Humidity (moisture) and air eventually move through most plastics.
These Tang containers are made of HDPE (high density polyethylene) plastic, the same plastic that buckets are made of. The one on the left has been stored unopened but was stored long past the “use by” date. Humidity (moisture) and air have migrated through the plastic causing the powder to darken and to stick together in one mass. The one on the right is a new container for comparison.
HDPE plastic is not air proof, oxygen proof, or moisture proof. For long-term storage (more than 5 years), foods need to be packaged in metal, PETE (polyethylene terephthalate) plastic, glass, or mylar or the atmosphere needs to be replaced by a gas that is a larger molecule such as carbon dioxide. That can be accomplished in HDPE buckets by using dry ice, which is frozen carbon dioxide.
For instructions on how to use dry ice in HDPE buckets, see “Dry Ice Treatment in Plastic Buckets” on simplyprepared.com.
