Mushroom-extracts are spray dried and therefore very hydrophilic (deutsch!), in other words they strongly draw humidity out of the air. The most sensitive thereby is the maitake-extract. Thus, capsules with mushroom-extract must not be standing open to the air. Cans with mushroom-extract capsules should be consumed within 3 months after opening (Maitake possibly even within 2 months!)
Generally mushroom powders and mushroom-extracts should be stored in a cool and dry place protected against sunlight.