How to Clean a Clay Mortar and Pestle

To clean a clay mortar and pestle, rinse both under warm running water right after use and scrub away food residue with a soft brush or sponge. Use little or no soap, and never put either piece in the dishwasher or leave it soaking. Then let them air-dry completely in a ventilated spot before storing. Unglazed clay and raw wood are both porous. They absorb water, oils, smells and soap, so quick, gentle cleaning keeps them hygienic and keeps them from cracking or tasting stale.

What Is a Thai Clay Mortar and Pestle?

A Thai clay mortar, called krok din in Thai, is a deep, unglazed terracotta bowl used mainly for pounding salads such as som tam, green papaya salad. It is usually paired with a long wooden pestle.

How to recognize it

• Color: warm orange, rust-red or earthy brown. With use, the inside often darkens and picks up faint stains from chilies and tamarind.
• Shape: tall and deep, with a narrow base that flares toward the rim. This shape keeps juices and shreds of papaya inside while you pound and toss.
• Texture: matte, slightly rough and dry to the touch. It is clearly porous, unlike the cold, heavy, polished feel of stone.
• The pestle: a long, light-colored wooden club, smooth from handling. It is lighter than a stone pestle because it is meant to bruise ingredients, not grind them to paste.

What it contributes to a dish

In som tam, the cook lightly crushes garlic and bird's eye chilies, then adds fish sauce, lime juice, palm sugar, tomatoes, long beans and shredded green papaya. The cook pounds with one hand and turns the mixture with a spoon in the other. The clay mortar and wooden pestle bruise the vegetables just enough to soak up the sour, salty, sweet and spicy dressing while staying crunchy. A heavy granite set would pulp them.

The bowl's porosity is also why cleaning matters. Clay that has held fish sauce, garlic, lime juice or fermented fish sauce (pla ra) will hold onto those aromas if it is not rinsed promptly.

Why Does a Clay Mortar Need Gentler Cleaning Than Stone?

A clay mortar needs gentler cleaning than a granite mortar because unglazed clay is softer, more porous and more brittle. Three things follow from that:

• It absorbs liquids. Soap, dish detergent and strong smells can soak into the walls and later transfer to food.
• It can crack. Sudden temperature changes, long soaking or a knock against the sink can cause chips or hairline cracks.
• It stays damp inside. Clay that is stored before it is fully dry can develop musty odors or mold.

The wooden pestle has the same weaknesses. Wood swells when soaked, can split as it dries, and can absorb detergent.

How to Clean a Clay Mortar and Pestle After Everyday Use

For everyday cleaning, a quick rinse and gentle scrub right after cooking is enough.

1. Empty it straight away. Scrape out leftover salad, dressing and seeds with a spoon or spatula so nothing dries onto the clay.
2. Rinse with warm water. Hold the mortar under warm, not boiling, running water. Avoid moving it from cold to very hot water quickly.
3. Scrub the inside. Use a soft brush or the soft side of a sponge. Pay attention to the base, where chili seeds and garlic bits collect.
4. Skip the soap, or use a tiny amount. Plain water and scrubbing are usually enough. If oily residue remains, use a very small drop of mild dish soap and rinse thoroughly so no soapy taste is left in the clay.
5. Wash the wooden pestle. Rinse and scrub the pounding end, where food residue builds up, then rinse the handle.
6. Shake off the water and dry. Wipe both pieces with a clean towel, then let them air-dry fully (see the drying section below).

How to Remove Stubborn Food Residue and Lingering Smells

Stubborn residue and smells in a clay mortar are best handled with gentle, food-safe abrasives such as baking soda or coarse salt, not harsh chemicals.

Dried-on food residue

If papaya shreds, tamarind pulp or sticky palm sugar have dried onto the clay, fill the mortar with warm water for a short time to loosen them. Then scrub with a brush. Keep this brief: a short soak loosens residue, but leaving the clay waterlogged invites cracking and slow drying.

Garlic, fish sauce and fermented fish smells

To freshen a clay mortar that smells of garlic, fish sauce or pla ra:

1. Mix baking soda with a little water into a thick paste.
2. Spread it over the inside of the mortar and the pounding end of the pestle.
3. Scrub gently with a brush, then rinse thoroughly with warm water.
4. Dry the pieces completely, ideally somewhere airy or in indirect sunlight.

Another option is to scrub with a pinch of coarse salt and a little water. Salt acts as a mild abrasive.

Clay will never become completely neutral. Some cooks keep one mortar for strongly fermented dishes and another for milder salads so aromas don't cross over.

Dark spots or musty patches

Fuzzy spots or a musty smell usually mean the mortar or pestle was stored while still damp. Scrub the area with baking soda paste, rinse well, and let it dry thoroughly in a warm, ventilated place. If the mold returns, or has worked into cracks you cannot clean, replace the piece.

What Should You Avoid When Cleaning a Clay Mortar?

Avoid anything that soaks, shocks or scours the clay and wood:

• The dishwasher: long exposure to hot water and detergent can crack the clay, saturate it with soap and split the wooden pestle.
• Long soaking: both clay and wood absorb water, which slows drying and weakens the material.
• Heavy detergent or bleach: porous surfaces can hold onto these and pass the taste or residue to food.
• Steel wool or harsh scouring pads: these can scratch and wear down the clay surface.
• Sudden temperature changes: pouring boiling water into a cold mortar, or rinsing a warm one under cold water, risks cracks.
• Rough handling in the sink: terracotta chips easily if it knocks against a hard basin or faucet.

How to Dry a Clay Mortar and Wooden Pestle

A clay mortar and wooden pestle should be dried completely before storage, because trapped moisture causes musty smells and mold.

1. Wipe away surface water with a clean, dry towel.
2. Set the mortar upright or tilted on a dish rack in a spot with good airflow, so air reaches the inside. If you set it upside down on a flat surface, moisture can stay trapped under the rim.
3. Lay the pestle on its side or stand it so the pounding end is exposed to air. Don't leave it standing in a puddle inside the mortar.
4. Allow plenty of time. Unglazed clay can feel dry on the surface while still holding moisture inside, so leave it out longer than you would a glass bowl.

How to Store a Clay Mortar and Pestle

Store a fully dry clay mortar and pestle in a dry, ventilated place where they won't be knocked or crushed.

• Keep air around them. An open shelf works better than a sealed cabinet, especially in a humid kitchen.
• Store the pestle beside the mortar. Standing it upright inside can trap moisture where wood meets clay.
• Protect the clay. Don't stack heavy pots or pans on the mortar, and keep it away from shelf edges.
• Keep it away from strong odors. Porous clay can pick up smells from nearby foods or cleaning products.

Clay vs. Granite vs. Wooden Mortar: How Cleaning Differs

Thai kitchens use clay, granite and wooden mortars for different jobs, and each needs slightly different care.

Mortar type	How to recognize it	Typical Thai use	Cleaning and care
Clay (krok din)	Orange-brown, matte, porous, tall and deep, lightweight	Som tam and other pounded salads; light bruising	Warm water and a soft brush; little or no soap; no soaking or dishwasher; dry thoroughly; fragile
Granite (krok hin)	Gray or speckled, heavy, cold and dense, with a thick heavy pestle	Curry pastes, chili pastes and grinding spices into smooth pastes	Tolerates firm scrubbing and handling much better; still rinse well and dry; far less likely to crack
Wooden	Warm brown wood grain, tall bowl, wooden pestle	Pounded salads, especially Lao-style papaya salad	Rinse and scrub quickly; no soaking or dishwasher; dry fully to prevent warping and splitting

If you don't own a clay mortar, a deep wooden mortar is the closest substitute for som tam. A sturdy mixing bowl and the end of a rolling pin can bruise vegetables in a pinch, but a shallow bowl lets ingredients fly out and doesn't give the same controlled pounding and tossing motion.

When Should You Replace a Clay Mortar or Wooden Pestle?

Replace a clay mortar if it has a crack through the wall, pieces chipping from the inside, or persistent mold you cannot scrub out. Cracks trap food residue and moisture, and loose bits of clay should not end up in food. Replace a wooden pestle if it splits deeply, crumbles at the pounding end or keeps developing mold. Surface stains and a darkened interior are normal signs of use and are not a reason to replace either piece.