Photo: Ilona Kozhevnikova (Shutterstock)
I don’t use my standard blender all that much, unless I need to puree a soup. I use my immersion blender on a weekly basis, mostly to make dressings, sauces, mayo, and other emulsions; occasionally I’ll also use it to make a smoothie or a quick milkshake. It has never occurred to me to sharpen the blades of either blender, because blender blades are meant to crush, crumble, and mash, rather than slice and dice. Still, someone must be looking for a way to sharpen these little things, because there is a viral hack for it going around. Unfortunately, the hack is bad.
Type “how to sharpen blender blades” into your search engine, and you will be rewarded with two types of articles: Those suggesting you hone and sharpen them just as you would a knife, and those telling you to toss a bunch of eggshells and water into your blender. Don’t do the latter. It doesn’t make any sense.
What is sharpening anyway?
As we’ve discussed previously, honing and sharpening are two different things. If you were to look at a blade under a microscope, you would see a bunch of tiny teeth, even on the smoothest, thinnest blade. Those teeth are what do the cutting. When they get out of alignment, they cut less cleanly, and require more pressure to cut through whatever food you happen to be slicing into. Honing realigns the teeth; sharpening creates new teeth by shaving the old metal away. Eggshells are capable of doing neither.
Why won’t eggshells sharpen my blender blades?
This is one case where the wheel truly does not need to be reinvented, or even lightly modified. According to this 1979 Washington Post article (and basic common sense), you cannot sharpen a blade with a material that is softer than the blade itself:
The metal can be straightened out by the use of a sharpening steel. However, it is essential to use a sharpener that is harder than the blade of the knife, or you end up sharpening the sharpening steel. Sharpening takes place when the harder material wears away a small part of the softer substance.
Ah well, nevertheless.
I need not measure the tensile strength of eggshells and blender blades to determine which is harder. I cannot crack a blender blade with a quick flick of my wrist, so it stands that I cannot sharpen a blender blade with something that can be cracked in that manner. The only thing you’ll get by tossing a bunch of eggshells into your blender is eggshell paste and, potentially, slightly duller blades.
Another popular “hack” suggests blending aluminum foil. Again, that will not work, because the blade is harder than the foil, but it’s also a matter of direction. When you hone or sharpen, you are move your blade in one direction with deliberate pressure to either realign the existing teeth or shave off old metal to create new teeth. Eggshells in a blender move in all sorts of chaotic directions, which makes the incapable of realigning anything.
How should I sharpen my blender blades?
I don’t know what you are blending that has dulled your blades so. (Unless you’re the Blendtec guy; then I know exactly what you’re blending, and it is unhinged.) Smoothies and soups do not require the clean slicing provided by a freshly sharpened of honed knife. Still, things wear with use, and if you are an active blender, sure, you might notice your blades aren’t blending as effectively as they used to.
First things first: Check with your blender manufacturer. Some, such as Ninja, will tell you to “never try and sharpen the blades.” If that’s the case, and your blades aren’t doing what you need them to do, I recommend reaching out to the manufacturer and asking for a replacement.
But if you’re into voiding warranties and wish to DIY it, it’s not that hard: You can hone and sharpen blender blades just as you would a tiny knife. Gadget Review can walk you through the process in writing, but this man from Sharpens Best can show you. His video is rambling, but entertaining, and he shows off a few mini sharpeners that make the job even easier. (He starts the sharpening at around 5:40.)
Save your eggshells for compost, or whatever it is gardeners do with them. Don’t put them in your blender, and definitely don’t put them in your garbage disposal—eggshells may not be able to sharpen anything, but they will wreak havoc on your garbage disposal.
Edited on March 1, 2023 at 12:40 p.m. EST to add information about direction of motion and how it relates to honing and sharpening.