I think my aunt used to put clean broken egg shells into her coffee grounds (in the coffee maker) What exactly will this do?

From this website:



This is bit of folklore that has different rationales. Some old cookbooks claim that the eggshells help to clear the coffee by attracting floating grounds and then precipitating to the bottom; some of these old recipes call for adding an entire raw egg. Less commonly, adding eggshell to the grounds of coffee is said to take away some of the bitter taste that can be associated with coffee.

I'd never heard of this; I don't drink a lot of coffee so I'm hardly a coffee expert.

I heard this too. I think it may also lower the acidity as egg shell is high in calcium carbonate which would neutralize acid.

See what happens to egg shell when you put it in vinegar. I put a whole raw egg in a cup of vineage one time. The shell completely disappears and then you have a shelless egg.

It is important to keep THIS information in mind whenever using non-pasteurized eggs, regarding salmonella.

Even if the shell is cleaned after the egg inside has been used, I don't believe either that cleaning OR the hot water going through the grounds would be hot enough to kill salmonella.