Well I'm not that familiar with brewing ingredients yet, but when making cereal (crushing oats, roasting them and adding some cane sugar/honey/dried fruits they go stale REAL fast (I suspected the dried fruits).
So I cool them down slowly and put them in 3 liter vacuum jars. I found those for 2.99 each in January (they were 20 euro at christmas). They however sell larger ones.
They hold the cereal perfectly crisp and fresh for a solid 3 months, if stored in the dark. I believe vacuuming shredded grains would do the same.
The 7 liter ones are way overpriced and rather bulky though.
I'm not sure if anyone tried making vacuum bags? To keep the grain together just put them in a little ziplock bag with a couple of holes in them, before putting them in the seal pouch. The cheap, large sealers are often sold quite cheap over here (~40 euro).
A small note; obviously it really depends on how long you are planning to store them. The longer, the trickier it gets.