Traditional Wet Grinding of Rice with a Stone Mill: Making Thai Rice Batter

Traditional wet grinding of rice is the method of turning soaked rice into a smooth, milky batter by feeding it, together with small amounts of water, between two heavy rotating millstones. In Thailand the hand-turned stone mill is called a mo hin. Its slow, cool grinding produces a fine, fresh-smelling rice batter that is the foundation of many Thai desserts, steamed snacks and fresh rice noodles. The batter can be used thin and pourable, or drained into a soft dough, depending on the dish.

What Is Traditional Wet Grinding of Rice?

Wet grinding means milling grain while it is soaked and moist, rather than grinding dry kernels into powder. Rice that has absorbed water becomes soft and chalky in the center, so the millstones can crush it into very fine particles that stay suspended in water. The result is a white liquid that looks a little like thin cream or coconut milk.

Dry grinding, by contrast, produces a powder (rice flour) that has to be mixed with liquid later. Many Thai cooks value wet-ground rice because the particles are hydrated from the start, which gives desserts and noodles a soft, smooth bite.

What Does a Thai Stone Rice Mill Look Like?

A Thai stone rice mill is a pair of round, flat stones stacked one on top of the other, with a handle for turning the upper stone. Most are carved from grey granite or similar hard stone, with a rough, slightly speckled surface that feels cold and heavy to the touch.

The main parts of a stone rice mill

Lower stone (bed stone): stays still. It usually has a raised rim or carved lip around its edge with a channel leading to a spout, so the batter can run out.
Upper stone (runner stone): rotates on top of the lower stone. Its weight provides the grinding pressure.
Feed hole: an opening in the upper stone where the soaked rice and water are spooned in.
Central pivot: a peg or pin that keeps the upper stone centered as it turns.
Handle: a wooden stick fixed into the side or top of the upper stone, turned by hand in a steady circle.
Grinding surfaces: the faces where the two stones meet, often cut with shallow grooves that pull the rice outward from the center while crushing it.

When the mill is working, the white batter seeps from between the stones, gathers in the rim and trickles out of the spout into a bowl or bucket placed below. The sound is a low, gritty rumble that softens as the rice breaks down.

Which Rice Is Used, and Why Must It Be Soaked?

Thai cooks wet-grind both ordinary (non-glutinous) white rice and glutinous (sticky) rice, choosing the type according to the dish. Ordinary rice gives a batter that sets soft but holds its shape, while glutinous rice gives a stretchier, chewier result.

Non-glutinous white rice: used for batters for coconut-rice pancakes, steamed cups and fresh rice noodles. Many cooks prefer older, well-dried rice for sweets because it tends to give a firmer, less sticky texture than freshly harvested rice.
Glutinous rice: opaque, bright white kernels that become very sticky when cooked. Its wet-ground dough is used for chewy sweets and dumplings.

Soaking is essential because dry rice is too hard to grind finely on stone with water. Soaked rice swells, turns opaque and can be crushed between the fingers into a chalky paste. Cooks commonly soak rice for several hours or overnight in clean water, then rinse and drain it before grinding. A kernel that still has a hard, glassy center needs more soaking time.

How to Wet-Grind Rice in a Stone Mill, Step by Step

Wet grinding with a stone mill is a slow, rhythmic process: small amounts of soaked rice and water go in, and a fine batter flows out.

Wash the rice. Rinse it in several changes of water until the water runs mostly clear, removing dust and loose starch.
Soak the rice. Cover it generously with clean water and leave it until the kernels are soft enough to crush between your fingers.
Clean and wet the millstones. Rinse both stones so no old batter or grit remains, and set a clean container under the spout.
Drain the soaked rice. Keep some fresh water nearby to add during grinding.
Feed a small spoonful at a time. Spoon soaked rice into the feed hole with a little water. Overfilling makes the stones skid and leaves coarse pieces.
Turn the handle steadily. Rotate the upper stone in an even circle. A steady pace keeps the batter cool and the texture consistent.
Adjust the water as you go. If the batter comes out thick and pasty or the handle feels heavy, add a little more water. If it runs very thin and watery, add rice with less water.
Collect and check the batter. Rub a drop between your fingertips. It should feel smooth, with no noticeable grit. Gritty batter can be passed through the mill a second time.
Finish with the stones. Pour a little water through the empty mill to flush out the last batter into the container.

What Should Stone Mill Rice Batter Look, Feel and Smell Like?

Good stone mill rice batter is bright milky white, smooth between the fingers, and smells clean and lightly sweet, like freshly cooked rice. Batter made from glutinous rice tends to look more opaque and feel slightly heavier.

Color: pure white to off-white. A grey tint can come from dirty stones or unwashed rice.
Texture: silky, without sand-like particles. When left to stand, the starch settles into a dense white layer at the bottom with clearer water above; this is normal and simply needs stirring.
Batter consistency: for pourable dishes it should flow freely off a spoon, roughly like coconut milk or thin cream. Each recipe then adjusts the thickness with water or coconut milk.
Aroma: fresh and mild. A sharp, sour smell means the rice or batter has started fermenting, which is wanted for some noodles but not for most sweets.

How Is Wet-Ground Rice Batter Used in Thai Food?

Wet-ground rice batter is used in two main forms in Thai cooking: as a thin liquid batter that is poured and cooked, and as a drained wet dough that is kneaded and shaped.

Pourable rice batter

The liquid batter is usually mixed with coconut milk, sugar or salt and then steamed, griddled or baked.

Khanom krok: small round coconut-rice pancakes cooked in a dimpled cast-iron pan. They have crisp golden edges, a soft, almost custardy center and a rich coconut aroma. The fine, smooth rice batter is what gives the creamy middle.
Khanom tuay: little steamed cups with a sweet bottom layer, often tinted green with pandan, under a salty-sweet white coconut cream topping. The rice batter helps both layers set softly.
Steamed rice sheets and dumpling skins: thin batter spread on cloth over steam forms translucent, slippery sheets used for wrapped snacks and noodles. These are often combined with other starches such as tapioca.

Drained wet rice dough

To make dough, the batter is poured into a cloth bag and the water is pressed or hung out until a soft, damp white mass remains.

Khanom jeen (called khao pun in Isan and Laos): soft, round white rice noodles served with curries. Traditionally the rice is soaked long enough to ferment slightly, giving the noodles a gentle tang. After grinding and draining, the dough is partly cooked, kneaded and pressed through a perforated mold into boiling water.
Glutinous rice dough sweets: drained wet-ground sticky rice makes a smooth, elastic dough for chewy balls and dumplings, such as those served in warm coconut milk.

Stone-Ground Batter vs Blender Batter vs Packaged Rice Flour

A stone mill is not the only way to make rice batter, but each method gives a slightly different result. The table below compares the common options for home cooks.

Method	How it works	Typical result	Limitations
Stone rice mill (traditional wet grinding)	Soaked rice and water crushed slowly between heavy millstones	Fine, fresh-tasting batter; grinding stays cool	Slow, physically tiring, needs a mill and space; stones must be cleaned well
High-speed blender	Soaked rice blended with water at high speed	Convenient fresh batter, suitable for many home recipes	Can leave fine grit unless blended long and strained; long blending warms the batter
Packaged dry rice flour	Factory-milled flour mixed with water at home	Fast and consistent; widely available	Lacks the fresh rice aroma; absorbs water differently, so recipes written for wet-ground batter may need adjusting; no natural fermentation for khanom jeen

Tip for substitutes: if you use a blender, work in small batches, add water gradually, and pour the batter through a fine sieve or cloth to catch coarse bits. If you use packaged flour, choose the correct type: regular rice flour for non-glutinous recipes and glutinous (sweet) rice flour for sticky, chewy recipes. The two are not interchangeable.

Common Problems in Wet Grinding and How to Fix Them

Most wet grinding problems come from under-soaked rice, the wrong amount of water, or feeding the mill too quickly.

Gritty batter: the rice was not soaked long enough or was fed too fast. Grind more slowly or pass the batter through the mill again.
Handle is hard to turn: too little water. Add a splash with the next spoonful of rice.
Batter is very thin: too much water. Let it settle and pour off some clear water from the top, or drain it in a cloth bag.
Unwanted sour smell: the soaked rice or batter was left too long, especially in hot weather. For sweets, grind and use the batter promptly or keep it chilled.
Grey or speckled batter: the stones or rice were not clean. Wash both thoroughly before starting.

How to Care for the Millstones After Grinding

Millstones should be cleaned right after wet grinding, because leftover batter dries hard in the grooves and can spoil or sour the next batch.

Flush the mill with clean water while turning the handle.
Lift off the upper stone and scrub both grinding surfaces with a stiff brush, paying attention to the grooves and the spout channel.
Rinse well and let the stones dry completely in the air before stacking them again.

With clean stones, well-soaked rice and patient, steady turning, the stone mill turns simple grains into the soft white batter behind many of Thailand's best-loved sweets and noodles.