How we tested
You've seen them on TV and in kitchen stores: serrated plastic knives that supposedly help prevent your lettuce from turning brown after cutting. But do they work better than tearing or using an ordinary kitchen knife? We chopped a head of romaine lettuce and a head of iceberg lettuce using three different knives: one with a stainless steel blade, one with a super-thin high-carbon steel blade, and the Zyliss Fresh Cut Salad Knife. We also tore the leaves by hand. After chopping and tearing, we refrigerated the lettuces in plastic zipper-lock bags and waited fo them to brown. Though all lettuce began showing some browning on the ribs after 10 days, none showed any signs of browning on the cut or torn surfaces. After 12 days, the heads cut with metal knives showed faint signs of browning on these surfaces, and the lettuce cut with the plastic knife followed a day later. The torn lettuce was last to brown on its ruptured edges, starting to turn at 2 weeks.
Our verdict? The plastic lettuce knife might stave off browning slightly longer than metal knives, but it's not worth the money or the extra drawer space. To prolong the life of lettuce by a day or two, stick to tearing by hand. Tearing allows leaves to break along their natural fault lines, rupturing fewer cells and reducing premature browning.