Machine Production of Rice Balls and Filled Rice Products

Rice balls are a mainstay for convenience stores, breakfast shops, and lunch box businesses. Japanese triangular onigiri, Taiwanese glutinous rice rolls (台式糯米飯糰), and Italian arancini all share the structure of "rice wrapped around filling." The key to mechanizing rice products is how you treat each individual grain.

Can Cooked Rice Run on an Encrusting Machine?

Yes, with conditions. Encrusting machines were originally designed for continuous, extensible materials like "dough"; cooked rice is made of separate grains held together by surface stickiness and has very low extensibility.

The products listed on the website of Japan's RHEON include ohagi (おはぎ, a wagashi of glutinous rice wrapped in red bean paste or red bean paste wrapped in glutinous rice) and sekihan manju (赤飯饅頭); the product list for the CORNUCOPIA KN551 on its U.S. website includes Arancini. This shows that wrapping filling in rice is an application of encrusting machines. However, the rice in these products is mostly glutinous rice or partially pounded, stickier than ordinary white rice, with a texture different from rice balls with "distinct grains."

Will the Rice Grains Get Crushed?

Yes, and this is the biggest challenge of running rice on a machine:

• Squeezing: If an encrusting machine's feeding method applies significant pressure to the material, the grains get flattened and crushed, producing a texture like rice cake or mochi.
• Shearing: During mixing and conveying, the grains rub against each other, wearing starch off their surfaces and making them stickier and stickier.
• Temperature: Warm rice is softer and stickier, and it hardens and loses stickiness as it cools; if it sits too long, the starch retrogrades, the grains loosen, and they no longer hold together.

So for Japanese onigiri that aim for a "distinct-grained, fluffy" texture, the industry mostly uses dedicated rice forming equipment: the rice is laid into molds with lower pressure, then the filling is added and the mold closes to form the ball, squeezing the grains as little as possible. This type of rice forming machine is a different equipment category from encrusting machines.

How Are Filled Rice Balls Made?

Common approaches to mechanization:

1. Mold type: A measured amount of rice is laid into a triangular or round mold, a hollow is pressed in the center, the filling (salmon, tuna mayonnaise, umeboshi, etc.) is added, another layer of rice covers it, and the mold closes to form the ball. The outside is then wrapped with nori or packaging film.
2. Encrusting type: An encrusting machine co-extrudes rice around the filling, suited to rice products where a chewier, stickier texture is desired, such as glutinous rice products or fried rice balls.
3. Semi-manual: The rice is portioned with metering equipment, while filling and forming are done by hand.

Taiwanese glutinous rice rolls (filled with youtiao, pickled radish, pork floss) are large, with lots of filling and irregular shapes, and are still commonly shaped mainly by hand, supported by rice warming and portioning equipment.

Conditions for Running Rice on a Machine

• Rice variety and cooking: Japonica, glutinous, and blended rice differ in stickiness; water quantity and cooking method change grain firmness.
• Temperature: Rice is easiest to form within a certain temperature range; too hot and it is too soft, too cold and it is too hard. Production lines often have rice warming or cooling equipment to control temperature.
• Seasoning: Sushi rice with vinegar changes in both stickiness and acidity; seasoning should be even, and overmixing should be avoided.

Hygiene

Cooked rice is a food in which microorganisms grow easily, so storage temperature and time after forming are important. Article 8 of the Regulations on Good Hygiene Practice for Food (食品良好衛生規範準則) also regulates transport: the ambient temperature of vehicle compartments carrying refrigerated food must not be higher than 7°C. Before cleaning equipment, stop the machine, cut the power, and apply lockout/tagout in accordance with Article 57 of the Occupational Safety and Health Facilities Regulations (職業安全衛生設施規則).

None of the models listed on Dong-Yih Machinery's website indicate rice balls or rice products as suitable products. If you need to mechanize rice products, call 06-257-4644. For bar-shaped rice products, see Dividing Ningbo Rice Cakes, Korean Rice Cakes, and Bar-Shaped Rice Products.

FAQ

Q: Can white rice be wrapped directly with an encrusting machine?
A: It can, but squeezing tends to make the grains flat and sticky. For rice balls with distinct grains, rice forming equipment with lower pressure is more commonly used.

Q: Why do machine-made rice balls turn out like rice cake?
A: Usually because of excessive squeezing and mixing, which crushes the grains and wears starch off their surfaces. You can adjust feeding pressure, rice temperature, and rice variety.

Q: How is the filling placed inside triangular onigiri?
A: Commonly, rice is laid into a mold, a hollow is pressed in the center, the filling is added, and another layer of rice is placed on top before the mold closes to form it.

Q: Can glutinous rice rolls be mechanized?
A: Taiwanese glutinous rice rolls have lots of filling and irregular shapes, so they are still commonly shaped mainly by hand, supported by rice warming and portioning equipment.