Vacuum Packed: How Long?
Don't know about grains but I can tell you I'm still using vacuum packed yeast from my freezer that supposedly expired more than a year ago.
I also had a sauerbraten that was vacuum packed and frozen for more than a year. It was excellent.
Not much can happen in the absence of air and moisture. I use the freezer for back up but I think it's the absence of air and water that ensure the freshness. You might just find you have to cook your risotto a little longer. Don't watch the clock; taste your rice for the texture you want.