The Best (& Worst) Leftover Veggies To Add To Boxed Stock
Boxed stock remains a practical necessity in the world of home cooking. It's a soup season savior, a quick fix for holiday meal planning chaos, and a sick day alternative to ordering in a $20 bowl of ramen.
But it's a known fact that boxed stock simply doesn't taste as good as the stuff your grandma used to spend eight hours hunched over the stove making. Homemade stock is thick and golden, jam-packed with nutrients, various aromatics, and (unless you're vegan) collagen that's extracted from animal bones, and is made with many hours of simmering until the product reaches the status chefs refer to as "liquid gold."
If you don't have the time or the inclination to make your own stock, however, there are some things you can do to take your humble carton of broth from bland to bellissima. Cooking down vegetable scraps you have lying around and then adding the stock, so your leftovers flavor it to perfection, is an easy way to transform boxed stock, as long as you make sure you're adding the right vegetables. But don't go rummaging in your crisper drawer before you know just what to look for.
What veggies to toss in and leave out
If you've ever made soup from scratch, you probably already have a rudimentary instinct for what flavors go well in stock. Aromatics like garlic, onions, leeks, bell peppers, carrots, celery, fennel, lemon grass, ginger, or scallions bring flavor and depth to a bought stock. If you are working with a flavor palate from a particular country or region, look to see what aromatics are used in different locales. For a pot-au-feu, try a mix of onion, carrot, and celery for a French mirepoix, perhaps perked up with some leeks. If going in a Cajun direction, the Creole "holy trinity" of onion, celery, and green bell pepper would be more appropriate. Dried or fresh mushrooms can add, meaty, umami flavors to stock, particularly shiitake mushrooms, which pair well with kombu seaweed for a Japanese-style dashi broth.
Not all vegetables are fit for stock, however. Cruciferous vegetables like brussels sprouts, cabbage, broccoli, cauliflower, and kale contain high amounts of sulfur, which will overpower your broth and make it extremely bitter. Other veggies to avoid are the skins of squash or zucchini, the leafy ends of carrots and celery, and green beans, which turn bitter when cooked for periods. And while root vegetables like potatoes or turnips are great in soup, they are not built for stock foundations, as their starchiness will cloud and thicken the stock.