Alkalinity

[bb40bball]

I've read my water report and I get it.... except for alkalinity. It says the alkalinity is 210 mg/L. I keep trying to read about alkalinity but I just get confused. What does this mean?

 

[Singletrack]

High alkalinity resists your wort's best efforts to reduce the pH of the mash, resulting in higher than desired mash pH.

Mine is 235 mg/L as CaCO3, so I blend RO water, use CaCl and CaSO4, and add lactic acid. Water optimization is all part of the fun.

 

[bb40bball]

So how would you suggest I adjust my alkalinity? Sorry if this is obvious.

 

[Singletrack]

Well, I blend RO water, use CaCl and CaSO4, and add lactic acid.

If you brew extract and your water tastes good, you do not need to adjust for alkalinity. If you brew all grain, you should conduct a search on water adjustments. There is software that can be used to help, such as Brun Water. Good luck!

 

[ajdelange]

So how would you suggest I adjust my alkalinity? Sorry if this is obvious.

If you have been wallowing in it for years it is pretty obvious but if you are new to it it can be quite confusing because of the way it is quantified in North America. And some of the spreadsheets add to the confusion in the way they deal with it.

So what is it really? All the details are at
http://www.wetnewf.org/pdfs/measuring-alkalinity.html
and you might want to check that out but do so later. Less formally alkalinity is, with respect to a water report, the amount of acid that is required to reduce the pH of 1 liter of the water to 4.4 (or some other pH close to 4.4 depending on the particular lab). To measure it one takes a liter of water, sticks a pH meter probe in it and adds 1 N (that's the strength) acid in small measured increments noting the pH as he goes. When the pH reaches 4.4 he stops and writes down the number of mL of 1 N acid he has used. Each mL of 1 N acid contains 1 milliequivalent of acid so if the analyst used 3 mL he would note the alkalinity as 3 mEq/L.

In fact laboratories use 0.1 N acid and add it to 0.1 L of water as the smaller volumes are easier to work with but the result is the same: the alkalinity is the number of mL of 0.1 N added to 0.1 L of water. That's what they do in most of the world, anyway, but in North America the number is multiplied by 50 (for reasons I won't get into here). There is some rationale for doing this but it really causes more confusion than it is worth, IMO.

Thus, if the analyst used 3 mL of acid the alkalinity if 3 mEq/L would be expressed as 150 ppm as CaCO3 in the US and Canada.

Now lets suppose that a sample of water of alkalinity 3 mEq/L comes into a lab and the analyst starts to do the titration and, when he gets to 1.5 mL he gets called away for some reason and another guy comes along not realizing that 1.5 mL of acid has already been added. He decides to do his buddy a favor and do the determination for him so he starts to add acid to the sample. It clearly only takes 1.5 mL additional acid to get this sample to pH 4.4 and so he reports the alkalinity of it as 1.5 mEq/L or 75 ppm as CaCO3. And indeed that was the alkalinity of the sample as presented to him. This suggests how alkalinity is reduced: by adding acid.

HCO3- + H+ + Lac- ---> H2O + CO2 + Lac-

Here the acid is HLac (lactic acid) Note that 1N acid has 6.02E20 H+ ions in each mL and 6.02E20 lactate ions. This is 1 mEq of the former and 1 mmoL of the later. Note also that each H+ reacts with 1 bicarbonate so that an alkalinity of 3 mEq/L implies a bicarbonate content of approximately 3 millimoles (3*6.02E20 ions) of bicarbonate ions; approximately because not all the bicarbonate is converted to CO2 at pH 4.4 and there may be carbonate, CO3--, ions present as well both dependent on pH. But, approximately speaking, if you add 1.5 mEq of acid (1.5 mL of 1 N acid) to 1 L of water with alkalinity of 3 mEq/L you will reduce the alkalinity by 1.5 mEq/L and replace it with 1.5 mmol of the anion (lactate in this example). Note that 10% phosphoric acid is about 1 N while 88% lactic is about 12 N.

The other method is to remove the stuff that is absorbing the acid which is the bicarbonate ion, the only absorber of acid (hydrogen ions) in water of normal composition and pH out of the tap. If you add something like lime or lye to your water these also absorb H+ and result in alkalinity which is not tied to bicarbonate. Thus spreadsheets and calculators which treat bicarbonate content as a proxy for alkalinity do the user a disservice. Even so, in the water as it comes out of your tap, alkalinity is indicative of the amount of bicarbonate.

Bicarbonate can be 'removed' by diluting it down with bicarbonate free water. A liter of water containing 1 mmol of bicarbonate mixed with 1 L of distilled water will have, in the mix, a bicarbonate concentration of 0.5 mmol/L and its alkalinity will be reduced from 1 mEq/L to 1/2. Bicarbonate can be precipitated in the presence of calcium by heating

Ca++ + 2HCO3- --> CaCO3 + CO2 + H2O

or by the addition of lime

Ca++ + 2HCO3- + Ca(OH)2 ---> 2CaCO3 + H2O

Either method reduces alkalinity.

Note that base malts have alkalinity too as they absorb protons (H+) as pH is lowered to the desired range for best performance of mash enzymes. Thus, in very broad terms, alkalinity is a measure of the resistance of your malts and water to lowering of mash pH to the target range. Both alkalinity components must be overcome. With the water we can remove bicarbonate or neutralize it with acid. Malt alkalinity must be neutralized with acid.

 

[Singletrack]

If you have been wallowing in it for years it is pretty obvious but if you are new to it it can be quite confusing because of...

Yeah, like I said.

Thank you for coming to the rescue with the full explanation. As for "wallowing in it for years," I resemble that remark.

 

[Evan_L]

I've twisted my brain with this for a while. I usually pick things up quickly but this for some reason was tough. You might find that the more times you come back to it more and more makes sense and sticks. Recently watched this video and had my "aha" moment. Give it a watch, good stuff. Make use of the pause and rewind. The first time I watched it straight through and it was too fast. Slow down and make sure you get each slide before you move on.

[ame]https://www.youtube.com/watch?v=zJj__jEkFUE[/ame]

 

[ajdelange]

John's perspectives have changed somewhat as a consequence of writing the water book tho he still tries to hang a lot on RA. Not sure where he is on the sulfate:chloride ratio thing at this point. Anyway, suggest the book rather than this video for the current perspective if you want more info than in #5 and the link it contains.