Quality control for yogurt production - Titratable acidity or pH?

Hi guys

Hoping you can assist me. I recently graduated and this is my first job as a food scientist and I am not 100 % sure of the following :headhurts: : 

We are busy with the development of an ambient drinking yogurt shake. Thus far I have measured only the pH of the product, and not determined total acidity. 

I use pH to determine when I will stop fermentation and whether the final product is in spec. Is this sufficient in terms of quality control of the product, or must I measure titratable acidity as well? 

If so, when in the production process is this done, and how often? I know the titratable acidity gives me an approximation of the total acids in the product, but how do I know if it is too high or too low, as total acids cant be directly linked to pH? 

If you have any clarity, or suggestions as to what I should test when and how often I would really appreciate it! 

Also, is flow rate/viscosity a quality control parameter on yogurt drinks? I have read articles which say it isn't usually because the measurements are never consistent. Would appreciate advice! 

Have a nice day,

Anna

I do not know the specific answer but I will tell you this golden rule on product development---

TEST EVERYTHING

especially given the product you are trying to produce.........the more information you have, the safer the product will be

Also, some acids are buffered by other ingredients so may or may not affect pH