Checking the expiration date makes sense. I dump the food in a big air-tight container. I just read on this board that a big bag may go stale before you are through. How do I know if it's stale? Will my dogs not eat it? They aren't huge fans of plain dry dog food anyways.
So when I give them just DRy dog food, they sometimes won't eat it unless I mix something in. Now I don't know if it's because it's stale, or, if they are just waiting for me to mix something in. (yogurt, carrots, etc). !
My Puff (YF, AKC, field line, 63 lbs., dob: 8-'01) self regulates her food intake -- she's not a glutton like 90% of the other Labs.
She eats a total of 2½ cups/day of Kirkland C&R dry kibble. So a 40 lb. bag lasts some time and when it's unappetizing, she let's me know.
After trying a variety of containers, what works best for us (no loss of appeal or appetite) is to transfer the contents of a 40 lb. bag as soon as it's opened to 10-11 one gallon Ziplock freezer bags. 5 or 6 remain in the kitchen, the others rest in my freezer until the day before they're needed.
If you want a test on whether some opened dog food or dog food that you've stored in some container is still fresh, include with it some cookies or crackers when you put it there and then you can nibble a bite and taste it for yourself.