I know that this may seem like a silly question to answer, and it is a personal one. Even spraying nonstick cooking spray in the jars, the baked-on egg whites can be difficult to get clean. You can't just pop them in the dishwasher - they will not get cleaned that way. I have found it best to spray some Dawn Powerspray * in them and let them sit for 30 seconds. Then scrub out with a scrubber with warm water. The Dawn Power Spray helps lift the baked-on eggs really well and it is the easiest way to clean the jars fully I have found!