My mum has always said no more than a few months opened. I buy bulk too and try to get as much of the air out as I can when I seal it up. The bottom bit always seems to end up in cookies and the sugar seems to off set whatever may be a bit out dated.
I love the tall stackable tupperware containers for bulk staples!
"Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence."