Can You Freeze Chopped Onion, Carrot and Celery? What to Blanch First

Key Takeaways:

• Diced onions go into the freezer raw. The National Center for Home Food Preservation (NCHFP) says no blanching is required.
• Diced carrots need a 2-minute water blanch, and celery cut into 1-inch lengths needs 3 minutes, per NCHFP.
• Frozen celery works only in cooked dishes. NCHFP says it loses its crispness when frozen.
• Food stored constantly at 0°F stays safe, says USDA's Food Safety and Inspection Service (FSIS). Freezer times are about quality, and NCHFP puts fruits and vegetables at about 8 to 12 months.

Can You Freeze Chopped Onion, Carrot and Celery Raw?

Of the three, only the onion: NCHFP says diced onions need no blanching before freezing. Diced carrots need a 2-minute water blanch, and celery cut into 1-inch lengths needs 3 minutes. Bell peppers are the easy extra: NCHFP lets you freeze them raw, with no headspace, for raw or cooked use.

Headspace is the gap you leave at the top of a bag or container. Allow enough of it so food can expand without breaking the package seal. Here is what the NCHFP freezing directions give for each vegetable:

Every row comes from NCHFP. Its celery directions call for 1-inch lengths and give no time for finely diced celery. Cut celery to that size for freezing rather than guessing at a shorter blanch.

Why Carrots and Celery Need Blanching (and Onions Don't)

Blanching stops enzyme actions that can cause loss of flavor, color and texture, and NCHFP calls it a must for almost all vegetables headed for the freezer. The cold alone won't do that job. According to FSIS, freezing only slows the enzyme activity in foods; it does not halt it.

FSIS adds that most vegetables that freeze well are low in acid and need brief, partial cooking to prevent deterioration. That short cook is the blanch. NCHFP doesn't explain why diced onions skip the step; its directions simply say no blanching is required.

Watch the clock once you start. The NCHFP blanching guide warns that underblanching stimulates the activity of enzymes and is worse than no blanching. Overblanching costs flavor, color, vitamins and minerals.

How to Blanch and Cool Carrots and Celery

Boil a large pot of water and blanch each vegetable on its own: carrots for 2 minutes, celery for 3. Then chill them in cold water for about as long as they cooked. NCHFP's method uses one gallon of water per pound of prepared vegetables and starts the timer once the water returns to a boil.

Size first: NCHFP's directions call for about 1/4-inch pieces of onion and 1/4-inch cubes or thin slices of carrot, and its celery time is for 1-inch lengths, so leave the celery to a knife. A chopper helps you dice onions and carrots into even pieces, since its grid locks each piece into a fixed size before the blade cuts through. Check one piece against NCHFP's size before you dice the whole batch.

1. Prep and measure. Wash and peel the carrots, and wash and trim the celery. Plan on one gallon of water per pound of prepared vegetables.
2. Boil, then lower. Bring the water to a vigorous boil, lower the vegetables in a blanching basket or wire basket, and cover the pot. The water should return to boiling within 1 minute. If it doesn't, you're using too much vegetable for the amount of water.
3. Time it. Start counting as soon as the water returns to a boil: 2 minutes for diced or sliced carrots, 3 minutes for celery. Because the times differ, blanch each vegetable in its own batch.
4. Cool fast. Plunge the basket straight into a large quantity of cold water, 60°F or below. Change the water often, or use cold running water or ice water (about one pound of ice per pound of vegetables). Cooling should take the same amount of time as blanching.

5. Drain well. Extra moisture can cause a loss of quality once vegetables are frozen, so let them drain thoroughly before packing.

Stick with the stovetop. NCHFP calls boiling water the most satisfactory way to blanch at home, and it cautions that microwave blanching may not be effective because some enzymes may not be inactivated.

How to Pack a Freezer Veggie Base

Pack each vegetable once it is cooled and drained, in bags or containers made for freezing. Leave 1/2-inch headspace for onions and carrots and none for celery. Label every package, then spread the new packages in one layer in the freezer until they are frozen solid, as FSIS advises.

Keep the batch moving while you work. The CDC says to refrigerate cut fruit and some vegetables within 2 hours, or within 1 hour if the temperature is above 90°F.

• Tray-freeze onions if you like: NCHFP's onion directions offer a second method. Freeze the separated pieces on a clean tray, then package them and remove as much air as possible.
• Pick freezer-grade packaging: NCHFP says it must be moisture-vapor resistant, durable and leak proof, and easy to seal. Bags and containers made especially for food freezing give the best moisture-vapor resistance.
• Label it: include the product name, any added ingredients, the packaging date, the amount, and the form of food, such as diced or 1-inch pieces.
• Give it room: FSIS says never to stack packages that are still freezing, and NCHFP says not to overload the freezer with unfrozen food. Stack them once they are frozen solid.

Keep the three vegetables in separate bags. NCHFP gives each one its own cut and headspace, and it has no directions for freezing them mixed. On cooking night, take a handful from each bag.

Keeping some chopped vegetables in the fridge instead? Here is how long chopped vegetables last in the fridge.

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How Long Does a Frozen Veggie Base Last?

Food stored constantly at 0°F stays safe, and FSIS says only the quality suffers with long freezer storage. For quality, NCHFP gives fruits and vegetables about 8 to 12 months at 0°F and says to use the shorter time for best results. Diced raw onions are best used within a few months.

Check that your freezer holds that temperature. The FDA recommends 0°F for the freezer and 40°F or below for the fridge, and it calls appliance thermometers the best way to know.

Use older bags first: NCHFP's rule is "first in, first out." If you freeze a finished soup made with the base, NCHFP's notes on seasonings apply: onion changes flavor during freezing and celery seasonings become stronger, so season lightly before freezing and add more when reheating or serving.

The base belongs in cooked food, especially since frozen celery suits cooked dishes only. Add it to soups, sauces and stews, or use it in these cook-once freezer meals. If you'd rather freeze the finished soup, our guide to freezing cooked soup and leftovers covers it, and FSIS says to reheat leftovers to 165°F and bring soups to a rolling boil.

Signs your frozen veggie base is past its best:

• Freezer burn: grayish-brown leathery spots caused by air touching the food. FSIS says it doesn't make food unsafe, only dry in spots, and you can cut those parts away.
• Dull color: FSIS says dulled color in frozen vegetables usually comes from excess drying due to poor packaging or very long storage.
• Rancid or off odor: some foods develop one when frozen too long, and FSIS says to discard them.
• Past its storage window: NCHFP's general guide for frozen fruits and vegetables is about 8 to 12 months at 0°F, and a few months for raw diced onions. After that, NCHFP says the food should still be safe, just lower in quality.
• Thawed and left out: don't refreeze anything left outside the fridge longer than 2 hours, or 1 hour above 90°F, per FSIS.

Frequently Asked Questions

Can you freeze raw carrots without blanching?

Not by NCHFP's directions. NCHFP's carrot directions call for a water blanch: 2 minutes for diced or sliced carrots. Its blanching guide calls blanching a must for almost all vegetables to be frozen, because it stops enzyme actions that cause loss of flavor, color and texture. Time it carefully, since NCHFP says underblanching is worse than no blanching.

Do you have to blanch onions before freezing?

No. NCHFP says diced onions need no blanching. Dice them into about 1/4-inch pieces and pack them dry with 1/2-inch headspace, or freeze the pieces on a clean tray first.

Can you freeze celery for salads?

No. NCHFP says celery loses its crispness when frozen and the frozen product is suitable only for cooked dishes. Its list of foods that don't freeze well includes celery used as raw salad, which turns limp and water-logged.

How long can you keep frozen chopped onions?

NCHFP says diced onions frozen raw are best used within a few months. Kept constantly at 0°F, they stay safe longer, since FSIS says only quality suffers with lengthy freezer storage.

How should you thaw a frozen veggie base?

FSIS lists three safe ways to thaw food: in the refrigerator, in cold water, or in the microwave. If you use cold water or the microwave, cook the food right after it thaws, and never thaw it on the kitchen counter. Once thawed, handle it as you would any perishable food.

What's the best way to freeze bell peppers?

For raw or cooked use, NCHFP says to package the peppers raw with no headspace. For cooking, you can instead blanch strips or rings for 2 minutes, or halves for 3, and leave 1/2-inch headspace.