pH rising during boil

[Jack of all biers]

The title is to grab your attention, but it is also accurate. I didn't want to post this in Adjuncts or Equipment streams as I am not sure it is either.

Since I purchased a pH meter last year, I have been religiously recording the pH of the various stages of my brews and have noticed that sometimes the pH rises post boil compared to pre-boil and mash pH readings. The rise of pH is not drastic, but I am curious to see if there is a possible explanation for this or if others have had the same experience.

So since purchasing the pH meter (Horiba LAQUA twin pH22, resolution 0.01, accuracy +/- 0.01, three point calibration (I only calibrate 7 & 4), temp compensated) I have measured 4 brews. All my pH measurements are taken within the temp range of 20-25C (measured).

1st brew (Milk Stout) seems to have lowered pH during boil from pre-boil 5.30 to post boil 5.14 (It did have a decent wack of Invert sugar 500gm and lactose 500 gm added to the boil, so this alone should lower pH).

2nd brew (IPA) went from pre-boil 5.58 to post boil 5.85 (I re-calibrated the meter, thinking it was user error, but the next test showed 5.92). At this point, I thought I must have made an error and not mixed the wort enough, ending up with stratification layers that affected my results. I put it out of my mind.

3rd brew (EPA), I forgot to take pre-boil pH, but mash pH was 5.17, first runnings 5.10, end runnings 5.71 and post boil 5.19. This confirmed (or so I thought) that the previous tests were an error on my part.

4th brew (Vienna SMaSH) went from pre-boil 5.46 to post boil 5.59. The pre-boil was taken after a thorough stirring of the wort and circulating 2L of wort through the tap to ensure the potential issue of the 2nd brew above was not a consideration.

All of the above brews had only hops (Hallertau Pacific and/or East Kent Goldings) and the recommended amount of Whirlfloc and Yeast nutrient (no brand, but bought from LHBS) added to boil (except the Milk Stout as indicated above). So my thoughts are, if Whirlfloc or the yeast nutrient I add towards the end of the boil (last 10-15 mins) changed the pH then others would have experienced this and asked the question, but I could not find anything about that.

So is it indeed user error? Equipment error? Possible mashing issues affecting the outcome of the boil? Not enough Calcium in the wort pre-boil to assist pH reduction in the boil (most of my above worts were in the range 50-85 pmm Calcium and all Calcium salt additions were made to the mash tun alone)?

Re equipment error, maybe two indicators would suggest this is not the case. Mash pH results are consistent over the period of all my mashes and are consistent to those that are predicted by Brewers Friend. Also, pH tests of my water (mains and rain water) also seem to be accurate and consistent over a period of readings.

I'm not overly concerned, but given boiling should be reducing wort pH, it is a conundrum. Below is an excerpt from 'The function of wort boiling'

It is important to achieve the required
decrease in pH (generally around pH 5.0) as it
effects wort and beer character, in particular
the fall:
• Improves protein coagulation
• Improves beer flavour in particular VDK
(diacetyl) reduction
•Encourages yeast growth
• Inhibits the growth of many other
contaminating organisms.
• Lower pH results in poorer hop utilisation.
• Lower pH results in less colour formation

 

[damoninja]

That's a pretty small drop.

Evapouration?

Is it there correlation with your pre/post boil volumes?

 

[Jack of all biers]

I'm away from my laptop and therefore my notes, but I generally lose 3-4 L per boil. Last brew was 57L @ 80 C (~55 L @ 20C) pre-boil and 51L @ 80C (~49 L @ 20 C) post boil

 

[Jack of all biers]

3-4 L evaporation. Other losses are hops, grub and minimal dead space.

 

[HBHB]

Is the base water high in carbonates?

 

[TSMill]

I would suggest you are driving co2 out of solution in the boil, which will increase pH.

 

[Jack of all biers]

Is the base water high in carbonates?

Well for the first three above the water was from the mains and the water company provided the carbonate level for that year as 0. See attached for all levels provided. View attachment Adelaide water data - Central Metro System - 2015-2016.pdf

The last brew was rain water from my tank. Nice and clear so I take it that it is 0. Measured pH of the rain water for this brew was 6.59 @ 23C.

I would suggest you are driving co2 out of solution in the boil, which will increase pH.

Sorry, but can you expand on this? I wasn't aware that CO2 is produced in the mash.

 

[Jack of all biers]

That's a pretty small drop.

Evapouration?

Is it there correlation with your pre/post boil volumes?

Yep my memory was spot on. Checked my notes and each brew consistently lost about 3-4 L in evaporation, with the rest to hops, dead space and trub.

 

[Lyrebird_Cycles]

Take 2 or 3 samples from each of the various stages and put them in the fridge until the next day. Take them out of the fridge into a water bath to equilibrate to 20 degrees. Calibrate the pH meter and measure the pH of the samples in random order*. Group the results back into the stages represented and report.



* Use a random number generator or, at a pinch, a phone book. The phone book is an ancient trick to make a decent random number generator for no money: flip to a page and just assign the last three digits of the numbers in a column to each sample in sequence, pasting the assigned number over the sample ID. Test in numerical order of assigned number, the test order will be essentially random.