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Do metal knives make lettuce turn brown? No, and here’s why they don’t

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Quite possibly one of my favorite aspects of writing this column is the mountain of reader feedback it produces.

I have the best readers in the universe, too. Nearly every letter turns into a love fest, which of course charges my batteries, making me love my readers all the more!

Do you recall the letter from Pat, who complained of her lettuce turning rusty? I responded the rust-colored stains on lettuce are harmless evidence of the natural breakdown process and an indication the produce is not exactly fresh. The parts that are turning brown can be cut away, while the rest of the lettuce remains perfectly edible.

Well, that question together with my response brought in a tsunami of input from readers insisting Pat’s problem is that she is cutting her lettuce with a metal knife.

Jenny wrote: “While working in a restaurant, a decade ago, I learned to either cut the lettuce with a plastic knife or tear it. I do not know the science behind why metal causes the lettuce to brown but my lettuce stays fresher looking days longer since I stopped using metal knives.”

While this might sound like a plausible explanation for why lettuce turns brown, I’m sorry to tell Jenny and the dozens of others who wrote about using a plastic knife instead of a metal one to keep lettuce fresher longer: It’s a myth. There is no truth to the rumor.

If you believe your lettuce stays fresher longer when you cut it with a plastic knife, the truth is, it produces the same outcome as using a metal knife. The enemy of lettuce is time plus oxygen, not metal. Exposing the inside of a head of lettuce to oxygen is going to hasten its breakdown, whether you cut it with plastic, metal or a laser beam. It’s going to turn brown.

Personally, I blame Tupperware parties for founding this myth. Back in the 1970s, the company came out with a little plastic knife, or “corer,” that it included with its Lettuce Crisper. The instructions were to cut out the heart of the lettuce head, insert a plastic pointy thing where the heart used to be and then store it in the crisper.

Tupperware dealers were instructed to tell party attendees that cutting lettuce with metal would make it turn brown, and that to combat this horrible waste of money, they needed this plastic coring knife-like gizmo. I believed; I bought it; and so did millions of others. And here we are, all these years later, many still believing this vintage piece of culinary lore. I’m convinced it was nothing more than a brilliant marketing ploy.

There are lots of ways to slow the lettuce dying process so it stays fresher longer: Wait to wash it until you’re ready to use it. Store it in a sealed glass container. Wrap it in a paper towel to wick away moisture. Keep a Bluapple ethylene gas absorber in the produce bin of your refrigerator or the fruit bowl on your counter.

All are excellent tips with provable results. But the mother of all tactics that will keep produce fresh at least long enough to use it up is to vacuum seal it by removing all of the oxygen — the arch enemy of fresh produce.

Mary Hunt, founder of, writes this column for Creators Syndicate. Send tips or address questions to: Everyday Cheapskate, 12340 Seal Beach Blvd., Suite B-416, Seal Beach, CA 90740, or email her at


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