Food for shrimp generally comes in small packages so if you have a few tanks there is little chance of it going off before you use it all.
However if you only have one or two tanks or live along the coast (high humidity), one of the threats to the quality of your shrimp food is moisture. Moisture added to the food encourages the decomposition of the food and the growth of bacteria and fungi, which could potentially make your shrimp sick. One way to help keep your shrimp food in top condition is to use a silicon gel satchet that absorbs the moisture from the air in your container. Satchets are available online, but are also readily available as preservers in some human food items. Moreover the satchets can be recharged by drying them in an oven. If you are silly like me, and are constantly forgetting to dry your hands before dipping your fingers in the shrimp food, this may be a great way to protect the integrity and nutrition of your shrimp food.