Particularly for a clear soup, it's advisable to remove any fat and other impurities from the stock, so that you end up with a crystal-clear liquid.
To Clarify Stock: To clarify 1 quart of stock, you will need 2 Egg Whites and 1 Crushed Egg Shell. Whisk the whites and add to the stock with the crushed shell. Bring stock to a very gentle simmer and leave for 20-30 minutes: the sediments will attach themselves to the egg whites and a thick scum will rise to the surface. Remove the pot from the heat and leave to stand for 15-20 minutes. Now simply push the scum aside and ladle the stock through a sieve lined with a damp cloth (thick cheesecloth). Allow to cool, then refrigerate or freeze until needed.