Characteristics of Glutinous Rice Dough (Tangyuan, Mochi) on Machines

Tangyuan, mochi, daifuku, and Ningbo rice cakes: these glutinous rice products have one thing in common, stickiness. That stickiness is the soul of their texture, but it is also the biggest headache on a machine.

Why Is Glutinous Rice Dough So Sticky?

Rice starch comes mainly in two types: amylose and amylopectin. Ordinary white rice contains both, while glutinous rice starch consists almost entirely of amylopectin. Amylopectin molecules are like a tree with many branches, and after heating and gelatinization, they form a very viscous structure, which is the source of the chewy, sticky texture of glutinous rice products.

Another characteristic of amylopectin is that it is less prone to "retrogradation and hardening," which is why mochi stays soft longer. But the surface of mochi still hardens, mainly because surface moisture evaporates. On a machine, if the dough is left exposed to air for too long, the surface dries and forms a skin, and it cracks during wrapping.

What Problems Arise on the Machine?

• Sticking to the hopper and conveyor: As soon as glutinous rice dough touches metal or a belt, it sticks, and the buildup keeps growing.
• Tails when cutting: Very sticky dough pulls out strings or tails when cut; see Misshapen Products, Lopsided Shapes, and Tails.
• Unstable weight: As more and more material builds up on the mechanism, the amount each piece receives changes.
• Surface drying and cracking: Glutinous rice dough left too long hardens on the surface and cracks during wrapping.

What Can Be Added to Improve It?

1. Anti-stick dusting powder: Most commonly, cooked powder (such as toasted glutinous rice flour, potato starch, or corn starch) is dusted onto contact surfaces and finished products so the surface does not stick. Use just enough to prevent sticking; too much makes the texture powdery.
2. Adjust the ratio of raw to cooked dough: The guo cui (粿粹) method often used for tangyuan takes part of the dough, cooks it first, and kneads it back into the raw dough, giving the dough cohesion without being too sticky to handle. The ratio must be worked out for each product.
3. Add other starches: Some recipes blend in a small amount of zailai rice flour (在來米粉) or other starches to reduce stickiness and make the dough easier to form, but the texture changes, so there is a trade-off.
4. Add sugar or oil: Mochi-type products often include sugar, which helps keep them soft; a small amount of oil can reduce sticking.
5. If food additives are used, they must stay within the scope permitted by regulations; see Using Dough Improvers, Emulsifiers, and Additives.

Some encrusting machines are designed with mechanisms for handling highly sticky materials. The N208, released by Japan's RHEON in 1986, was equipped with a "non-stick encrusting mechanism" (非粘着インクラスター), which the company says allowed sticky products that had been hard to handle, such as ohagi (おはぎ), to be wrapped without dusting flour. The product page for RHEON USA's KN551 also lists mochi ice cream as a product it can make. This shows that whether sticky materials can run on a machine also depends heavily on mechanism design.

How to Control Temperature

The stickiness and firmness of glutinous rice dough both change with temperature: warm, it is soft and sticky; cold, it hardens. In practice, keep the dough within a workable temperature range rather than letting it swing between hot and cold; cover finished dough to keep it moist so the surface does not dry out; and if the finished products are to be frozen, cool and package them as quickly as possible to prevent the surface from drying and cracking.

Dong-Yih Machinery's DY-528MS Dividing Machine is suitable for mochi, taro balls, sweet potato balls, Ningbo rice cakes, Korean rice cakes, and more. To find out whether your glutinous rice recipe can run on the machine, please call 06-257-4644.

FAQ

Q: Why does tangyuan dough stick to the machine so much?
A: Glutinous rice starch is almost entirely amylopectin, which becomes especially sticky after gelatinization and readily sticks to metal or belts.

Q: What can I add to make it less sticky?
A: Cooked powder is commonly used as anti-stick dusting; you can also adjust the ratio of raw to cooked dough or blend in a small amount of other starches, with proportions determined by actual testing.

Q: Why does the surface of mochi harden after sitting for a while?
A: Mainly because surface moisture evaporates; cover the dough and semi-finished products to keep them moist.

Q: Can mochi be made by machine?
A: Yes. Some models are designed specifically for sticky materials, and the Dong-Yih DY-528MS is also suitable for dividing mochi.