I had a mug of packaged pudding. The top layer of the pudding was of typical pudding consistency, while the bottom was more runny. What could have caused this?
Starch makes a glue or a paste with water. Humidity from the air may be sufficient to transform your starch into a glue. Water produces strong hydrogen bridges between starch molecules. This transforms a pile of independent starch molecules into a strong block of interconnected starch molecules.