Net weight drifting between tubs

A supplement tub carries two quantitative claims, and a fill that drifts breaks both of them at once.

Two claims on one container

The net quantity of contents, which is a weight. And the servings per container, which is derived from that weight divided by the serving size.

So an underfilled tub is short on net weight and delivers fewer servings than the panel says. One error, two false statements.

Why powders are hard to fill

Low bulk density means a large, airy, variable volume for a given mass. Fine powders carry static and cling. Cohesive powders bridge in a hopper and deliver inconsistently.

And bulk density itself moves: with particle size, with moisture uptake, and with how compacted the source container was when the run started.

What drifts through a run

The source hopper compacts as it empties, so later fills come from denser material. Moisture uptake increases as the batch sits open. And if the blend is segregating in the hopper, later units differ in composition as well as in weight.

Which is why sampling the first unit and calling the run good is not sufficient. The end of a run is where the drift lives.

Controlling it

Fill to weight, with a scale, never to a volume mark. Set the target slightly above the declared quantity, because the distribution has two tails and only the low one is a compliance problem.

Check-weigh from the start, middle and end of every run and record all three. A trend across those three is the fill drifting; a spread is the powder varying.

And re-establish the target whenever the formula, grind or flavor system changes, because all three move bulk density and the previous setting is now wrong.

References