Preservative failure

The failure with the worst customer photograph, and the one most likely to be under-dosed rather than absent.

What it looks like

Cloudiness, then a smell, then a film, a slime or visible mold.

Viscosity loss, as a thickener is broken down.

Gas in a sealed bottle, which shows as a swollen container.

Any of them in a cleaning product is alarming to a customer in a way it would not be in a food, because the product is supposed to be the clean thing.

Why it fails

Under-dosed. The commonest cause. Somebody used the bottom of the range, or reduced it because the raw material is expensive, and the product survives the shelf and fails in a cupboard.

Wrong pH. Most preservatives work in a band, and a formula outside it has an ingredient doing nothing.

Deactivated by a surfactant, by free metal ions, or by a plastic container absorbing it, which several preservatives do.

Overwhelmed by the input: contaminated water, dirty equipment, or a raw material that arrived with a load.

Reinoculated in use, by a refill bottle topped up rather than emptied.

The one that is not visible

A contaminated product can look and smell entirely normal.

Which is why the only real test is a challenge test: deliberately inoculating the formula and measuring whether the preservative controls it.

It is a laboratory test, it is not expensive relative to a recall, and it is what a wholesale buyer will eventually ask about.

Preventing it

Deionized water, clean equipment, and a sanitized filling line.

The supplier's recommended level, not the bottom of the range.

A chelator, which improves efficacy.

pH inside the preservative's working range, checked on every batch.

And retained samples kept and looked at, so a slow failure is caught in your cupboard rather than somebody else's.

References