How does it work?
Dough mixing can be viewed as a simple reaction in which the reactants transform into a homogeneous and aerated dough:1
Flour + Water + Air + Energy (work) → Dough
The mixed dough consists of continuous (gluten) and discontinuous or dispersed (air cells) phases. Ideally, this mechanical process creates a visco-elastic mass that has optimum dough handling properties and gas retention capacity, essential for product expansion during proofing and oven spring.
Dough formulation that fall into the “dough mixing” concept should meet the following conditions:
- Use of flour from hard wheat. All-purpose and soft/hard wheat flour blends can also be used).
- Hydration levels of 50–70% depending on the presence of bran, amount of protein and degree of starch damage in the flour.
- Flour and water (combined) usually represent more than 70% of total formula weight (rich and sweet doughs) and at least 90% of formula weight (lean doughs).
Relevance
Mixing is a crucial step in all dough systems used for the manufacture of yeast-leavened baked goods. It is critical to obtain the right rheological properties and consistency of the dough for the production process to run smoothly, as well as achieve the desired finished product quality.
- In Sponge and Dough Systems: The sponge is mixed first and then ferments. The second mix is dough mixing, where the objective is to develop the gluten.
- In Straight Dough and No Time Systems: Dough mixing happens only once.
- In Continuous Mixing Dough Systems: The first mixing is a blending step, which is not intensive in nature. The goal here is to distribute and incorporate ingredients evenly. After a set time in a fermentation and holding tank, a second mixing step occurs. This is mechanically intensive, since the goal is to develop the gluten.
Stages of dough mixing
- Pick up: dough is sticky, cold and lumpy.
- Initial development: dough gets warmer, smoother and drier.
- Clean up: dough is at maximum stiffness and comes together as one cohesive mass.
- Final development: Dough is at the correct temperature and handling quality (gluten film is visible, and the dough is ready to be discharged from mixer).
- Letdown: The gluten matrix begins to degrade. The dough is too warm and sticky, lacks elasticity and has too much flow.
- Breakdown: dough is beginning to liquefy. At this stage, the dough is not salvageable and cannot be used to make bread.
Excessive mechanical energy and shear break-down the relatively stable molecular interactions between gluten-forming proteins such as disulphide bonds (S–S). This causes depolymerization of large gluten aggregates.2
In this stage the dough becomes a fluid and viscous mass (with minimum or no elasticity) that has lost most of its water holding capacity. As a consequence, most of the retained water is released and dough becomes excessively sticky.
Relationship between mixing stages and dough status
| Mixing stage | Dough status | |
| Pick up | Dough not ready (undermixed) | Ingredients insufficiently dispersed (mixture is not homogeneous yet). |
| Initial development | Gluten-forming proteins (gliadins and glutenins) gradually become hydrated and start to develop gluten. Kneading and air incorporation initiates. | |
| Clean-up | Gluten is partially developed (too elastic and poorly extensible). | |
| Final development | Dough mixed sufficiently | Gluten fully developed. Dough has optimum handling properties and gas retention. Air cells are subdivided and re-distributed. |
| Letdown | Initial stage of overmixing | Gluten starting to become weak. |
| Breakdown | Final stage of overmixing | Gluten too weak. |
Effects of Undermixing (dough too cold):
| Dough | Finished Product |
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Effects of Overmixing (dough too warm):
| Dough | Finished Product |
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Application
Different mixers can be used in making bread dough. Capacity (pounds of dough per hour), energy consumption, rpm, acquisition costs, level of process control, hygienic design, are some features that high-speed bakers often consider buying dough mixing equipment.
- Continuous mixer
- Horizontal mixer (batch-mode operation)
- Spiral mixer (batch-mode operation)
- Tweedy or Chorleywood bread mixer (batch-mode operation)
The addition of salt, sugar and fat should be delayed to reduce dough mixing time. This helps gluten proteins hydrate and develop quickly (clean-up stage takes much less time), and provides maximum friction against mixer bowl.
Mixing is an intensive mechanical operation that produces heat from friction. This is evidenced by the temperature increase in the mass being transformed into dough. For proper machining during makeup, a final dough temperature should be close to 76–82°F (25–28°C).
To assess if the dough is properly developed, perform the gluten film test. A small portion of dough is stretched between the hands into a thin, smooth, translucent film to test its extensibility and elasticity:
References
- MacRitchie, F. “Structure and properties of dough.” Concepts in Cereal Chemistry, CRC Press Taylor & Francis Group, LLC, 2010, pp. 29–35.
- Hamer, R.J., MacRitchie, F., and Weegels, P.L. “Structure and Functional Properties of Gluten.” Wheat Chemistry and Technology, 4th edition, AACC International, Inc., 2009, pp. 153–161.