A whole lot of soup is cooked around here so stock is a definite pantry staple. In an effort to waste less, when preparing a meal, clean veggie trimmings are saved in gallon sized ziplock bags in the freezer. This includes onion bits, mushroom stems, green leek leaves, carrot peels, celery stems... When the bag is full, I make vegetable stock. When we roast a chicken , the bones go in a freezer bag of their own and is used with a vegetable bag for chicken stock.
It's easy to do and the time it takes is largely unattended. Remove full vegetable bag from freezer, and chicken if using, empty contents into very large stock pot, cover with water by a couple inches (about 16 cups) and consider adding the following:
-whole black peppercorns
-any aromatic herbs or seeds
Bring to a boil and reduce heat. Simmer, partially covered 4 - 6 hours, skimming off any foam that forms of the surface. Set a strainer lined with cheese cloth over another pot and carefully pour out all the stock and bits, pressing down on the vegetables, squeezing out all liquids. Discard cheese cloth and solids. Stock may now be used or frozen.
If freezing, let stock cool completely. Consider using lidded plastic pint container (they stack easily) and only fill 1 inch from the top to allow for expansion when freezing. Also, labeling helps too.
Makes about 14 cups.