Measuring pH, and when you are required to

Why this is a question at all

Most fruit jams are comfortably acidic and nobody needs to measure anything. The question arises because a determination exists above this craft that depends on acidity, and crossing into it changes what you are required to do. Whether you are over that line is not a matter of opinion or of how the jam tastes.

A standard jam or jelly is preserved by its sugar concentration. A product that departs from that, by cutting sugar, adding low-acid ingredients such as vegetables or peppers, or relying on added acid to be safe rather than to set, can be a different kind of food in regulatory terms.

What to ask, and who to ask

This is a determination rather than a measurement, which means the answer comes from a person rather than a meter. Describe the product fully, including anything added for flavor, and ask the question plainly.

1. Is the product inside the standard of identity? If it meets the ratio and the soluble-solids figure, that is the first thing to establish.
2. Does it contain a low-acid ingredient? That is the question that most often moves a product.
3. Ask your state department of agriculture before the batch, not after. They answer this question routinely and we cannot answer it for you.

Measuring pH if you are

If the answer puts you inside the regime, the measurement becomes routine and the method matters. Strips are not adequate for a regulatory purpose and the meter needs calibrating against buffers rather than against memory. Calibrate at the start of a production day and record the reading alongside the batch number, because a measurement nobody wrote down is not evidence of anything later.

A calibrated meter, not paper. Paper strips are too coarse for a decision with a legal threshold in it, and the same calibration discipline applies as to a refractometer: an instrument that has drifted gives a confident wrong number.

References