Eggshells help reduce acidity in coffee due to the presence of calcium carbonate in the shells, which also improves the taste for those who prefer a less-acidic coffee. It also helps a coffee drinker with a stomach sensitive to acidity levels in coffee or who has medical problems such as acid reflux.
Many people find that coffee has a bitter taste. However, putting eggshells in the pot of coffee can reduce that bitter taste, allowing users to enjoy the other benefits of coffee, such as the caffeine, without the aftertaste.
The presence of eggshells can also help settle coffee grounds to the bottom of the coffee pot so that they don't float up and into the coffee. This tactic is used more often when brewing coffee in a percolator, campground or another type of brewing pot.
How to Do It
Do not place raw eggshells in a pot of brewing coffee, as this increases possible exposure to such contaminants as salmonella or E. coli. Bake the eggshells at 350 degrees Fahrenheit for 10 minutes. Crush when cool and place in a sealable bag to store. Add 1 tsp. of eggshells to coffee grounds before brewing.