Machine Production of Xiaolongbao and Soup Dumplings: Aspic Filling and Pleats

Xiaolongbao (小籠包) and soup dumplings (湯包) are among the filled snacks that test machines the most. Thin wrappers, many pleats, and plenty of soup work against each other: the thinner the wrapper, the more easily it tears, and the more soup, the more easily it leaks. Before mechanizing, first understand where the soup comes from.

Where the Soup Comes From: Aspic

The soup in xiaolongbao comes from "aspic" (皮凍) mixed into the meat filling. Aspic is made by simmering pork skin (or chicken feet or bones) for a long time to release the gelatin, which sets into a jelly as it cools. When wrapping, it is solid; when steamed, it melts in the heat and becomes the soup inside the wrapper.

This property determines everything about machine production: aspic is solid only when cold. As soon as the filling warms up, the aspic starts to soften and release liquid, and the filling goes from "extrudable and cuttable" to "runny and leaky."

What to Watch for When Running Soup Filling (Aspic) on a Machine

1. Keep the filling cold: After mixing the aspic and meat filling, refrigerate it and keep it as cold as possible on the machine; some lines keep the hopper or work area cool. In summer, as working time stretches out and the filling temperature rises, the leakage rate climbs noticeably.
2. Chop the aspic finely and mix evenly: Large chunks of aspic make metering inaccurate, so one dumpling ends up with lots of soup and another with little.
3. Wrapper strength: Xiaolongbao wrappers are thin, but they need enough gluten strength to hold the filling and survive steaming. Both the dough recipe and resting time need adjusting.
4. Secure sealing: If the seal does not close tightly, soup bubbles out of the top during steaming.
5. Wrapper-to-filling ratio: A machine's strength is that it can fix the wrapper and filling weights, but the best ratio must first be found during test runs.

How Many Pleats Can Machines Make?

Handmade xiaolongbao are often held to the exacting standard of "18 pleats," but that is a hand-making convention, not a machine specification. A machine's pleats depend on the design of its sealing mechanism or pleating unit:

• Some models twist radial pleats directly during sealing.
• Others connect a separate pleating unit. In its description of xiaolongbao, RHEON's Japanese website lists an encrusting machine paired with a "Chinese-style steamed bun pleating machine" (中華まんヒダ付け機), equipment that adds pleats to the tops of formed products.

Exactly how many pleats can be pressed, and how deep, varies by model. You need to see the actual machine or test samples; it cannot be summed up in a single number.

Which Models Suit Soup Dumplings?

Machines that make xiaolongbao and soup dumplings are usually encrusting and forming machines. When choosing a model, look at:

• Whether it can handle soft fillings containing solid particles: Aspic filling changes in firmness as the temperature fluctuates.
• Whether the wrapper can be adjusted thin enough: Xiaolongbao wrappers are much thinner than ordinary steamed buns.
• The sealing and pleating mechanisms: These determine the appearance.
• Cleaning: Meat filling with aspic is very sticky, so the hopper and feed tubes must be easy to disassemble and wash.

The products listed for the KN551 on RHEON's U.S. website include Soup Dumplings, Crystal Dumplings, and Shumai; the xiaolongbao page on the Japanese website lists models including the universal CN700, the CN601 for fermented dough, and the two-row WN155.

The products listed on Dong-Yih Machinery's website for the DY-201 Automatic Steamed Bun and Mantou Machine include xiaolongbao, with an output of 2,000–12,000 pieces/hour. For soup dumplings and large soup dumplings with a higher proportion of soup, we recommend a test run with your own wrappers and filling, or call 06-257-4644.

Frozen Xiaolongbao

Frozen xiaolongbao must be frozen before the aspic melts, so the sooner they go into blast freezing after forming, the better. For frozen transport, Article 8 of the Regulations on Good Hygiene Practice for Food (食品良好衛生規範準則) requires that the ambient temperature of frozen compartments must not be higher than -12°C; during sale and storage, the storage temperature originally set by the manufacturer must not be changed (Article 27 of the same regulations).

For steamed bun line configuration, see Machine Production of Steamed Buns.

FAQ

Q: Will machine-made xiaolongbao leak soup?
A: Leaking is mostly related to the filling warming up, the aspic melting, or a seal that is not tight. Keep the filling cold and give the wrapper enough gluten strength, and leakage can be kept down.

Q: Can a machine make 18 pleats?
A: Eighteen pleats is a hand-making convention, not a machine specification. The number of pleats a machine makes depends on its sealing or pleating mechanism; look at samples from the actual machine.

Q: Can Dong-Yih's machines make xiaolongbao?
A: Dong-Yih's website lists xiaolongbao among the products the DY-201 can make. For soup dumplings with a high proportion of soup, we recommend bringing your ingredients for a test run.

Q: How is aspic added to the filling?
A: The common method is to let the aspic cool and set, chop or grind it, and mix it into cold meat filling, keeping everything cold throughout.

Q: What is the difference between xiaolongbao and soup dumplings?
A: Usage varies by region. Generally, xiaolongbao are smaller with slightly thicker wrappers, while soup dumplings often refer to products with a higher proportion of soup and thinner wrappers.