I was hoping one of you could help me. I am in the final stages of developing a fermented maize drink - and I am now struggling with a few practical issues regarding the pH measurements etc.
We incubate our maize slurry at 45 deg C for around 6-7 hours, upon which we achieve a pH of about 4.3. The starter culture we use is a mixture of S.thermophilus and L.bulgaricus. Our final product's pH should be 3.7-3.8 - which we will achieve with the addition of Citric acid.
When the slurry has reached a pH of 4.3 via fermentation at 45 deg C, we stop fermentation and add citric acid to further decrease the pH to our desired pH. We do this before the other ingredients are added, mainly because of our production process: We thermally package the product at 75 deg C, thus the other ingredients (sugar, flavours etc) are added at 65 deg C. Acidifying the product at this point will be even more inaccurate because of the high temperature.
The problem I am experiencing is that upon adding citric at 45 deg C, the pH drops significantly (from 4.3 to 3.0). Once the other ingredients are added, and the product has cooled overnight, the pH increases again to pH 4.0. This varies every time.
I have done a trial to see what effect each additive has on the pH, and compensated for that increase accordingly - however I am still not sitting with a final pH which is in spec.
I make use of a Hanna Yogurt pH meter which can compensate for temperature up to 50 deg C, with an Open Junction Electrode.
Is there a general rule of thumb, or any tables, which will allow me to calculate what pH the maize slurry at 45 deg C should be, in order to result in a pH within spec in the final product at room temperature?
I can't check the final pH before packaging, as due to us thermal packaging the product, it is too hot!
Any advice will be greatly appreciated!
Edited by Annamart21, 26 February 2019 - 08:06 AM.