I was talked into buying a plastic knife designed to cut lettuce. I was told that cutting lettuce with a metal knife makes it go bad faster.
Is it true? Does cutting lettuce with a metal knife make it go brown faster?
If so, then why? How many molecules of metal will come off a stainless steel blade to be left on the lettuce that it could make any difference?
What other foods, or anything else, might depend on the makeup of the knife used to cut it?
I always thought that cutting leaves like lettuce causes browning because it crushes the cut edge (tearing the leaves doesn’t).
If that’s right, then a plastic knife would be worse, because it’s bound to be wider than a metal one.
A wag here - the plastic knife is more likely to rip the lettuce rather then cut it. ripping causes the lettuce to come appart at weak points that don’t cause browning
You may get browning if you use a crummy old knife that bleeds metal ions every time you cut something with it. Iron, copper, manganese, etc. will all speed up oxidation reactions (browning) by making oxygen more reactive. I doubt that this is much of a problem with modern steels blades.
My understanding is that a sharp knife actually slices through the cell wall, leading to faster browning.
Tearing (or cutting with a dull plastic knife) will not destroy the cell walls, but separates the cells from one another, which leaves the leaves’ edges protected so they don’t brown.
So, I am to understand that the difference has nothing to do with the material the knife is made of. If I were to cut my lettuce with dull, clean, metal knife, it would rip rather than cut the cells and it wouldn’t brown, same as the plastic knife?
I was about to post this same question, but a search found this old thread.
I had never heard of a lettuce knife until a week or so ago when I saw one in a grocery store and commented about it to my wife. She informed me that the reason you’d want a plastic knife is that the metal causes the lettuce to brown. I thought about it for a bit, and I can’t see how enough metal atoms in my nice chef’s knife could react with the lettuce to cause anything significant. If it did, I’d expect lettuce to cause severe knife corrosion over time.
So I filed it away in my brain under “Doubtful, needs more research.” But that research didn’t turn up anything but a bunch of sites selling plastic knives which mentioned that metal knives cause the lettuce to turn brown.
So here I am - after eight years, has the state of metal-lettuce chemistry knowledge advanced?
No idea, but you can do an experiment. Take a head of lettuce. Cut off one edge of it with a metal knife. Find some sort of plastic that is thin and rigid, use that as an imprompru knife and cut another portion off, then tear manually another portion off. Set them all aside, packaged identically and examine them 24 hours later.
It’s a food myth. Plastic knives are good for if you have to slice some food in a non-stick pan, though.