How should I store the pastille after opening to keep it fresh?

Specific storage instructions usually appear on the package, so check the label first. For a fruit-based pastille like this, the main things to avoid are heat, direct sunlight, and high humidity. Stored in a cool, dry cupboard, the product keeps its soft, dense texture better.

After opening, reseal the package as well as you can or transfer the pastille to an airtight container. This stops it from drying out and becoming hard, and also prevents moisture from making the surface sticky. You do not need to keep it in the refrigerator, and doing so can sometimes introduce condensation when the package is opened. Keep it away from strong-smelling foods, because fruit snacks can absorb odors.

Like all foods, use the best-before date as a guide. If the pastille smells sour, shows mold, or has an off texture, throw it out instead of eating it.