_CaCO3 gives another 208 ppm calcium hardness which needs to be sacrificed. This is 83 mg/L which is quite a bit and which, with many waters, would have to be added.

Colin Kaminski wrote:
The lowest Ca beer I make has 10 ml of 88% Phosphoric Acid, 600g of CaSO4 and 50g of CaCl in 300 gallons of RO water. I assume that it is enough to allow Ca into the fermentation. This is also the only beer I make that has more acid than it takes to reduce the alkalinity to 0! Usually I reduce the akalinity to between 20 to 60 ppm as CaCO3. The lower numbers for lighter color beers.

So you have added 135 mg/L calcium and about 0.127 mEq/L protons from phosphoric acid (pH should go to about 6.83). Thus 0.127 mEq/L calcium should precipitate. This is 5.4 mg/L. You should have plenty left in the water!

Then the drop from an assumed DI water mash pH of 5.75 to a target pH of 5.4 would require 20*(0.3/0.00168)/50 = 71 mg/L additional (precipitated with malt phosphate) for a total of 75 leaving 60 mg/L going forward into the kettle.

Though I probably don't have to say it, this is all very "back of the envelope".

Thank you AJ, I don't have any problems hitting 5.2 with this recipie even though the color is very light. I do notice I drop a little more pH in the boil so I assume the reaction continues. How would heat effect CaPO4 solubility and reaction rate?

That's to be expected and I think it testifies to the fact that you are carrying over calcium into the boil as the reduction is attributed to calcium precipitation with phosphate and and with proteins and peptides.

As to the reaction rates: I'm sure they go up with increased temperature.
As to the solubililites of the complexes: don't really know but enough calcium salts become less soluble with increased temeperature I'm guessing that these do too. The fact that boiling decreases pH when calcium is present suggests that this is the case.

ajdelange wrote: If one holds off on using phosphoric acid until the mash, for example to move a mash pH of 6 or 6.2 to 5.4 or so then I would think even less would precipitate. In any event as the example calculation seems to indicate the amount of phosphate added to move pH is small compared to the amount of phosphate in the malt.

AJ, excellent information. So to reiterate:

Adding phosphoric acid to the mash would be preferable to adding it directly to the water before mashing? In the case of sparge water acidification, it appears that phosphoric acid may not be an ideal choice if the brewer expects to carry over the same calcium concentration into the wort. That effect would still be minor if I understand your analysis result.

The quantity of phosphate in the mash is larger than the quantity of calcium supplied by the water, but I take it that the precipitation reaction cannot go to completion in the mash because the phosphate in the malt is not in an acidic form. Would that be the case?

The calcium phosphate precipitation is not a huge factor in the overall carryover of calcium into the wort. Looking at Tables 7.5 and 7.6 of Malting and Brewing Science confirms that although there may be a reduction in the calcium concentration, it appears to be minor. Is that in line with your findings?