Freeze Stock

Chefs and other food waste-minding experts suggest saving vegetable scraps and peels in the freezer to make stock. This is a great way to use up vegetable scraps that would otherwise be thrown away.

Which Vegetables to Save

Yes

  • Onions of any kind, including shallots: skin, top, root end.
  • Scallions: anything you don't use.
  • Garlic: skin, any trim, germ (if you remove it).
  • Carrot: skin, root, tips.
  • Celery: any and all of it, although leaves are better put to use in soups and salads.
  • Turnip: any and all of it.
  • Fennel: in moderation, bulb and fronds.
  • Tomatoes: skin, seeds, flesh, pulp, tops.
  • Mushrooms: any and all of them, but particularly the stems.
  • More delicate herbs like parsley and thyme: stems and whatever’s on the verge of going bad. In moderation, woodsier herbs like rosemary or sage: again, stems and stuff that’s on the verge of going bad.
  • Ginger: peel and any trim.
  • Napa cabbage, but not any other cabbage: core and trim.
  • Leeks: root end and green tops.

No

  • Potatoes: these are better at soaking up flavors than imparting them.
  • Bitter and tender greens (e.g. broccoli, cauiflower): these overwhelm the stock to the point of making it bitter.
  • Peppers: they have too strong a flavor.

Maybe

These vegetables are fine to use, but can give the stock a particular flavor that may not be desirable depending on what you're making.

  • Lemongrass
  • Cilantro
  • Chinese celery
  • Daikon
  • Asparagus

For a long list of vegetables and their suitability for stock, see A-to-Z List of Vegetables to Include or Exclude from Vegetable Stock or Broth

How to Make the Stock

Because of the way the freezing process destroys the vegetables' cells, making stock with frozen vegetable scraps is a little different than using fresh vegetables, and is ultimately much more convenient.

That means covering frozen vegetables in water and cooking them for 20-40 minutes, which is what we call for in our quick and easy vegetable stock, is going too far. In fact, simmering frozen-then-thawed vegetable scraps for longer than 15 minutes produces an almost cloyingly sweet stock.

Vegetable Stock

To make a vegetable stock, place the contents of your freezer bag or whichever vegetables scraps in whatever ratios you’ve chosen in a pot, add a bay leaf if you want, cover everything with water, bring the water to a boil, reduce it to a simmer, and let it all cook for 10 minutes, and no longer. Strain it immediately through a fine-mesh strainer, ideally lined with some cheesecloth.

Chicken Stock

To use frozen vegetable scraps to make chicken stock (preferably from a stripped carcass): Simmer the carcass along with a bay leaf in water to cover for about three hours (one hour in a pressure cooker on high), then add the frozen vegetable scraps to the pot of chicken stock in the final 15 minutes of cooking. After adding the vegetables, crank the heat to bring the pot back up to a simmer, which should take about five minutes, and hold it there for 10 minutes. Strain it immediately through a fine-mesh strainer, once again ideally lined with some cheesecloth.

Sources: How to Cook With Wilted Vegetables and Prevent Food WasteSave Your Vegetable Scraps, Make StockA-to-Z List of Vegetables to Include or Exclude from Vegetable Stock or Broth