I just threw out a package of natto with a Dec. expiration date and consumed one with a Feb. date which seemed fine. How important are natto expiration dates? What risks does post-dated natto carry that current natto does not? I don't understand the significance of the expiration date of a fermented product such as natto. I have the same problem with yoghourt. I am not a beer drinker but don't recall seeing such dates on beer. What about kimchee and other pickles?