TL;DR
A box grater has four different problems, not one. The coarse shred side rinses clean in seconds, while the fine rasp face clogs with a paste that hot water alone will not move. Clean each side separately, brush in the direction the blades point, and stand the grater upright to dry so water does not sit inside the box.
Why the four sides need four approaches
The whole point of a box grater is that each face cuts differently, so each face fouls differently. Treating it as one object is why people end up scrubbing for five minutes and still finding cheese in it.
The coarse shred side has large, well-spaced teeth and clears easily. The medium side packs a little. The fine rasp face, with its dozens of tiny raised punctures, holds a paste of cheese fat, citrus oil, or garlic that behaves more like glue than like crumbs. The slicing blade -- the one long slot on the fourth side -- is the sharpest part of the tool and the one most likely to cut you during cleaning.
Start with the easy faces so you are not dragging soil around, and save the fine side for a soak. The general approach to cleaning kitchen tools without damaging them applies here in miniature.
How do you clean the fine side of a box grater?
Soak the grater face-down in hot soapy water for ten to fifteen minutes, then push a stiff brush across the rasp face in the direction the raised burrs point. The soak softens the fat paste so bristles can lift it out of each tiny cup instead of smearing it flat. Rinse from the inside of the box outward.
Brush direction and the slicing blade
Every raised tooth on a grater is a small blade with one sharp edge. Brushing into that edge shreds a sponge and can shred skin. Look at the face, note which way the lips point, and run the brush that way.
The slicing slot deserves its own caution. It is a full-length blade, it is usually the sharpest surface in a home kitchen after a chef's knife, and it is easy to forget about while you are focused on the cheese side. Hold the grater by the handle or the frame, never by wrapping a hand around the slicing face, and clean that side by running the brush along the slot rather than across it.
If a shred refuses to move, a wooden skewer or the corner of an old toothbrush handles it. Fingers are the wrong tool.
Soaking rules
Ten to fifteen minutes in hot soapy water is the sweet spot. That is long enough to soften set fat and dried citrus pith, short enough that you are not leaving food-soiled water sitting on metal.
Do not soak overnight. Standing water at a rivet, weld, or handle joint is where rust starts, and food residue in warm water grows bacteria. If a grater is bad enough that fifteen minutes has not helped, do a second short soak rather than one long one.
Graters with wooden handles or wooden bases skip the soak entirely. Wood swells, splits, and pulls away from the metal. Wash those quickly and dry them right away, the same way you would treat how to clean a wooden cutting board.
Drying upright is the whole trick
Stand the grater on its widest opening in a dish rack with the faces exposed to air. Water trapped inside the box, or held in the fold of a tooth, is the reason otherwise good stainless graters develop freckles of surface rust.
Stainless steel resists corrosion because of a thin passive oxide layer, and that layer is weakest at stamped and cut edges -- which is to say, at every tooth on the tool. Source: ASTM International stainless steel guidance. Air drying the edges is more useful than towel drying the flat panels.
Give it ten to fifteen minutes upright before it goes in a drawer.
Dishwasher, bleach, and abrasives
Most all-metal box graters and metal graters with plastic frames are dishwasher safe on the top rack, and the dishwasher does a reasonable job on a grater that was rinsed after use. It does a poor job on dried-on cheese, because that needs mechanical contact.
Load it so the blade faces point away from where hands reach in. Never lay a grater loose in the lower rack.
Skip chlorine bleach on stainless entirely. Chloride ions attack the passive layer and cause pitting, which is permanent. Skip steel wool too -- it leaves iron particles behind that rust on their own and scratch the finish. Baking soda paste on a soft cloth handles staining without either problem.
Odor and flavor carryover
The fine rasp face is where garlic, onion, and citrus oils linger, and they will show up in the next thing you grate. Wash the fine side first with hot water and dish soap while the oils are still soft, since oil sets like a varnish once it dries.
For stubborn carryover, a paste of baking soda scrubbed with a brush and rinsed hot usually resets it. Skip vinegar soaks on graters with aluminum components, which pit and discolor in acid.
The same oil problem shows up on any fine-toothed tool, which is why how to clean a rasp zester covers nearly identical ground. Our house cleaning services page has the wider kitchen context if tool care is only part of what you are tackling.
FAQ
How do you clean the fine side of a box grater?
Soak it face-down in hot soapy water for ten to fifteen minutes, then brush the rasp face in the direction the raised burrs point using a stiff dish brush. Push from the inside of the box outward so plugs of food pop out rather than compacting further into the holes.
Can a box grater go in the dishwasher?
Most all-metal and metal-and-plastic box graters are dishwasher safe on the top rack. Position blade faces away from where hands reach in, and never lay one loose in the bottom rack. Graters with wooden handles or bases must be hand washed, since dishwasher heat and moisture damage wood.
Which way should you brush a grater?
Brush in the direction the raised teeth point, never against them. Each tooth has a single sharp edge, and moving into that edge catches and tears sponges, cloths, and skin. A long-handled dish brush keeps your hand well clear of every cutting surface on the tool.
Why does my box grater rust?
Water sitting in the folds of the teeth or at a rivet seam breaks down the thin passive layer that protects stainless steel, especially at stamped edges. Standing the grater upright to air dry for ten to fifteen minutes after washing prevents most of it. Chlorine bleach makes it worse, not better.
How do you get garlic or onion smell out of a grater?
Wash the fine face with hot water and dish soap immediately after use, while the oils are still soft. For set-in odor, scrub a baking soda and water paste over the face with a brush and rinse hot. Avoid vinegar soaks on graters with aluminum parts, which pit in acid.
Small tools add up, and they are usually the last thing anyone gets to. If you would rather hand off the kitchen entirely, every home is different, so the real number depends on size, condition, and what you want covered. Get a quote and we will walk you through it.