How No-Stick Knives Work

How many times have you gone to cut open something large like a watermelon or a butternut squash, only to have your knife get stuck halfway through trying to cut it in half? Then, to add injury to insult, once your knife is wedged in, it’s a lot harder to un-wedge, even by pulling it out or up. This is when a lot of home cooks will brace a hand on the side of whatever they are cutting, to try to force the knife out, and end up cutting themselves in the process. If you’ve had a food preparation experience or two like this, it’s time to get some help. It’s not the butternut squash’s fault the knife keeps getting stuck—it’s your knife!

Why Knives Stick

Foods like squash (of all varieties), watermelon, even potatoes or yams are often the worst offenders for suctioning onto your knife and refusing to let go. Most meats and vegetables aren’t that bad because they’re small enough that they can’t offer a whole lot in the way of resistance. But those watermelons, honeydews, and butternut squash are all large and dense enough that it’s a different story. What’s going on here is a combination of dense material and surface tension. When you chop a potato or onion, you’ve probably noticed that several cubes or slices will stick to your knife blade as you cut it apart. This is because of the surface tension inherent to the structure of liquids, especially water.

Think about spilling a couple drops of coffee on your breakfast plate. Instead of spreading thin, the liquid beads up and holds together as much as it can. The elasticity of liquids comes from the attraction those liquid molecules have to each other, compelling them to try to hold together, while being acted upon by gravity. Since most vegetables are high in water content—some are up to 90 percent water—the surface tension of the water in a vegetable will try to cling to itself, even as you’re dividing it with your knife. When enough moisture collects on your knife, like clings to like and the water in the bits of onion (or whatever you’re chopping) will cling to the water on your knife and cause some pieces to hang on to the knife. When you’re cutting into a watermelon, the same thing is happening; it’s just harder to notice. The liquid in whatever you’re cutting into is trying to cling to the liquid on the knife. Add in the pressure from gravity and the force from both sides of the watermelon or squash pressing in on the knife, and it’s pretty easy for that slick knife to be suctioned by all that force and get stuck.

How to Avoid It

The primary step to avoid getting your knife stuck inside foods is to ensure you’re using a well-honed knife. As we’ve discussed before, a sharp blade edge means you have to exert less force as you cut. However, if you’re using a sharp knife and it still gets stuck, it’s probably time to upgrade your knife. First, you’ll want a larger knife as the longer blade will better be able to fight against the pressure being exerted by the ingredient. Second, for large foods and those with tough exteriors especially, a serrated-edge knife will be easier to push and pull out. Finally, look for a no-stick knife.

A no-stick knife is designed to fight back against the suction and pressure that comes from those heartier ingredients. These are knives that have notches, ridges, or openings intended to relieve the pressure so the knife won’t get stuck. At Easy Cut, we’ve designed our knife blades to be sturdy, so they will hold their edge through a great deal of use—even heavy, dense foods like squash—but we also designed them to cut easily. The double scallop edge helps you cut easily and straight every time, and the specially designed open spaces in the blade reduce where the water can collect, making ours a zero-friction blade. That’s right, our serrated-edge knife blade is designed to avoid getting stuck, even when cutting the toughest ingredients.

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