Physicists say industrial bread dough kneaders need a redesign

New research suggests the design of industrial bread dough kneaders don't reflect the physics of bread making.

High quality bread requires just the right amount of kneading, which works air into the dough. Air develops the dough's gluten network, which provides the bread structure. Too much kneading, however, can curb the dough's ability to absorb water, yielding a dense, tight bread that doesn't rise. Not enough needing and the bread won't be able to retain gas.

For the new study, published this week in the journal Physics of Fluids, scientists simulated the local mechanical and microstructural changes that take place during the four stages of the kneading process.

To start, scientists had to ensure their kneading model reflected the unique physical properties of bread dough, which combines the characteristics of a viscous liquid and an elastic solid.

"Because of its elasticity, dough overcomes gravitational forces during kneading and moves toward the rotating rod, then climbs up it," study co-author Natalie Germann, researcher at the Technical University of Munich in Germany, said in a news release. "If you've ever used a kneader or mixer to make dough in your kitchen, you've probably observed this phenomenon."

Using their model of bread dough physics, scientists simulated how air is worked into the dough matrix via different types of industrial kneaders. The simulations revealed the dynamics of gas exchange happening on the dough's surface and interior, and also showed how air pockets form and break up throughout the industrial kneading process.

"Previous works considered only the purely viscous properties of the bread dough and restricted their simulations to extremely simplified geometries such as a concentric cylinder setup," said Germann.

The model helped scientists understand why bread dough tends to ride up the rod of electric mixers, and also revealed ways engineers might tweak the designs of commercial dough kneaders.

"Our computer simulations showed that vertical mixing isn't as good as the radial mixing in the spiral kneader we considered in our work. In the future, mixing performance may be enhanced by using a more highly curved spiral arm or two spiral arms similar to kneading by hand," Germann said.

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