Well, almost free.
I like to make my own broth for many reasons. It tastes better, I can choose how to salt it, it’s environmentally friendly, and it doesn’t sit on a shelf in plastic for an indeterminate amount of time before it arrives in my soup pot. But, let me be honest, the biggest reason I make my own broth (or stock, maybe, if you want to get technical) is that it’s irresistibly cheap.
Buying mostly organic produce is good for the environment and, I believe, for my family’s health. But the price tag still rankles a bit, especially here in Seattle where the only things that appear to grow effortlessly are rosemary and moss. Making my own broth allows me to essentially use my vegetables twice: I eat the trimmed part the first time around, and save the peelings for the stock pot. At $3.50 a quart, I’m saving over twenty dollars every time I make my own broth. If I do it once a month, the savings really add up over the course of a year. Of course, you might not eat as much soup as we do…but still. It makes me feel better about how much I pay for organic produce.
[UPDATE: Many of the comments below mention composting veggie scraps or feeding them to the chickens. This, of course, is their third and final use after you have boiled them for stock!]
The basic method is to chop your selected organic vegetable trimmings into 1-2” pieces and save them in a bag in your freezer. (I wouldn’t do this with non-organic vegetables, because I’d be concerned about concentrating the pesticides that are in the peels. This is my completely unscientific personal opinion.) Add to the bag over time. When it’s full, put everything in a pot, cover it with water, add some seasonings, and simmer for 30-45 minutes. Add salt until it tastes like something you’d like to drink by the mug. Strain and use your broth, or freeze it for later use. Get a new freezer bag of trimmings started and repeat.
The only mental effort required is the contemplation of whether the trimmings you have before you will taste good in your broth. Some are easy: Carrots? Yes. Broccoli rabe? Probably not. Turnips? Trick question! They’re great.
You want to aim for a balance of flavors in your stock pot. For me, the essentials are onion, celery, and carrots (or another sweet vegetable, like winter squash). If I don’t have some of each in my frozen mix, I will sacrifice a whole onion or a few stalks of celery to balance out the flavors. Beyond, that, though, the sky’s the limit. I have tried to list some of my favorites (and a few un-favorites) below, but if you want an opinion from me and/or your fellow readers about whether a particular vegetable would be good in a broth, please just ask in the comments.
One more note: this process has the added benefit of giving you seasonally-flavored broths. The vegetables I’m cooking this month are going into the freezer, and what goes into the freezer ends up in the stock, which means that my stocks reflect current seasonal flavors. Perfect, because my soups usually do as well. It’s a beautiful cycle. When cooking in the summer, I usually do want a light broth with corn and tomato flavors, and in winter I am glad to have a rich one full of mushrooms, root vegetables, and winter squash.
Homemade Vegetable Broth: I usually wait to make broth until I have two gallon bags full of frozen vegetable trimmings, which I dump into my huge stock pot and cover with 8 quarts of water. I add 2 Tb. salt, a small handful each of dried bay leaves and peppercorns, and several branches of parsley and/or thyme if those stems weren’t already in the mix. Peer into your pot and consider the flavor balance; add a chopped onion, celery branch, or carrot if needed. Bring to a boil, reduce heat (consider adding a Parmesan rind now for a deeper flavor if you have one handy) and simmer 30-45 minutes, until the flavor of the broth is well-developed. Add additional salt to taste. Strain and freeze. I usually freeze some in quarts and some in pints, and I sometimes also wish that I had frozen some in ice cube trays, but I never do. (These quantities yield 6-7 quarts of broth.)
Always good (only use unspoiled vegetables and trimmings without bad spots):
Root vegetable peels (including potatoes)
Alliums (tops and trimmings from onions, leeks, garlic, scallions)
Apple and pear cores (just a few, can replace carrots for sweetness)
Herb stems, especially parsley, oregano, thyme, bay
Winter and summer squash (including seeds and peels of winter squash)
Beet greens, spinach, chard, and chard stems
Corn cobs (cut to 2” lengths)
Tomato cores and peels
Green bean tops and tails
Not so good:
Brassicas (kale, broccoli; cabbage is ok in small amounts)
Chicories (radicchio, dandelion)
Beets (unless you want a very pink soup; golden beets are ok in small amounts but they’re very sweet)
Anything with a very strong flavor (see the first comment below about inadvertently making a pickle brine broth from dill stems)
And finally: After making this list, I went to consult my vegetable bible, Deborah Madison’s Vegetarian Cooking for Everyone, and I saw that she has a similar but much more detailed list of vegetables that she recommends using and/or avoiding. And our lists are not the same. So experiment! And, as always, consider your own tastebuds as you curate your frozen vegetable scrap collection.