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The science of dough

Oct. 14, 2006
By Deborah Halber/MIT
and World Science staff

Trev­or Shen Kuan Ng rolls dough. He al­so stretches it like Sil­ly Put­ty, twirls it like taf­fy and flat­tens it in­to rect­an­gles like wide fet­tuc­ci­ne. 

But Ng does­n’t run a bak­er­y. A grad­u­ate stu­dent at the Mas­sachu­setts In­sti­tute of Tech­nol­o­gy, he is stu­dy­ing dough for his Ph.D. the­sis. Cor­po­rate ed­i­bles gi­ant Kraft Foods Inc. is fund­ing his work as part of an ef­fort to im­prove dough. 

Ng (Courtesy MIT/Donna Coveney)
Mom-and-pop bak­ers de­vel­op an in­tu­i­tive feel for the squi­shy sub­s­tance the tra­di­tion­al way—by hand-knea-d­ing it. But that’s out of the ques­tion for mass-pro­du­cing me­ga-ba­k­er­ies. They need a sci­en­tif­ic way to mo­n­i­tor qual­i­ty. 

They can get that by ob­tain­ing nu­mer­i­c­al mea­sure­ments of a ma­te­ri­al’s pro­p­er­ties dur­ing ma­n­u­fac­tur­ing, Ng said.

Ng’s the­sis con­cerns dough’s me­chan­i­cal prop­er­ties and be­ha­vi­or when sub­jec­t­ed to va­r­i­ous for­c­es. In en­gi­neer­ing-speak, this is called rhe­ol­o­gy. It pro­vides va­l­u­a­ble in­for­ma­tion for com­pa­nies that need re­li­a­ble tech­niques to en­sure the tas­ti­est pro­d­uct, he ex­p­lained.

Dough is one of a class of un­u­su­al ma­te­ri­als called non-New­to­ni­an flu­ids, whose vis­cos­i­ty, or slip­per­i­ness, chan­ges with the am­ount of strain on them. Ma­ny have mi­cro­scop­ic struc­tures that af­fect how they re­act when poked or prod­ded, and how fast they flow. Pic­ture pea­nut but­ter or may­on­naise drip­ping from a tap: they would­n’t be­have like wa­ter. 

Some non-New­to­ni­an flu­ids such as poly­mers bounce like a ball if dropped, but flow smooth­ly if placed on a sur­face.

Ng’s work ar­e­a con­tains a va­ri­e­ty of dough-ma­nipulating de­vices. A ma­chine known as mixo­graph twists the dough around met­al pins the way saltwa­ter taf­fy is spun in a can­dy shop. An­oth­er, the fil­a­ment stretch­er, pulls dough un­til it snaps. 

Ng works with small sam­ples of flour ground from grains new­ly de­vel­oped by farm­ers and food en­gi­neers. He records how the re­sult­ing dough is treated and how it re­acts to ma­nip­u­la­tion. Dif­fer­ent blends of flour, wa­ter and ad­di­tives can pro­duce dras­ti­cal­ly dif­fer­ent dough. At­mos­pher­ic con­di­tions and time of day al­so can af­fect the elas­tic­i­ty and rise.

The work can be tax­ing. The dough “sticks to pret­ty much eve­ry­thing oth­er than the things you want it to stick to,” the young re­search­er said. 

Ng was­n’t al­ways cut out for dough. He ar­rived at MIT with a mas­ter’s de­gree in aer­o­nau­ti­c en­gi­neer­ing from Cam­bridge Uni­ver­si­ty in Eng­land. He was plan­ning to de­sign air­plane en­gines, which are de­signed with air flow in mind. 

Ng switched to “fluid me­chan­ics of a dif­fer­ent sort,” he said, when he heard that Gar­eth Mc­Kin­ley, a pro­fes­sor of me­chan­i­cal en­gi­neer­ing, needed a dough ma­n. It sounded like some­thing “dif­fer­ent and fun,” he said. 

Glu­ten gives dough its dis­tinc­tive elas­ti­ci­ty. Glu­ten, one of the larg­est pro­tein mo­le­cules on Earth, is one of a type of pro­teins that form an en­tan­gled ma­trix whose qual­i­ty, shape and dis­tri­bu­tion with­in dough are key to its bread-making qual­i­ties. 

“The tex­ture of bread—the chewi­ness and mouth feel—is de­pend­ent on the dough you start with,” Ng said. “The airiness of the bread, or, from a com­mer­cial point of view, the amount of air they sell you, is di­rect­ly re­lat­ed to the abil­i­ty of the dough to re­sist rup­ture dur­ing the de­for­ma­tion pro­cess as it rises. When bread is in the ov­en, air bub­bles with­in the dough ex­pand. At some point they break, and the bread stops ex­panding.”

Won­der Bread, Ng said, is “a very airy prod­uct.” 

Ng does­n’t usu­al­ly eat his ex­per­i­ments be­cause the lab­o­ra­to­ry dough is cov­ered with sil­i­cone oil to keep it from dry­ing out. But since start­ing this line of re­search in 2003, Ng has be­come a home bak­er. When he bakes bread, he brings a bit of the dough in for test­ing. White bread, he said, is his fa­vor­ite.

* * *

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Trevor Shen Kuan Ng rolls dough. He also stretches it like Silly Putty, twirls it like taffy and flattens it into rectangles like wide fettuccine. But Ng doesn’t run a bakery. A graduate student at the Massachussets Institute of Technology, he is studying dough for his Ph.D. thesis. Corporate edibles giant Kraft Foods Inc. is funding his work as part of an effort to improve dough. Mom-and-pop bakers develop an intuitive feel for the squishy material the traditional way—by hand-kneading it. But that’s out of the question for mass-producing mega-bakeries. They need a scientific way to monitor quality. They can get that by obtaining numerical measurements of a material’s properties during manufacturing, Ng said. Ng’s thesis concerns the mechanical properties of dough and how it behaves when subjected to various forces. In engineering-speak, this is called rheology, and it provides valuable information for companies that need reliable techniques to ensure the tastiest product, he explained. Dough is a member of a class of unusual materials called non-Newtonian fluids. Their viscosity, or slipperiness, changes with the amount of strain on them. Many have microscopic structures that affect how they react when poked or prodded, and how fast they flow. Picture peanut butter or mayonnaise dripping from a tap: they wouldn’t behave like water. Some non-Newtonian fluids such as polymers bounce like a ball if dropped, but flow smoothly if placed on a surface. Ng’s work area contains a variety of dough-manipulating devices. A machine known as mixograph twists the dough around metal pins the way saltwater taffy is spun in a candy shop. Another, the filament stretcher, pulls dough until it snaps. Ng works with small samples of flour ground from grains newly developed by farmers and food engineers. He records how the resulting dough is treated and how it reacts to manipulation. Different blends of flour, water and additives can produce drastically different dough. Atmospheric conditions and time of day also can affect the product’s elasticity and rise. The work can be taxing. The dough “sticks to pretty much everything other than the things you want it to stick to,” Ng said. He wasn’t always cut out for dough. He arrived at MIT with a master’s degree in aeronautical engineering from Cambridge University in England, and planning to design airplane engines. Those are designed with air flow in mind. Ng switched to “fluid mechanics of a different sort,” he said, when he heard that Gareth H. McKinley, a professor of mechanical engineering, needed a dough man. It sounded like something “different and fun,” he said. Gluten gives dough its distinctive elastic behavior. To engineers, gluten is a nanoscale bio-macromolecule, one of the largest protein compounds on earth. These proteins form an entangled matrix whose quality, shape and distribution within the dough are intrinsically linked to its bread-making qualities. “The texture of bread--the chewiness and mouth feel--is dependent on the dough you start with,” Ng said. “The airiness of the bread, or, from a commercial point of view, the amount of air they sell you, is directly related to the ability of the dough to resist rupture during the deformation process as it rises. When bread is in the oven, air bubbles within the dough expand. At some point they break, and the bread stops expanding.” Wonder Bread, Ng said, is “a very airy product.” Ng doesn’t usually eat his experiments because the laboratory dough is covered with silicone oil to keep it from drying out. But since starting this line of research in 2003, Ng has become a home baker. When he bakes bread, he brings a bit of the dough in for testing. White bread, he said, is his favorite.