Sealing and induction

For a hygroscopic powder the closure is not a lid. It is the component that determines how long the product remains the product.

The seal is the shelf life

These formulations are mainly hygroscopic and are conventionally held in packaging from which humidity is excluded. The low moisture content is what gives a one to two year shelf life, because microorganisms cannot live without water.

So the moisture barrier is not packaging preference. It is the mechanism by which the product is stable and safe, which makes it a specification and makes a packaging change a reason to retest.

What each option does

A friction-fit or threaded lid alone is containment, not a barrier. Over months it will let a hygroscopic powder equilibrate with the room.

An induction seal bonds a foil membrane across the tub mouth, giving a genuine barrier plus visible tamper evidence. It needs a compatible liner, a clean flat rim and a sealing unit.

A foil-lined pouch with a good zip is an excellent barrier while sealed and a poorer one once opened, which suits single-serve and refill formats better than daily-use tubs.

A shrink band is tamper evidence and contributes nothing to barrier.

Desiccants

A desiccant sachet buys margin on the most hygroscopic formulas, absorbing the moisture that enters during repeated opening rather than preventing entry.

It is not a substitute for a seal and it has a finite capacity. Where it earns its place is a product opened daily for three months in a kitchen.

Getting the seal to take

Wipe the rim before sealing. Powder on the land is the commonest cause of an induction seal that does not bond, and a partially bonded seal looks sealed and is not.

Check a sample from each run by opening it, because a seal that failed is invisible until somebody tries.

References