Sharp knives are intuitively thought of as more dangerous – and I understand why. Sharpness leads to elevated ease of cutting, which many people process as “I’ll cut myself deeper, more easily”. While not untrue, the goal of proper knife technique is to keep your hands out of the way of the blade, so you shouldn’t need to factor in how badly a sharp knife might injure you. In fact, it’s exactly the sharpness that makes a sharp knife a safe knife. The sharper the knife, the less effort you need to pass it through something, so you can be more gentile with it.
Try using a dull knife to cut a lemon in half. It’s very likely that the knife won’t penetrate the rind, and instead, the harder you try, it will glance off to one side, likely (and forcefully) running into — and cutting one of your fingers holding the fruit in place. That’s when you learn the hard way, that human skin isn’t as tough as that of a lemon – and ironically, you’ve given yourself a cut worse than you would have with a sharp knife.
Like anyone who has cooked as long as I have, I’ve cut myself a bunch of times with a bunch of stuff. The reliable constant is that the sharper the knife, the less it hurts and the faster it heals. The most painful cuts I’ve ever had have come from jagged wine foil, and the cutter on a spool of plastic wrap. Yet, I’ve twice cut myself with brand new, sharp as they’ll ever be, knives (both times down to the bone!), and I literally didn’t feel anything either time. Furthermore, in those instances, I pinched the cut closed until a bandage could be applied, and the cuts were healed in days, not weeks (albeit with minor, semi-permanent nerve damage, and noticeable scar tissue).
To illustrate the importance of a sharp knife, regarding the food you’re cutting, try thinking about the physics of slicing on a microscopic level with me: Every fruit or vegetable is made up of tiny little pockets of… whatever; let’s just call it “juice”. A sharp knife will disrupt as few of those pockets as possible, the juice released will be minimal, and the appearance of the severed area will be as clean and bright as the whole piece. On the other hand, a dull knife won’t “slice” those pockets, so much as it will crush them, causing many more to pop and release juice, than would the slice of the sharp knife. This will result in more juice being released, and the end product looking dull and sloppy (a chef would call this “bruising”).
Cutting some things like alliums or peppers with a dull knife, actually makes a different sound; more of a crunching (imagine a snare drum with loose strings), whereas a sharp knife’s cut would be more akin to a clean tapping (tighten those strings up!). I once worked for a chef who loved chives, and they were required for the mise en place of every station in the kitchen, sliced as thinly as possible. Furthermore, at a fine dining restaurant such as this one, thin-sliced chives needed to be done fresh daily, as the delicate flavor and vibrant color would change drastically (and negatively) in 24 hours. A (almost always) new-ish cook would eventually commit the heinous offense of bruising his/her chives. Chef would get furious when he heard the crunching sound, and would yell at them, often from across the kitchen: “What are you doing? You’re hurting them! Listen — they’re screaming at you, and you’re bruising them! look!” This was almost always because the cook’s knife wasn’t as sharp as it needed to be for that task.
Going back to the sharp knives bursting microscopic juice pockets, let’s return to the most common allium: onions. Everyone knows cutting onions makes you cry, but few people actually know why. It turns out that the “pockets” of onions actually contain (among other things) sulfuric acid gas. When the pockets are cut open, the gas is released into the air, and when your eyes come in contact with this gas, they react with tears to rinse it away. Try slicing half an onion with the sharpest knife you have, then try slicing the other half with a bread knife. Your eyes won’t lie to you (now that’s what I call an eye test!). This is why the only trick I’ve heard to actually prevent this (other than wearing swimming goggles) is to cut onions with as sharp of a knife as you can.
When it comes to sharpening your knife, that will have to be a different post, but a few passes on a honing rod before each use should be sufficient behavior to maintain a sharpened edge. If you know you need a given knife sharpened (but are uncomfortable with doing it yourself), check online for local places around you that offer sharpening services, find the one with the best customer reviews and take your knife in.
As cooking just about anything starts with knife work, it’s important to have an intimate and educated relationship with your most important tool. Cleanly-cut ingredients lead to cleaner, happier food, and I don’t care how good of a cook you are, or how keen you are with a knife, if that knife isn’t sharp, nothing’s getting done well.