How a Steamed Bun and Mantou Machine Works: Sheeting, Filling, Sealing, and Shaping
A Bun's Journey from Dough to Steamer
A machine-made steamed bun goes through roughly these stages:
- Preparing the dough and filling
- Dough feeding (sheeting)
- Encrusting
- Sealing and cutting
- Shaping and pleating
- Panning and proofing
- Steaming, cooling, and packaging
The steamed bun and mantou machine handles stages 2 through 5; the stages before and after are connected by hand or with other equipment, depending on the size of the factory.
Sheeting: First Turn the Dough into a Consistent "Wrapper Stream"
Fermented dough is highly elastic and easily overworked, making it the hardest material for a bun machine to handle. The machine has to feed the dough continuously and gently from the hopper, forming a wrapper stream of consistent thickness.
For its CN601, designed for Chinese-style steamed buns and xiaolongbao, RHEON specifically states that it is suited to "highly elastic fermented dough" and can adjust the feed ratio of two stages according to the physical properties of the dough and filling, minimizing damage to the materials.
Dong-Yih Machinery's DY-201 Automatic Steamed Bun and Mantou Machine is designed around "a traditional technique that does not break down the dough structure." For the feeding principle, see Feeding Mechanisms.
Encrusting and Sealing
Bun machines usually encrust the same way as standard encrusting machines: the dough and filling meet at the nozzle with the dough on the outside and the filling in the middle, and the shutter below closes to pinch off the rope while gathering the dough toward the center to cover the filling; see Co-Extrusion Principle and Shutter Cutting and Sealing.
Meat and vegetable bun fillings contain water and oil and seep out more easily than bean paste, so there must be enough dough at the seal and it must be sealed firmly, or the buns will burst during steaming.
How Do Bun Machines Make Pleats?
After sealing, the top of the bun is round. There are two common ways to add pleats:
- Form a pattern during sealing: The shape of the sealing mechanism or a twisting motion leaves a pattern on top as it gathers.
- Pleat after encrusting: RHEON's pleating machine for Chinese-style steamed buns is connected after the encrusting machine and uses curved blades to create pleats like those made by hand, with an optional twist. The number of pleats can be 9, 12, 18, or up to 24.
See Secondary Forming for details.
Can One Machine Make Both Mantou and Filled Buns?
In most cases, yes. Mantou is simply a product with "dough only and no filling," and an encrusting machine can make it by setting the ratio to dough only (such as the 1:0 listed for RHEON's KASEIJIN (火星人) series).
The products the Dong-Yih DY-201 can make include meat buns, vegetable buns, red bean buns, and taro buns, as well as two-color mantou, mini mantou, and longevity peach buns (壽桃). It can also make French bread, filled bread, silver thread rolls, gua bao (割包), and silver thread flower rolls, with an output of 2,000–12,000 pieces/hour at 2.0 kW.
Note that mantou dough and bun dough often differ in recipe and firmness, so feeding and forming conditions must be reset when changing products, and the filling passages must be cleaned.
How Flower Rolls and Silver Thread Rolls Are Made
Flower rolls (花捲) and silver thread rolls (銀絲捲) are not "dough wrapping filling"; they rely on layers:
- Flower rolls: The dough is rolled into a thin sheet, brushed with oil, sprinkled with chopped scallions, and rolled into a log, which is cut into sections and then twisted or folded and pressed into a flower shape. After steaming, the layers open up one by one.
- Silver thread rolls: An outer dough sheet wraps many noodle strands as fine as threads. After cutting into sections and steaming, they tear apart into silvery strands.
- Gua bao: The dough is pressed into an oval sheet, brushed with oil, and folded in half; after steaming, it can be opened up and filled.
When machines make these products, the principle is to break down the hand movements of "sheeting, rolling, cutting, and twisting" and mechanize each one. RHEON's bread lines include a "twister" that twists dough sticks into shape, and forming tables that slit a thin dough sheet into multiple rows and then roll them up.
How each manufacturer's machines carry out these movements varies. To see how the Dong-Yih DY-201 makes silver thread rolls and silver thread flower rolls, call 06-257-4644 to arrange an on-site demonstration.
Panning, Proofing, and Steaming
The finished raw buns need to be arranged on steaming trays, with spacing left for expansion during proofing and steaming. At high volumes, an automatic panning machine is connected to reduce hand contact. The temperature, humidity, and time of proofing directly affect whether the buns rise well and whether the skin wrinkles. This is a matter of recipe and process management; the machine can only make the raw buns consistent.
Safety Reminder
Before cleaning, changing dies, or adjusting the pleating blades, always stop the machine, cut the power, apply lockout/tagout, and confirm that the blades and conveyors are completely still.
FAQ
Q: How does a bun machine make pleats?
A: A pattern is formed during sealing by the shape of the mechanism or a twisting motion, or a pleating machine creates pleats with blades after encrusting. RHEON's pleating machine offers 9 to 24 pleats.
Q: Can one machine make both mantou and filled buns?
A: In most cases, yes: set the ratio to dough only to make mantou. When changing products, reset the conditions and clean the filling passages. The Dong-Yih DY-201 can make both buns and mantou.
Q: How are flower rolls and silver thread rolls made?
A: Their layers come from sheeting, oiling, rolling, cutting, and twisting; silver thread rolls are fine noodle strands wrapped in a dough sheet. Machines mechanize these hand movements step by step.
Q: How many pieces can the DY-201 make per hour?
A: Its output is 2,000–12,000 pieces/hour, depending on product size and settings.