
Tools used for grinding and mixing food, making ingredients into a smooth paste
What are mortar and pestle?
A mortar (すり鉢 in Japanese) is a tool for grinding and mixing ingredients. It is used in combination with a wooden stick called a pestle (すりこ木 in Japanese). It is used to grind roasted sesame seeds, or to make a dressing for salads by adding seasonings to ground tofu. It is also used to grate Japanese mountain yams directly in the mortar to make tororo sticky yam paste. As of recently, there have been mortars with spouts and small sizes that are also available for use.

How to use
Hold the center of the pestle with your dominant hand and place the other hand on the top of the pestle. Move the tip of the pestle in a circular motion inside the mortar. It is difficult to apply force when the mortar moves, so placing a damp cloth or towel that has been wrung out tightly under the mortar will make it less likely to slip.
Substitute for mortar and pestle: when you don’t have it
If you have a small amount of sesame seeds, you can grind them by putting them in a plastic bag and tapping them lightly from above with a wooden mallet. Substitutes vary depending on the ingredient; for example, tofu can be placed in a bowl and crushed with a whisk, while yam or mountain yam can be grated with a grater.
Trivia
A mortar can be used in a variety of ways. You can use it to grind tea or black tea leaves to add to cakes or cookies, mash nuts, avocados or boiled potatoes to add to salads, and it's also useful for making baby food.
Caution
If dirt is left in the grooves of a mortar, it can cause molding. When you're done using it, use a scrubbing brush to remove dirt along the grooves and dry thoroughly before storing it away.