I have been drinking more morning coffee lately, and noticed that although the first cup is fine, subsequent cups from the pot are somewhat bitter. I used to add a quarter teaspoon of demerara sugar to my cup overcome the bitterness, but sugar is now off my list. In reading about organic shade-grown coffees, I came across the suggestion of adding egg shells to the grounds while brewing.
Let me tell you, it makes a difference! Not in coffee taste, but in mellowness. (I drink either a French roast or a dark roast, depending on what my store has in stock.)
The alkaline calcium leached into the brew buffers the acids in coffee, and it adds some extra calcium to my system. The amount of acids in coffee vary by type of coffee maker, controlled by water temperature, speed of water seeping through the grounds, and to some extent by the type of roast of coffee itself.
So far I have just thrown a crushed shell in with the grounds, the more shell edge area, the better. Today I started putting the shells in a cloth re-useable tea bag, but I think I'm also going to pulverize the shells. I also read you could just drop a calcium supplement tablet in with the grounds.