The challenge test, and what it costs

The challenge test is the difference between believing your product is preserved and knowing it. It is also the expense most new brands try hardest to avoid.

What the test actually does

It deliberately contaminates your finished product and watches whether the preservation system kills what was introduced. The standard method in the United States is USP <51>, Antimicrobial Effectiveness Testing.

It translates a theoretical design, your water activity and preservative and pH and package, into evidence that the product will not become a microbial problem once it is out of your hands.

Five organisms, twenty-eight days

The formula is inoculated separately with five organisms spanning gram-negative and gram-positive bacteria, yeast and mold. They are chosen to represent the contaminants that actually arrive: from manufacturing, from clinical environments, and from a household bathroom.

Counts are taken at days 0, 2, 7, 14 and 28. A passing system reduces the populations on a defined schedule rather than merely holding them steady.

So the answer takes a month. That timing has to be in your launch plan, not discovered after you have ordered packaging.

What it costs and when to run it

A few hundred dollars per formula at a contract laboratory, which feels enormous against a first batch and is trivial against a recall or an injured customer.

Run it on the final formula in the final package. A test on a beaker sample tells you less than you think, because the package is part of the system being tested.

What a pass does and does not mean

It means the system worked against those organisms, in that formula, in that package, at that time. It does not license a changed formula, a changed supplier of a key raw material, a changed package, or a changed pH.

And it is not a safety substantiation on its own. Preservation is one part of the assessment, and the assessment is the obligation that has no small-business exemption.

References