Ph shift in Gose Sour

[Morrey]

I have done quite a few Gose sours and measured ph with an el cheepo $15 meter. I broke down (actually IT broke down, lol) and bought a Hach Pocket Pro+ Ph meter and simply love it!!!!

I just put a Gose in the fermenter yesterday having used my "new" Hach meter. OYL-605 lacto starter was pitched into cooled wort for kettle souring. Prior to the pitch, I adjusted the level from 5.35 to 4.5. I had hit my goal of 3.24 after 36 hours and boiled 60 minutes. My evap rate was a .85G loss during this boil.

Once cooled and before pitching yeast, I drew a sample to test OG, and I said what the heck, lets test this final ph. It had gone from 3.24 to 3.19, so am I attributing this drop to the wort concentration after losing .85G of a 5.5G batch? This is all I can think of. I am not critically concerned, but this is something I'll consider next time for precision control.

Thoughts, is this ph drop solely due to evaporation and concentration?

 

[ajdelange]

A good part of it probably. You decreased volume by 15%. If you increase the concentration of a lactic acid solution in DI water with pH 3.24 by 15% you would expect the pH to drop to 3.21. You are not, of course, in DI water but rather in a complex buffering system but note that you are less that 1 pH from the pK of lactic acid (3.86) where its buffering power is maximum.