I'm not sure. I don't usually rinse the shells, I have a small plastic takeaway bowl that I toss the shells in when I use eggs. They usually dry out overnight. There might be some leftover egg white in the shell, but not much. Then I just toss them into the mortar and when I have some time, I just grind the shells and pour into a bag. The coffee grinds (don't have often as I don't drink a lot of coffee, but I do get them... I also mix tea grinds as well) need to be dried as well. Then starting in the spring, I have plenty of material... I just mix in handfuls of what I have, then sprinkle in the garden and the lawn. The lawn doesn't like it as much, but this usually gives me some pretty nice tomatoes and lots of raspberries.

One thing about the tea and coffee grinds... when you're drying them out, you have to spread them out and I would recommend setting out a fruit fly trap nearby. Doesn't happen often, but occasionally you get large numbers of fruit flies.