If you have an extra plastic bag and use fresh vegetables from time to time you can always be just a few minutes away from fresh vegetable soup stock.
I like to use a zipper bag with the easy-closure type zipper because it will need to be opened and closed a number of times, but any bag at all would do.
Whenever you clean fresh vegetables, put the raw pieces that aren’t good enough for serving into the plastic bag. This can be almost any kind of vegetables with a few exceptions: Don’t put too many cabbage relatives in the bag, or the stock will have a very strong cabbage flavor. Of course, if you don’t mind this it’s not a problem. Vegetables that might be too strong are cabbage, kale, cauliflower, or Brussel sprouts. I have used broccoli without any problem.
Just toss in most of the stuff that you might otherwise throw away. This is certainly not an exhaustive list, but it includes the things we use most commonly here. I’ve used:
carrot ends and peels
the celery butt with the last tiny bit cut off so that I can wash out the grit
green bean ends
onion ends and outer leaves that aren’t too papery
spinach stems and leaves that aren’t really rotten, but don’t look great to serve any more
fibers and ends from bell peppers- green, red, yellow
Keep the bag in the freezer. Fold the top over and push as much air out as possible when you close it each time. When the bag is full- or half full... this is a very inexact “recipe”... throw the veggies in some cold water and bring it to a boil. How much water? Depends on your quantity of veggies. If the bag is nearly full I can easily make 6-8 cups of stock. If the bag is not full it might make a little less. The stock can always be extended or amended with a bullion cube. (Although, since hubby now needs to cut out salt, we don’t do this.)
When it comes to a boil, reduce heat to simmer and cook for maybe 30 minutes. Drain the liquid, which is what you want to keep, so not into the sink. Duh! The cooked vegetable scraps are now ready for the compost pile.
If you feel that the stock has collected some extra grit from the vegetable ends you can always strain it through a fine sieve or some cheesecloth. You can even just carefully decant it and throw away the dregs which is what I do if it seems to need it.
The color of your stock will always be a crap shoot. It can be anything from dark green to gray, but the taste is good as the base for most any soup and is likely to end up being colored by whatever are the main ingredients in your final recipe.
This is full of the vitamins and minerals that were in the veggies, rather than just flavored salty water from a bullion cube.