How to Store a Cut Onion

Sometimes you only need to cook with a portion of an onion, and you may not be sure what to do with the rest. Fortunately, you can store cut onions, but they need to be stored differently than whole ones. Without their exterior layers intact, cut onions are susceptible to bacteria and mold. To reuse a cut onion, you'll need to prepare it correctly, choose an appropriate container, and store it at the right temperature. With a little preparation, you can enjoy the rest of your onion when the time is right.

Method 1

Method 1 of 2:

Refrigerating a Cut Onion

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1
Keep your onion clean when preparing it for storage. Minimize exposure to harmful bacterial by preventing cross-contamination with uncooked meat and dairy products. Use separate cutting boards for meat and produce. Always wash your hands after handling uncooked meat and ensure that your knife is clean.
- If you have space, consider setting up dedicated areas for produce and meat preparation, so you don’t spread germs while cooking.
- Avoiding cross-contamination is especially important when preparing food for storage because storing food allows bacteria time to grow.
If you have half of an onion remaining or a few large wedges, then wrap them tightly in plastic wrap. Plastic wrap will insulate the onion from the outside air while helping it retain moisture.^{[1]XResearch source}
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If you have smaller pieces of onion left over, use a resealable bag to store them. Never use cloth storage bags, as these are intended for whole produce and will not protect a cut onion from exposure to air.^{[2]XResearch source}
4
Consider reusable containers if you have them. You can find airtight plastic containers for food storage at any big box store. These containers work great for refrigerating cut onions.
- There are also new, silicone products designed to stretch over and cover the exposed side of cut produce. Exercise caution when using these with onions. These products will not fully encase an onion, which can cause your refrigerator to smell.
5
Store onions in your refrigerator at or below 40 °F (4 °C). Cut onions should always be stored in your refrigerator—not at room temperature. Keeping them at a low temperature inhibits the growth of bacteria and allows you to safely reuse them later.^{[3]XResearch source}
- Ignore any storage recommendations that suggest that cut onions can be stored at room temperature. Some common tips include storing onions in a bowl of water on a countertop. This approach only promotes bacteria growth.^{[4]XResearch source}
6
Use or discard cut onions after 7-10 days. Try to reuse refrigerated onions as soon as possible. However, never use them if stored for over 10 days.^{[5]XResearch source}
- Store all cut onions for the same period of time regardless of variety. Even though you may find different storage recommendations for different onion varieties—such as yellow, white, red, pearl, or Vidalia—these recommendations are relevant only for whole onions, not for cut ones.
Throw away onions that appear cloudy, mushy, slimy, or moldy. Smell the onions to make sure there is no unusual odor, and if they give off an strong or unusual odor, dispose of them.^{[6]XResearch source}
Never serve previously stored onions raw. You’ll need to cook them first because the heat will kill off any bacteria that may have grown during storage.^{[7]XResearch source}

Method 2

Method 2 of 2:

Freezing a Cut Onion for Extended Storage

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1
Chop the onion into small pieces. Large pieces of onion—like an onion half or wedges—do not freeze well. To freeze effectively, you’ll need to chop your remaining onion into small pieces, preferably¹⁄₄ inch (6.4 mm) cubes.^{[8]XResearch source}
- Smaller onions freeze more evenly whereas larger sections often become freezer burned.
2
Put the chopped onion into a freezer-safe container. You can use freezer-safe resealable bags. Alternatively, use a freezer-safe container made of either glass or plastic. Regardless of the type of container you select, make sure that the onion is spread out as thinly as possible. The thinner you spread the onion, the more evenly it will defrost when you’re ready to use it.^{[9]XResearch source}
- You don't have to blanch your onions beforehand if they're chopped.^{[10]XResearch source}
3
Write the date you cut the onion on the container. Either write the date legibly on the container itself, or write it on a label or piece of paper. Stick the date to the container.^{[11]XResearch source}
- It’s easy to forget when you put something in the freezer. Having the date written on your onion container will ensure that you don’t lose track of when you stored it.
Even though your onion is frozen, it won’t last forever. Check the date before using it to make sure it has not been stored for more than 8 months.^{[12]XResearch source}
Frozen onion becomes soft and sometimes quite mushy when cooked. Use previously frozen onion for stews, soups, casseroles and other dishes where the onion’s soft texture will be less noticeable.^{[13]XResearch source}
Don't worry about trying to defrost your frozen onion before cooking. In fact, defrosting your onion before cooking will only lead to a mushier texture. If you only need to use a small portion of your frozen onion, and the pieces are frozen together, run the container under warm water until you can separate out the amount that you need.^{[14]XResearch source}

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Question
How do I store Vidalia onions uncut, with the skin on?
Community Answer
I would just put them in a dry, dark place. Keep them in the packaging they came in, or store them in a plastic container.
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How can I store several kilos of cut onion?
Community Answer
If you have the room in your freezer, then that´s an effective method. If you can, freeze the onion spread out on a sheet and then place it in containers, that way you can pick out the exact amount you need later.
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Can I chop onions in advance?
Community Answer
Yes! I always chop one or two onions into small pieces and store them in a Ziploc bag; they'll keep very well for a week or so. You can store them in plastic containers if you prefer, but it can be a challenge to get the onion smell out of the container.
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Tips

Treat all chopped onions the same regardless of variety.
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Make sure to select onions that are in good condition, so they will last longer when stored. Avoid onions with spots or soft spots.
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Warnings

Don’t confuse instructions for cut and uncut onions.
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Follow instructions on the package if you purchased precut onion. These may have been prepared a long time ago and may not last as long as a recently cut onion.
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