Back again with alkalinity/bicarbonate issues

In my last several attempts to reduce/eliminate alkalinity from the mash liquor, I've ended up with a much lower mash pH than predicted. (Ex: starting water pH 7.6, CaCO3 105ppm, attempting to lower to 70ppm. Bru'n Water says .8 ml 86% phosphoric for 5.3 gal. Mash pH target 5.43, actual reading 5.19) Is there a formula to predict what adding .8 ml of 86% phosphoric acid to 5.3 gal of pH 7.6 water will net as a resultant pH? When I treat my sparge water, I have a target pH & will always add only about 1/2 the acid then drop by drop reach the target. I do treat the mash & sparge water separately. Perhaps I'm not phrasing my questions accurately, but it seems to me if I could target the predicted results of my acid addition, I could stop when I reach my target & the mash pH would be closer to my goal.

If you are confident of the acid's strength, adding a known quantity of that acid and observing the resulting water pH is somewhat similar to an alkalinity test. In this case, it appears likely that your water's alkalinity is not as high as you think it is.

The equations employed on the Sparge Acidification sheet were prepared by AJ and find that they are accurate.

Thanks, Martin! So if I were to use the sparge acidification page to adjust my mash water alkalinity, I could use the resultant pH from that as my target, correct? I believe my acid strength may not be true or my pipette may be off a little.

You can use the Sparge Acidification sheet to EVALUATE your tap water alkalinity. That is as far as I would take that.

With respect to your acid, 86% is an uncommon strength. Are you sure about that? However, your results suggest that the acid strength or dose is higher than assumed.

I must have typed that wrong it's 85%.

Any thoughts on an alkalinity meter?

I recommend diluting some of your stock Phosphoric Acid down to a more workable concentration, like 42.5%, 40%, 21.25%, 20% or whatever you fancy. At 85% a drop or two more or less can make a big difference.

Realize, your water's mineral composition can change (even dramatically) with the seasons.

logdrum said:

Any thoughts on an alkalinity meter?

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What about a cheap aquarium test kit for hardness? They are easy to use, cheap, and can give you a good estimate as to the alkalinity in your water.

Yooper said:

What about a cheap aquarium test kit for hardness? They are easy to use, cheap, and can give you a good estimate as to the alkalinity in your water.

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That's exactly what I was thinking.

IslandLizard said:

I recommend diluting some of your stock Phosphoric Acid down to a more workable concentration, like 42.5%, 40%, 21.25%, 20% or whatever you fancy. At 85% a drop or two more or less can make a big difference.

Realize, your water's mineral composition can change (even dramatically) with the seasons.

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Is this achieved simply by cutting w distilled water at the appropriate ratio? I'm assuming by weight...

logdrum said:

Is there a formula to predict what adding .8 ml of 86% phosphoric acid to 5.3 gal of pH 7.6 water will net as a resultant pH?

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Yes, the formulas are in the sticky at https://www.homebrewtalk.com/showthread.php?t=473408.

logdrum said:

... but it seems to me if I could target the predicted results of my acid addition, I could stop when I reach my target & the mash pH would be closer to my goal.

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You can easily do exactly that and be spot on whatever your acid strength or actual alkalinity. Add acid to mash water until you reach the desired mash pH. The alkalinity if the water is now 0. This is the alkalinity to mash pH but you don't really care what the alkalinity is at pH 4.3 or 4.4. Your goal is to zero it at mash pH. Do the same with the sparse water. When using a spreadsheet to calculate the total required acid (or base) addition tell it that the water's alkalinity is 0. If it tells you you need additional acid to neutralize the malt's alkalinity add it. If it tells you you need alkali then you have added acid to the water in excess by the amount of alkali. At this point you can either add the alkali which seems silly so remove a volume of the treated water corresponding to the excess amount of acid and replace with an equal volume of untreated water.

For example suppose your water's alkalinity is 100 and you are going to treat 20 L of it. 100 ppm as CaCO3 is 2 mEq/L and as you have 20L you'd need 40 mEq of acid to reach pH 4.4 but you don't want pH 4.4. you want, e.g., pH 5.4 (target mash pH) and would, thus, use about 36 mEq in 'titrating' the 20 L to 5.4. Note that 1 mL of 88% lactic acid supplies about 11.8 mEq (need to check that). Now suppose your spreadsheet says you need 3.6 mEq of alkali. The alkalinity of your untreated water is 36 mEq/20L and of your treated water 0. To add 3.6 mEq of alkalinity back in remove (3.6/36)*20 = 2 liters of the treated water and replace with untreated water.

Note that if no alkali addition is necessary you do not need to know either the water's alkalinity or the strength of the acid. Just titrate until you hit mash pH. If alkalinity is needed (and that should be rarely) then you do need to now the acid strength. You measure the alkalinity of the water when you titrate it.

logdrum said:

Any thoughts on an alkalinity meter?

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Hannah makes one and there are others out there. It is simply an automatic titrator.

Thanks AJ!

Ok, after I've zeroed out my alkalinity, I'll tell the software it's zero, do I also tell it the pH is 5.4 (or whatever I'm shooting for)?

Don't know about Bru'n water in particular but the general principle is that you tell your spreadsheet what pH you want and add acid (or base) until the proton deficit sums to 0 or tell it how much acid (or base) you are adding and fiddle with the estimated pH until the proton deficit goes to 0.

This may be confusing for you so just approach the problem as if you are brewing with RO water. As far as alkalinity is concerned you are.