Found this info from: http://www.wheyproteinking.com/whey-protei
Does Whey Protein Have an expiry Date?
All whey protein products have a printed expiration date on the label or container. People have complained of severe stomach upset and other illness from taking out of date powder, this is most likely due to breakdown of the excipients in whey protein powder, such as colorings and flavors. The whey powder itself is usually dated from a couple of years after manufacture and after this, the nutritional values cannot be guaranteed as still being accurate. For these reasons, the expiration date should be adhered to.