The pH of corn tortillas should be checked in two places: the corn grinder (molino) and in the baked tortilla. The masa that comes out of the Molino can be checked directly with a flat surfaced electrode. The flat surface electrode can be used for checking the pH of the masa (directly) and of the baked tortilla in water (see method below). The acids and alkaline ingredients used in corn tortilla manufacturing typically have fast reaction rates and reach equilibrium almost immediately. The pH of corn masa and baked corn tortilla are similar and strongly correlated. The pH of the corn tortilla is about 0.1 to 0.2 units higher than in the masa. The correlation of pH in the masa and tortilla will not be as good if the corn tortillas contain acids other than phosphoric and propionic, since the equilibrium may be slower. Checking the pH at the corn grinder is often adequate for pH control of corn tortillas. Checking the pH of the finished tortilla is needed for a HACCP program.
Select two standard buffers to bracket the anticipated pH of the tortillas to be tested. For example a pH 4 buffer and a pH 7 buffer would be adequate to measure the pH of a corn tortilla at a pH of 5.2. Follow the manufacturer’s instructions for the pH meter available. Flat surface electrodes are the most versatile in the tortilla factory. It is possible to measure the pH of masa samples with these electrodes. This is very useful when making adjustments to preservative metering systems right at the molino or mixer.
1. Grind tortilla into small pieces in a coffee grinder and take 10 grams of the ground tortilla sample and add it to a clean empty plastic beaker. Then add 90 grams or ml of distilled or deionized water.
2. Homogenize the sample for at least one minute with the hand held homogenizer or blender.
3. Immerse the rinsed and calibrated pH electrode into the sample and vigorously stir the electrode in the sample.
4. Note the pH after one minute.
5. Record this pH reading as the tortilla pH.