How to sharpen your knives for sushi

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Knives are sharpened with so called whetstones (also called sharpening stones or water stones). These stones are available in various grit sizes, which are based on European (F) or Japanese (J) standards. In general, the higher the number, the finer the grit, the finer the result. Many whetstones are double-sided: a low grit side for re-sharpening, and a high grit side for polishing. Keep in mind that it takes longer to sharpen a knife with a finer grit, because it removes less material.

Fun fact: whetstones are not named after the water used to lubricate the stones. The word ‘whet’ means to sharpen a blade. The process of using a sharpening stone is called ‘stoning’.

Instructions

Step 1: preparing the whetstones

Start by submerging the whetstone in water for 10 to 15 minutes. When no more little air bubbles appear, the stone has absorbed the optimum amount of water. Now you need to flatten the stones. This is important: if your whetstone is not completely flat, it can ruin your expensive sushi knife!

Flattening whetstones is done with a flattening stone or lapping plate (a coarse, flat stone used to flatten other stones). Draw a grid or a number of mark lines with a pencil on the whetstone. Start rubbing the whetstone by moving it against the flattening stone back and forth. Continue rubbing until the pencil marks are gone. This indicates that the whetstone is flat and ready for use.

Step 2: sharpening the knife

Place the whetstone on a non-slippery surface or put it in a whetstone holder. First use the low grit side of the stone. Move the blade back and forth across the entire stone with light pressure at an angle of 10 to 15˚ (roughly the height of the little finger of an adult).

Start at the tip of the blade. Slightly lift the handle. Pull the blade over the stone through to the middle and down to the base of the blade. Repeat this several times. Turn the knife around and work on the other side of the blade. Don’t press the knife hard against the stone, but let it glide over the stone.

Do each side twice for 5 minutes. So the whole process should take 20 minutes. Watch the video on the right to see how it’s done.

Note: some Japanese knives are only sharpened on one side only. If you are sharpening such a knife, do not sharpen the flat side. Rather lay it flat on the stone to remove any curling metal ‘burr’.

Step 3: polishing the knife

Repeat the above process for the same amount of time using the high grit side of the whetstone. This will make your knife really sharp.

Maintain the same angle at every step.
Keep the whetstone wet when sharpening your knife.
Don’t wipe off the grinding residue while sharpening the knife. This residue helps sharpen the knife!
When done, rinse the whetstone and wipe off the grinding residue.
Rinse the sharpened knive in hot water.

Step 4: testing the sharpness

Here are 4 simple methods to test the sharpness of your sushi knife.

Slice a piece of paper. The knife is sharp enough for sushi if you can effortlessly cut the paper into thin strips.
Slice a wet sponge. If you can cut off a piece effortlessly, your knife is sharp enough for sushi.
Slice a tomato horizontally into thin slices. If you can do this without touching the tomato with your hands, your knife is really really sharp.
No paper, sponge or tomato available? Shave off some hair on your arm. Place the knife horizontal on your arm and with a gentle stroke shave off some hair. Note: this method is not recommended. Chef Davy or any of the co-operators of Makesushi.com are not responsible in any way for injuries as a result of testing the sharpness of knives in this way!

Utensils

Whetstone F8000 grit
Whetstone F1000 grit
Flattening stone or lapping plate
Whetstone holder (optionally)
Knife (click here for the knife used in the video)
Pencil
Water

Which whetstone to buy?

I recommend a low grit between F1000 and F3000 for grinding down the metal and sharpening the knife. To finish the sharpening (polishing) I recommend a high grit between F5000 and F10,000.