Save Your Vegetable Scraps, Make Stock

You've likely heard this kitchen tip before. But we've thought through all the factors in great detail.

Overhead view of a pressure cooker filled with vegetable scraps.

Serious Eats / Sho Spaeth

I am going to try to convince you to save your vegetable scraps to make stock.

This isn’t some life-changing tip that’ll make your cooking better by leaps and bounds. It isn’t some hack that’ll save you time, or “blow your mind,” or reorder your understanding of how to prepare food for yourself at home. It isn’t even particularly convenient, and the reward isn’t as clear cut as adding fish sauce to chili or salting your steaks an hour before throwing them on the grill. It isn’t even something that Serious Eats can get 100% behind as an editorial recommendation, like reverse-searing roasts, or spatchcocking chickens, or using baking powder to assist with achieving crispier cooked poultry skin, because it isn’t really a hard and fast rule that everyone on staff observes with any kind of regularity.

Rather, it is something I do and have done for a very long time, mostly because I am (sometimes) frugal to the point of absurdity. But I believe that many of our readers might find this practice useful, particularly as it seems that more people are cooking at home more of the time, especially after living through an extended pandemic. And while the bottom line is pretty self-explanatory—save your scraps, use them for stock—I have over the years devised a kind of system for using them, which has in turn produced a kind of light philosophy about cooking, and some of you may find an explanation of both useful or instructive.

Or maybe not; if the idea doesn’t appeal to you, you needn’t read on, because, again, the lesson here is simple: Save all the detritus produced by chopping vegetables, put it in a freezer bag (which you should reuse) in your freezer, and when you have an ample amount, use them to make some kind of stock.

Why You Should Save Vegetable Scraps for Stock

No matter what you cook, you’re likely to produce waste, even if it’s just the garlic skins from a few cloves you’ve minced for aglio e olio. If you cook more frequently, or if you’re cooking large quantities, whether it’s for a dinner party or because you’re meal-planning for a week, you end up with a lot of waste: the root ends of onions, along with their severed tops and discarded skins; the tip and tail of a carrot, along with its peelings; the white root ends of celery, perhaps the leafy tops, and, if you’re diligent about such things, the stringy exterior of the stalks; scallion butts, and any of their ratty trim; herb stems; etc. The list is as endless as the list of stuff you’ve chopped.

Of course, all of that isn’t necessarily waste; a lot of it is in fact quite flavorful, and therefore doesn't have to be waste at all. The best part of a carrot, like many other roots and tubers, is its skin; the root end of an onion is just as flavorful as its middle, if a little more difficult to cut up; and while it’s uncommon in Western kitchens to use and eat the skins of garlic, it is common in other cuisines, as in Thai cuisine, to include garlic cloves, skin and all, in aromatic pastes. The only reason one might view the stuff typically left on their cutting board as waste is either because of ignorance about how to use it, or out of convenience; it’s much easier to slide that stuff in the trash than to figure out how to use it for some other, palatable purpose.

Except it’s very easy to use those things: throw them in a pot, either along with a chicken carcass or just on their own, cover them with water, and simmer them for a while. Strain the liquid through a fine mesh strainer, and what you’ve got is a flavorful stock that can be used as a base for a soup or a sauce, or even a liquid medium for a braise.

Two freezer bags filled with vegetable scraps on a sheet pan

Serious Eats / Sho Spaeth

Of course, that’s easier said than done. If you read cookbooks or recipe websites with any regularity you’ll know that you can do this, since it is often suggested, although typically only in passing; you may even have seriously considered it once or twice. But the immediate problem I encountered when I decided to try to do this regularly is that even if you cook quite a lot—say, you cook one meal every night, from scratch—the amount of scraps you produce is minuscule, at best. Let’s say you chop up an onion every one of those nights, and you throw in a few carrots and a couple stalks of celery for good measure, maybe a bulb of fennel, too; at the end of the week you’d have barely enough vegetal matter to produce a half cup of stock—onion ends and skins, a few peelings of carrot, all the stuff you can’t figure out how to cut cleanly from the fennel. It’s not enough.

Which is why you should turn to the freezer. If you make it a point to squirrel away whatever vegetable odds and ends you produce everyday in a ziptop freezer bag in the freezer, in a couple of weeks you’ll have more than enough stuff to make a fair amount of stock, and the stuff will keep for however long it takes before you have the time and leisure to make a pot of stock. As you can see from the photo above, there are two bags filled to bursting with a variety of scraps, each of which weighs around 800 grams (roughly two pounds), which is sufficient to produce about four cups of weak stock.

There are two distinct benefits to doing this, as I see it. The first, and most important, is cost efficiency. The second is a little less tangible, but it’s nevertheless a significant part of the appeal: you don’t have to be as fussy when chopping vegetables.

"This is also a great way to hold onto and use vegetables that are slowly rotting in your vegetable drawer."

The cost efficiency of using all of a vegetable, rather than just part of it, should be self-evident. If you pay a dollar for a carrot, say, and you peel it, trim the top and the sprouting end, then chop it up for a stew, the peel and the trim represent about 10 cents of your purchase, and if you don’t save them for another use, you’re essentially putting 10 cents in the trash. This is also a great way to hold onto and use vegetables that are slowly rotting in your vegetable drawer. That head of celery that’s on its last legs? Break it up and stash it in a freezer bag for when you need it.

There's another part to the cost-efficiency benefits, of course, and it’s that, by turning scraps into stock, you obviate the necessity of spending more money on ingredients for stock or boxes of pre-made stock.

Once you’re committed to saving scraps for stock, the other benefit reveals itself: You don’t have to be as diligent about the way you cut up vegetables. If you know that whatever’s left of the onion you’re chopping for a stew is going to end up in a stock pot, you don’t have to use up as much as possible of the onion in question (to get your money’s worth or to prevent wastage, whichever way you want to look at it). Therefore, as you slice closer to the root end, which typically takes a bit more care and attention, you can just leave off whenever you wish, secure in the knowledge that you’ll end up using whatever you don’t cut.

This can help speed up your vegetable prep time immensely, and can also help with safety, especially if you’re dicing hard vegetables like carrots and want to be a perfectionist about making every little cube perfect. Let’s say you want to dice a few carrots for a lentil salad: instead of peeling the carrot and placing the cylindrical root on your cutting board and trying to produce a uniform series of cubes, you can cut the cylinder into a rectangle, saving the rounded sides for stock. This provides you with a flat, stable edge on every side that can more easily and quickly be cut into planks, then strips, then, crosswise, into a consistent dice.

How to Save Vegetable Scraps for Stock

Frozen vegetable scraps unbagged and placed on a sheet pan

Serious Eats / Sho Spaeth

While you can use a lot of vegetables in stock, you can’t use all of them, because some vegetables—particularly cruciferous ones like broccoli and cauliflower—will make your stock bitter or otherwise unpalatable (read: farty). Here, then, is a small list of commonly used vegetables that are perfect for this purpose. The one thing to keep in mind is all your vegetables and scraps should be free of rot and dirt, so while you certainly can include onion skins, discard onion skins with dirt caked onto them, and shave off the root end of the onion if it’s particularly dirty. In other words, wash your vegetables, people!

Vegetable Scraps You Should Freeze for Stock

  • 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.

Bitter and tender greens should generally be avoided, along with things like peppers, which have a flavor that can overwhelm a general purpose stock, and potatoes, which are better at soaking up flavor than releasing it. However, there are some aromatic vegetables and herbs that are perfectly acceptable to save and use in stock, but you may not always want to use them every time; things like lemongrass and cilantro, which can lend the stock a particular flavor profile, perfect for some applications, incongruent in others. The way I get around this is I have multiple bags of frozen scraps in my freezer, one for general purpose vegetables like onions and carrots, another for more niche produce, like the ends of flowering garlic chives, Chinese celery trimmings, daikon, and the like.

I’ve found it best to only ever take out the bag(s) in the freezer when I’m ready to add to it and can immediately replace it, so as to avoid accidentally thawing the contents of the bag. Stored in this way, the vegetable scraps remain identifiable and can be easily disentangled. If you don’t do this, what happens is that the vegetables will turn to mush when they thaw, as the freezing process completely destroys the cell barriers in the vegetables. If you subsequently freeze that mush, it forms a solid block of frozen mush, which can be incredibly inconvenient if you are rooting through the bag for specific vegetables, as when I hunt for unused half carrots to throw into pots of beans, for example.

How to Use Frozen Vegetable Scraps to Make Stock

Frozen vegetable scraps in a large pot

Serious Eats / Sho Spaeth

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.

As Kenji explains in his tip about freezing aromatic vegetables before pulverizing them into a paste, a lot of the flavor (and water) in the vegetables is immediately accessible if they’ve been frozen and thawed. 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.

Sweetness is really the main pitfall of this method, particularly if you don’t pay attention to the composition of vegetables you add to the pot. On most Sundays, I’ll just use everything that’s in the bag to make a stock of some kind, and the results are mixed; some weeks, when I’ve mostly made stuff that required only onions, carrots, and celery, in relatively equal proportions, the stock is perfectly fine; on others, when I’ve happened to cook a lot of turnips, the stock will be so sweet that it’s almost unusable, and the same will happen if you use a bag that’s just filled with onion scraps.

Given that this method is more about cost effectiveness than flavor, it’s up to you how diligent you are about balancing out the ratios of the vegetables in the 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.

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.

Keep in mind that because the vegetable scraps will consist primarily of skins and peels, adding them to a pot of simmering water will immediately stain the broth a dark caramel color, which may or may not be important to you, depending on your aesthetic preferences. For example, a risotto alla milanese made with this stock will take on a muddy brown hue (don't do that).

How to Use Stock Made From Vegetable Scraps

A stock made with frozen vegetable scraps isn’t by any means a beautiful stock, and if you're only using vegetables and aren't adding anything with collagen (meat, basically), it will have no gelatin in it, which means it will lack body and, as a result, will never thicken, no matter how much you reduce it. (If you must use an only-vegetable stock in an application that requires gelatin's thickening power, you can add it directly, just as with store-bought stock.)

This stock also isn’t meant to be a replacement for well-made stocks, like the kinds we have recipes for on the site, like our hearty vegan vegetable stock, our brown chicken stock, or our white chicken stock (which, if you make them, will produce a fair amount of vegetable scraps; save those!). It can be used as a substitute, although it’s decidedly inferior. As such, while it can be used to boil beans, braise meats, make a pan sauce, or poach some fish, it isn’t particularly useful if you’re looking for clean flavors and a clear appearance, as with chicken noodle soup or ramen. It is, however, a very good way to add more flavor to grains like freekeh, farro, or rice.

It’s best to think of these stocks as a supplement, not a replacement, to more meticulously made stocks; they are, in effect, a replacement for inferior store-bought stocks, made with stuff you were going to throw away anyway, a way of getting the most you can out of what you’re already purchasing.

June 2020