Use bits and pieces of fresh vegetables which are usually discarded into a saucepan. These are carrot peelings, celery tops, cabbage cores, cauliflower stems, onion skins. mushroom stems, potato peelings, left-over undressed salad, etc. Put into a saucepan. Cover with cold water. Let simmer for at least 20 minutes. Turn off heat and let sit until cool. Strain and refrigerate until needed.