Measuring pH properly

A pH meter that has not been calibrated today is an instrument reporting its own drift, and the number it gives you is the one your whole process rests on.

Why a meter and not strips

Paper strips resolve to perhaps half a pH unit and are read by eye against a color chart. The decision you are making sits at 4.6 and you are targeting well below it. Half a unit is the entire margin.

Strips are also poor on colored products, which a hot sauce always is. You are matching a color chart against a sample that is already red or green, and the error goes in whichever direction you were hoping for.

A meter with automatic temperature compensation and a replaceable probe is the tool. Expect to replace the probe periodically; they age whether or not you use them, and an old probe drifts slowly enough that you will not notice.

Calibrate every day you use it

Two-point calibration at pH 4.0 and 7.0 covers the range you work in. Use fresh buffer solution, not the bottle that has been open since last season, and rinse the probe with distilled water between buffers rather than wiping it.

Write the calibration down with the date. If a batch is ever questioned, the calibration record is what makes the batch record mean anything. A pH reading from an uncalibrated meter is not evidence.

Where in the batch to measure

Measure the equilibrated product, not the mix as you stir it. The acid needs time to distribute, and a thick or chunky sauce reaches equilibrium more slowly than a thin one. Your scheduled process will specify how long.

Take the sample at the temperature the process specifies, usually around 20 degrees Celsius, because pH is temperature dependent and a hot sample reads lower than the same product cooled. If your meter compensates automatically it will say so; if not, cool the sample.

Measure more than once from different parts of the batch. A single reading tells you about one spoonful. Pockets of low-acid material inside a thick sauce are exactly the failure the rules are written around, and an averaged reading hides them.

Recording it

Batch code, date, the reading, the temperature, the time since the acid went in, and which meter. That is the entry that makes the batch defensible, and it takes fifteen seconds at the bench and cannot be reconstructed afterwards.

Keep the strip of calibration records with the batch records. Inspectors ask for both, and producers who have one and not the other are in a worse position than producers who have neither, because it shows the process was understood and not followed.

References