No need to round up a box of tissues before setting out to make homemade French onion soup.
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We can’t be the only ones who look like they just finished watching This is Us or The Notebook for the 37th time after cutting onions or shallots. It’s clear that we’re not, as the topic has sparked countless newspaper comics. It’s also the inspiration behind dozens of silly hacks to prevent the reaction while chopping (ranging from lighting a match to chewing on bread to putting a spoon in your mouth). Spoiler: Each of those is about as effective as trying to buy a Taylor Swift concert ticket by walking up to the ticket counter the day of the show.
The tear-inducing qualities of onions and their allium siblings are so ubiquitous that “how to cut onions without crying” pulls up 2.3 million search results on Google. The science behind this reaction offers hints about how to tackle the task tear-free next time. So before you set out to make your next batch of French Onion Baked Brie, Caramelized Five-Onion Dip, Free-Form Onion Tart, or French Onion Soup, read on for the secrets.
Why do onions make you cry?
This reaction is actually for a very savvy scientific reason. Onions make us — and other living beings — have a strong reaction when we damage their cell walls as a self-defense mechanism.
Onions grow underground, where many other critters live and search for food. When an onion is sliced or broken open, sulfoxides and onion enzymes are emitted in the form of sulfenic acid, according to ophthalmology experts at Texas A&M College of Medicine. As that acid and the onion enzymes interact, they create syn-propanethial-S-oxide gas. That gas is the molecule that wafts up to your eyes, reacts with the water naturally covering your eyes, and generates sulphuric acid and other irritating substances that can induce tears. (The same happens to animals that try to eat onions underground as they’re growing.) Our eyes are very sensitive since they’re involved with such an important task: vision.
White, yellow, and red onions in particular have high concentrations of the onion enzyme necessary to max out this reaction, while sweet onions, green onions, shallots, and scallions have lower levels. Still, many alliums can produce somewhat of a “lachrymatory process,” aka, a sensation that makes you tear up at least a little.
How to cut onions without crying
As we mentioned, nearly all the tear-free onion-cutting hacks will make you look silly and eat up your time rather than deliver dry-eyed results. However, since the enzymes involved tend to work best under certain pH, temperatures, and environmental conditions, there are a few strategies that tend to reduce the risk or severity of tears. Try these tips the next time you’re whipping up your favorite onion recipe.
Start with a sharp knife. Using a sharp knife while cutting onions will drastically trim down the amount of cells you’ll bruise. As a result, fewer enzymes will be released, thus, fewer tears.
Freeze for 30 minutes. Pop the alliums in the freezer for half an hour before you plan to slice or chop. This will stall the enzymatic chemical reactions.
Protect your eyes. If you wear contacts, you have natural defenses of your own. These work terrifically well to reduce exposure. Those goofy-looking onion goggles (or ski goggles) also work if you don’t need corrective lenses.
Add acid. A splash of citrus juice or vinegar alters the pH enough to hamper the enzyme’s ability to function as usual.
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