Mash and boil pH

I'm on electrode #4 or 5 now, with my problematic Milwaukee pH meter.

This one seems to be working quite well, with little drift so I'm happy finally!

Yesterday, since I had a properly calibrated meter and no issues with brewing, I took several pH readings.

5.45 10 minutes into mash
5.38 20 minutes into mash
5.30 at beginning of sparge
5.30 into kettle
5.10 after boiling/cooling

I have heard some of the experts talking about the changes in pH during the process, but it was cool to see the drop as the mash became wort.

I assume the lowered pH after the boil is because the wort has the acids from the hops oils isomerized- is that a correct assumption? Or is there something else in the magic of the boil that is responsible for this happening?

Wort pH will fall from 5.6–5.8 at the start of boiling to around 5.2–5.4 at the end. This is primarily due to the precipitation of calcium phosphate. Calcium ions in brewing water reacts with phosphates from the malt to form calcium phospate and hydrogen ions, which lower wort pH.

This demonstrates the importance of excess calcium ions in the wort after mashing. For this reason, it is sometimes a good idea to add gypsum to the kettle. If your mash pH is fine, but the pH does not drop to at least 5.4 by the end of the boil, add 1/4–1/2 teaspoon of gypsum per five gallons.

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http://byo.com/stories/item/1650-wort-boiling-homebrew-science

Hops do, of course, contain acid but it is weak acid (the fact that boil pH effects utilization attests to this) so I expect hops influence on kettle pH is small compared to continued precipitation of calcium with malt phosphate (apatite) and with proteins.

In regards to adding Gypsum to the kettle, would adding Calcium Chloride ostensibly provide the same benefits?

Since taking more of an interest in my pH, I have realized better efficiency and notice little things (like hot break and clarity) improving.

@Yooper - which pH meter are you using? Is it a different/aftermarket probe that you've switched to?

pjdunn11 said:

In regards to adding Gypsum to the kettle, would adding Calcium Chloride ostensibly provide the same benefits?

Since taking more of an interest in my pH, I have realized better efficiency and notice little things (like hot break and clarity) improving.

@Yooper - which pH meter are you using? Is it a different/aftermarket probe that you've switched to?

Click to expand...

I'm using the Milwaukee 56. I just kept getting new electrodes (by the company) until I got one that actually seemed to work right! I've made a thread about it in the past, but it never worked correctly out of the box and was sent in twice, plus they've sent me a total of 4 electrodes. But now it seems to be just dandy with the latest one!

Am I missing something? It seems to me the pH would go down due to the wort being concentrated by the boil-off. More hydronium (H+) per volume = stronger acid.

Yooper I’m glad you finally got your drift-o-matic meter whipped into submission.

Wynne-R said:

Am I missing something? It seems to me the pH would go down due to the wort being concentrated by the boil-off. More hydronium (H+) per volume = stronger acid.

Yooper I’m glad you finally got your drift-o-matic meter whipped into submission.

Click to expand...

The pH did go down- it was 5.10 after boiling/cooling.

ShootsNRoots said:

http://byo.com/stories/item/1650-wort-boiling-homebrew-science

Click to expand...

Interesting.

Just checked the data on my last ~10 beers and found that my post-boil pH (room temp sample) is <5.4 for my hoppier beers where I'm adding a bunch of gypsum to the mash/sparge water and >5.4 for maltier beers where I'm not adding much gypsum (all with room temp mash samples in the 5.4-5.5 range).

Base water Ca is ~54ppm and I adjust mash/sparge water to ~75-100ppm to maltier beers and ~200ppm for hoppy beers.

Wonder if my maltier beer's wort is a bit low on calcium?

Yes Yooper, I get that 5.1 is less than 5.3. Apparently my point was not clear.

I don’t dispute the calcium phosphate thing, but it seems to me the boil-off concentration would account for about half the pH difference. Am I wrong or did AJ (gasp) miss something?

Seems to me the post boil pH should be considerably lower if you boil off a gallon or more from a 6.5 - 7 gallon pre boil volume.

If you had, for example, 0.001 N strong acid (like sulfuric) solution in water the pH would be about 3. If you boiled away half the water then you would have 0.002 N sulfuric acid and the pH would be about 2.7.

But if you have a buffer for a particular pH and molar strength x and then boil away half the water you have the same buffer but with molar strength 2x and the pH won't change that much.

Wort is more like the second case than the first. The protons released by apatite formation stress the buffer or, from another POV change the system to buffer at a different pH and removing water just increases the buffering strength of that new buffer.

Yeah. Apatite formation.

Over my head, but cool to read about

In the old days we said

3Ca++ +2H2PO4- --> Ca3(PO4)2 +4H+

Being wiser now we know that the salt most likely to precipitate is hydroxyl apatite (the stuff of which your teeth and bones are largely composed):

10Ca++ + 2H2O + 6H2(PO4)- ---> Ca10(PO4)6(OH)2 + 14 H+

I never checked the pH post-boil. Might start doing that.