What goes wrong

The pH was measured wrong

Updated October 2026

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Equilibrium is the word that matters Measuring the liquid is not measuring the product Temperature affects the reading Paper is not a measurement here And a recipe that worked is not evidence Water activity needs its own instrument Getting it wrong goes one way The error has a direction, which is why the method matters References

4.6 is close to ordinary food, so a sloppy measurement is the difference between two regimes.

Equilibrium is the word that matters

The definition says finished equilibrium pH. That is the figure after solids and liquid have reached the same acidity, which for a chunky product can take considerably longer than a production day.

Measuring the liquid is not measuring the product

A dressing or brine can be well under 4.6 while the center of a vegetable piece in it is still above. The piece is part of the food and the equilibrium figure is what governs.

Temperature affects the reading

A meter reads differently on a hot sample, and the figure that matters is on the finished settled product at a controlled temperature. Measuring off the stove is convenient and wrong.

Paper is not a measurement here

Litmus or test strips resolve far too coarsely for a decision at 4.6. A calibrated meter, calibrated that day against standards, is the only instrument that answers this question.

And a recipe that worked is not evidence

Ingredient acidity varies by season, variety and supplier, so the same recipe produces a different pH batch to batch. The measurement is per batch, which is why pH records exist.

Water activity needs its own instrument

And it is the second half of the definition. For a soup or broth it will be well above 0.85 and is not a realistic route out, but for a thick reduced or very salty product it is worth measuring rather than assuming.

Getting it wrong goes one way

Believing you are acidified when you are low-acid means a shelf-stable product made outside the regime that governs it. The error has a direction, and that is why the margin and the method matter.

The error has a direction, which is why the method matters

Believing you are acidified when you are not produces a shelf-stable low-acid food made outside its regime. The opposite error only costs you an unnecessary process. Asymmetric risks deserve asymmetric caution.

References

21 CFR 113.3, the definitions for thermally processed low-acid foods packaged in hermetically sealed containers. Paragraph (j) defines a hermetically sealed container as one designed and intended to be secure against the entry of microorganisms so as to maintain commercial sterility; (n) defines low-acid foods as those with a finished equilibrium pH greater than 4.6 and a water activity greater than 0.85, excluding tomatoes and tomato products below pH 4.7; (r) requires a scheduled process at least equivalent to one established by a competent processing authority. law.cornell.edu

21 CFR part 114, Acidified foods, the regime for foods to which acid or acid foods are added to produce a finished equilibrium pH of 4.6 or below, which is the alternative route for a product that would otherwise be low-acid. law.cornell.edu

Written from federal regulation, not from a production kitchen. Nothing here is a scheduled process, and nothing here is a substitute for a competent processing authority. If you are considering a shelf-stable low-acid product, the first call is to a process authority rather than to a packaging supplier.