It’s almost impossible to buy just a couple of ribs of celery, even though that’s usually all you
need. Instead, it comes in a massive bunch, leaving you to wonder what to do with the rest before it wilts in your crisper drawer. I found myself in this exact position one winter, after buying celery for soup and boldly declaring that I would waste less food in the new year. As I diced up the ribs I needed, I brainstormed ways to use the rest. Unsure exactly what to do with it, I settled on freezing it for mirepoix—the French term for the combination of onions, carrots, and celery—which forms the base for many braises, soups, and stews.
Many chefs I’ve spoken to advise against freezing fresh vegetables, since they can become mushy when cooked. But I decided to buck the advice of chefs and fellow food writers: I chopped up the remaining celery, along with some carrots and onions for good measure, and arranged them in a single layer on a baking sheet. Then, I popped them into my freezer. Once they were frozen, I froze each vegetable in its own zip-top bag.
A few weeks later, when a cold struck and I urgently needed chicken noodle soup, my frozen mirepoix came to the rescue. Instead of chopping vegetables, I simply reached into the freezer and pulled out the aromatics I needed, shaving 10 minutes off my prep time. Now, my freezer is rarely without a few bags of diced onions, carrots, and celery—and I’m always a few steps ahead when it’s time to throw together a weeknight dinner.
When I freeze mirepoix, I tend to chop up whatever onions, celery, and carrots I have left over after buying a bunch. If I’m feeling lazy, I break out the food processor and pulse each one to make quick work of it. (Just be careful not to turn them into a purée.) As I mentioned above, I separate the vegetables and arrange them in a single layer on a baking sheet. Once they’ve hardened slightly, about 15 minutes, I transfer them into zip-top freezer bags. I eyeball the amounts: Each bag contains about one medium onion, two carrots, or two to three stalks of celery. Knowing that each bag contains roughly the same amount helps me cook more precisely and makes it easier to adjust the ratio by supplementing with more fresh or frozen vegetables as needed. (You can, however, freeze each vegetable in its own bag if you prefer.)
Because I use this blend for mirepoix, many of the typical concerns about freezing produce and its effect on texture became moot. In mirepoix, the goal is to have the vegetables flavor the base of your dish, then practically melt into the background, so their texture isn’t as critical as it would be in something like a stir-fry. While prepackaged bags of frozen mirepoix are available, they are usually sold as a premixed blend, and I prefer to control the ratio of onions, carrots, and celery.
Mirepoix is primarily used in French cooking, but many other cultures have their own versions of aromatic vegetable bases. Italians call theirs battuto or soffritto, often including garlic, parsley, fennel, and pancetta or prosciutto. Most of my cooking leans toward the red-sauce variety, so I often add fennel to my stash of freezer vegetables as well. You can customize your freezer mirepoix blend as needed: Leeks, carrots, and celery root are used in German suppengrün, which literally translates to “soup green.” (I’ve also frozen both leeks and celery root for use in soups and stews, with much success.) For Spanish sofrito, you could freeze the onions, garlic, and bell peppers, then add the tomato during cooking.
When frozen this way, the vegetables can be stored for about three months—but as Meredith Carothers, a food safety specialist with the USDA, told me, that’s more a guideline for quality than for safety. When it’s time to cook, I don’t bother with thawing the veggies—and you shouldn’t either. As the vegetables thaw, ice crystals in the veggies melt and pool around them, making the onions, garlic, and celery mushy. Instead, I toss the frozen vegetables directly into hot oil in a pan. The extra liquid cooks off quickly, and the vegetables begin to brown just as they would if used fresh. From there, you’ve got the beginnings of a pot of soup, a hearty ragù, or a slow braise—minus the prep time.
