How to Cut Onions with Fewer Tears
Your eyes sting when cutting onions because, when onion cells are sliced, enzymes react with sulfur compounds and produce a gas called syn-propanethial S-oxide. When this gas meets the moisture in the tear film, it forms a weak sulfuric acid, making your eyes sting and water. In other words, if less of this gas reaches your eyes, you will tear up less.
| Section | Key summary |
|---|---|
| Introduction | In other words, if less of this gas reaches your eyes, you will tear up less |
| 4 key ways to reduce tears | When it is cold, the irritating gas volatilizes more slowly |
| Easier options / variations | Short key point |
4 key ways to reduce tears
- Refrigerate or freeze: Put the onion in the refrigerator 30 minutes before cutting, or in the freezer for 10 minutes if you are in a hurry. When it is cold, the irritating gas volatilizes more slowly.
- Use a sharp knife: A dull knife crushes the cells and releases more gas. Cutting cleanly with a sharpened blade greatly reduces irritation.
- Ventilation and airflow: Turn on the kitchen hood or run a fan on low from the side to move the gas away from your face.
- Leave the root end for last: The irritating compounds are most concentrated near the root. Hold the onion by leaving the root intact, and do not start cutting from the root; handle it at the end.
Using water is also effective. Because the irritating gas dissolves easily in water, lightly wetting the knife blade or soaking a peeled onion in cold water for 5 minutes before cutting can reduce the pungency. However, soaking it too long will wash out sweetness and texture, so do not exceed 5 minutes.
Below is a quick prep flow for slicing onions thinly while minimizing tears. For one onion, it takes about 2 minutes.
Easier options / variations
- Breathing through your mouth and holding your breath through your nose reduces mucous membrane irritation, so you tear up less.
- Some people say that keeping a candle or gas stove flame lit nearby burns off some of the gas and weakens the irritation.
- When chopping a large amount, using a food processor keeps the gas trapped inside the container, so it barely reaches your eyes.
- If you put a peeled onion in a plastic bag and store it in the refrigerator, it will also sting less the next time you cut it.
Store leftover cut onion in an airtight container in the refrigerator so the cut surface does not dry out, and use it within 3 to 4 days. To prevent the onion smell from spreading through the refrigerator, wrap the cut surface with a paper towel before storing it.