Extremes of humidity and washing aside, how about the damage dermestid
beetles and kin could do to a rice-paste creation? I'm sure most all of
us have come across the shed larval skins in our collections at one time
or another (all those "tails" left high in the spire to dry and become
odor-free are prime attractants). While dermestids are generally thought
of as dried animal matter eaters, they will eat through paper, plastic,
plant materials, etc.
 
Ken Zentzis
Wichita, Kansas