Have just been given a 5Kg bag of ' for baking' Castor Sugar. It's in a
paper bag, so I think it will go hard after a while, since it will be many
years before we can get through it.

How is it best to store it?

At the moment we are thinking of putting it in glass pickle jars with screw
lids.
Is there anything simple we could put in the jars with it, that would act as
a *drying agent* to take out any moisture for the air? Thanks for
advice.