Proper Handling

• Handling the onion properly with an eye toward food safety when you slice it helps ensure it stores well and safely for as long as possible. Wash your hands thoroughly before cutting into the onion, and use a clean knife and cutting board to avoid cross-contamination. Store leftover cut onions promptly so bacteria doesn't have a chance to grow on the cut surface and cause spoilage. Cut onions that have been setting out at room temperature for a long time, such as at a picnic or barbecue, are more likely to spoil.

Packaging Tips

• Although whole onions store best in a ventilated bags at room temperature, cut onions require storage in a sealed, airtight container. You can package them in a plastic storage container or zip-top plastic bags. If you use bags, press the excess air out of the bag before sealing it. Label the bag with the date you sliced the onions so you know when to use them to avoid spoilage.

Short-Term Storage

• Cut onions store well in a 40 degree Fahrenheit or cooler refrigerator if you use them within seven days. You don't have to use all the cut onions at once; just make sure to use clean utensils only when dipping into the onions and seal the container completely after each use. Dispose of the onions promptly and sanitize the storage container if the onions develop an off odor, color or show visible signs of bacteria growth.

Freezer Storage

• The freezer provides a suitable storage solution if you need to keep cut and diced onions for more than a week. Other items in the freezer can absorb the odor from onions, but double-bagging them helps prevent this issue. Package the onions in a sealed bag, pressing out the excess air, then seal them in a second bag. Freeze the bags flat in a 0 F freezer. You can store frozen onions for three to six months. They are soft upon defrosting, so frozen onions are best used in cooked dishes.