While sugar doesn't really expire, per se, if kept too long or
in a non-airtight container where humidity can get in, it WILL
become a solid, unreasonable block. Sugar is an incredible
preservative, working in jams, jellies, and twinkies (which
apparently also never expire, lol)
If your sugar does form into a block, a good way to get around
this is by dissolving it in a small amount of liquid, and air
drying in a thin layer on a baking sheet at room temperature
(drying in the oven can cause carmellization, which affects taste
and color.) You can also try nuking it for a very short time in the
microwave, but I don't prefer or recommend this method as it may
unintentionally scorch the sugar.