How should I store the sachets after opening the box?

Keep the unopened sachets in a cool, dry place away from direct sunlight, heat and steam. A cupboard shelf away from the kettle, hob or radiator is usually better than an open counter or a spot above the cooker. The granules are dry and dissolve quickly in water, so moisture is the main thing to protect them from. If a sachet is already open, use its entire contents right away; once the granules are exposed to air or steam they can absorb moisture and clump.

Check the date printed on the package and the condition of the granules before use. If they look wet, heavily clumped or smell different than expected, discard that sachet. Keep the outer box closed when you are not taking out a sachet, and store it away from strong-smelling items, as dried herbs can pick up surrounding odours. This guidance is the usual common-sense handling for dry food granules; the details for a specific batch, such as the best-before date, are on the label.