Increase in pH after Boil - Explanation

[jmhbutler]

I just brewed a hefeweizen tonight and found a weird shift in pH I was hoping somebody could help rationalize.

I usually aim for a post boil pH of 5.2-5.3 and experience a small pH drop during my boil. I often add a small amount of calcium chloride or a few drops of lactic acid to aid this drop.

This particular brew I measured a pre-boil pH of 5.39. I added 1g of calc chloride and boiled for an hour. Upon testing my final pH (taken from the hydrometer) I noticed an increase in pH of 0.13 up to 5.52.

Can anybody explain what happened here? Could the trub in the sample be impacting pH? Could something on my submersible copper chiller be acting as a base?

Help!

 

[ajdelange]

The best explanation I can offer is measurement error caused by pH meter drift. Otherwise I cannot explain an increase in pH during boil. All the theory says it should decrease. There may be circumstances in which the theory doesn't apply but I don't know what they are.

 

[Colbizle]

I just brewed a hefeweizen tonight and found a weird shift in pH I was hoping somebody could help rationalize.

I usually aim for a post boil pH of 5.2-5.3 and experience a small pH drop during my boil. I often add a small amount of calcium chloride or a few drops of lactic acid to aid this drop.

This particular brew I measured a pre-boil pH of 5.39. I added 1g of calc chloride and boiled for an hour. Upon testing my final pH (taken from the hydrometer) I noticed an increase in pH of 0.13 up to 5.52.

Can anybody explain what happened here? Could the trub in the sample be impacting pH? Could something on my submersible copper chiller be acting as a base?

Help!

What kind of PH meter are you using? Did you take all your PH readings at the same temperature? I have a PH meter with automatic temp adjustment but I still find that if the temp at the time of the reading isn't the same as the other readings then the reading will be slightly off.

 

[SnakeRidge]

Temp will affect pH. I think even the temp correcting meters are only good up to 160* or so. You only concentrate the wort during the boil, you don't add any ions. Dilution/concentration has no effect on pH.

 

[Colbizle]

Temp will affect pH. I think even the temp correcting meters are only good up to 160* or so. You only concentrate the wort during the boil, you don't add any ions. Dilution/concentration has no effect on pH.

I've never taken a ph reading higher then 75F...

I can't imagine what 160F would do to my $150 meter. I'm not willing to find out. :cross:

 

[ajdelange]

Temp will affect pH.

Temperature does effect pH in many cases but it also effects what the meter reads if you don't compensate for it. That is the function of ATC. See https://www.homebrewtalk.com/showthread.php?t=302256

I think even the temp correcting meters are only good up to 160* or so.

As ATC is wholly a matter of math (multiplying the slope measured at Tref by Tmeas/Tref) it can be applied at any temperature you like. Electrodes may have temperature design limits and the temperature measuring circuit in the meter may have limits.

You only concentrate the wort during the boil, you don't add any ions. Dilution/concentration has no effect on pH.

As you boil away water the concentration of hydrogen ions goes up and so the pH of the liquid goes down. Concentrated sulfuric acid has much lower pH than dilute sulfuric acid.

 

[SnakeRidge]

As I was typing that, I knew you would have corrections AJ. I work with biological buffers like Tris and know that diluting my pH'ed stock solutions doesn't change pH. Makes sense that it's not a blanket rule. Thanks for the info.