Equilibrium pH, and the number 4.6

What equilibrium means here

When vegetables go into an acid brine the two do not stay separate. Acid moves into the vegetable and water moves out, and the whole jar converges on a single pH over hours or days. That final, settled figure is the equilibrium pH, and it is the one the definition is written about.

It is almost never the pH of the brine you mixed. A brine well under 4.6 can equalize to a finished product above it, because the vegetable brought its own, much less acidic, water to the jar. This is the single most common way a maker holds a confident number that was never true of the product.

Why 4.6

It is the threshold in the federal definition of an acidified food, which is a low-acid food to which acid is added to reach a finished equilibrium pH at or below that figure, with a water activity above 0.85. A pickled vegetable is the paradigm case. Below the threshold the product sits in a regime with a filed process behind it; the whole commercial shape of this business follows from being inside it.

Measuring it properly

On a settled jar, at room temperature, with a calibrated meter. Not warm, not on packing day, not by taste. Those conditions are not fussiness: a reading taken outside them is a number about a moment rather than about the product, and it is the number your whole position rests on.

Your figure comes from your process authority

The 4.6 threshold is the definition. The number YOUR product is built to hit, with whatever margin your process specifies, comes from the authority who established the process for your formulation. Work to that one.

References