While the kitchen is very different from the controlled environment of the scientific laboratory, there is chemistry, biochemistry, and physics behind crafting the ideal baked good. Flour is the central ingredient used in baking cakes, breads, muffins, pastries, cookies, etc. A key component of flour is its protein content. When dough is made, the proteins combine when mixed with water to form gluten. Gluten gives dough its elastic and pliable nature. While chefs have mastered the art of proper mixing and gluten formation in dough, scientists have worked to understand the scientific underpinnings of this phenomenon.
Baking and Gluten
“Gluten-free-bob-brown-rice-flour” by Andrea_Nguyen is licensed under CC BY 2.0
Gluten is formed when the two proteins in flour, gliadin and glutenin, combine after being mixed with water. If mixed more, the gluten becomes more developed. Developing gluten to the proper level is essential to obtaining your desired baked good. For example, bread dough requires more mixing and kneading than cake batter does, since bread dough is more glutenous. As the flour mixture is mixed together, the network of proteins is bonded together more strongly. If the mixture is mixed thoroughly enough, this will cause dough to form. Gluten is what makes dough pliable and elastic. Further kneading and working with the dough will strengthen the gluten strands. When bread dough is kneaded, gluten strands get stronger and longer, causing the elasticity of the dough to increase. If too much gluten is formed, the elasticity is negatively impacted, causing the bread to become tough and chewy. Therefore, it is important not to over knead dough when baking. If the baker stops kneading the dough, it reduces its elasticity, causing the dough to relax. If dough is not mixed as thoroughly, this results in less gluten development as is seen when preparing pastry dough. Too little gluten development will result in pastries that easily fall apart, since gluten formation is necessary for holding the flour together. As a home baker, I am disappointed when my creations fail due to too much or too little mixing. I recently overmixed birthday cake batter, causing the gluten to over develop, leading to a streaky, gluey cake after baking. Overall, proper gluten development is absolutely essential to successful baking outcomes.
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“Chocolate Chip Cookie Dough” by Live♥Laugh♥Love is licensed under CC BY-NC-ND 2.0
“Ugandan Chapati Dough” by AdamCohn is licensed under CC BY-NC-ND 2.0
Factors Affecting Gluten Formation
A study on factors affecting gluten production and development during dough mixing was done by Abang Zaidel and Dayang Norulfairuz from the Universiti Putra Malaysia in 2007. In this study, gluten production in dough was examined in terms of the quantity and quality of gluten produced. Two types of flour, strong and weak, were used to measure gluten quantity and quality, with the strong flour having a higher protein content. They measured the quantity of gluten in terms of the amount of wet and dry gluten in the baking mixture. The wet gluten content was determined by washing the dough under running water and then weighing the gluten run off. The wet gluten was then dried using an air oven and dry gluten content was measured. The quality of gluten was examined by observing the degree to which the volume of the dough expanded when fried in hot oil. Higher quality gluten would result in more expansion of the pastry.
The Effect of Mixing Time, Salt Levels, and Water Levels on Gluten
Zaidel and Norulfairuz graphed the effects that mixing time, salt levels, and water levels had on the quantity and quality of gluten studied. The results showed that the amount of salt in the dough had the greatest effect on the gluten. It was concluded that as the salt level in the baking mixture increases, it causes the gluten content to decrease. The dough becomes less elastic when salt is added, showing that the network of gluten protein molecules is not as strong when salt is added. This may be because the salt crystals disrupt the bonds involved in the formation of the networks between the proteins. Water levels had the second greatest impact on the quantity and quality of gluten in the experiment. Although water is necessary for gluten formation, it is not the primary factor affecting gluten quantity and quality. Mixing time was found to have the least impact on gluten formation. While it is important to not over or under mix dough in the kitchen, the salt and water content in the dough have a greater impact on gluten formation.
Gluten Physics: Tensile Stress and Strain
A tensile test was performed to determine gluten extensibility and elasticity. To do this, the experimenters performed stress and strain tests on a gluten strip clamped at both ends. Using standard physics formulas, the experimenters were able to quantify the tensile strength of the gluten. They measured parameters related to gluten extensibility such as original gluten length, gluten length at fracture, measured force, and actual force acting on the gluten strips. A stress-strain curve following an exponential equation was created to depict the tensile strength of the gluten graphically.
Gliadin and Glutenin
The balance between gliadin and glutenin is central to understanding gluten function. Over the centuries, researchers have performed experiments to understand the specific properties of gliadin and glutenin. It was demonstrated in 1805 that gluten could be separated into two components based on solubility in polar aqueous 70% ethanol. By the end of the nineteenth century, the two fractions were named “gliadin” and “glutenin”. These two proteins were further characterized by their respective contents of proline and glutamic acid and the degree of amidation (the addition of an amide group to the end of the polypeptide chain) in the proteins.
Close-up of The Gliadin Polypeptide Chain
“File:Pèptids de la gliadina relevants en la celiaquia.jpg” by José Miguel Mulet is licensed under CC BY-SA 4.0
The amount of gliadin compared to glutenin in flour is an important factor to consider when examining the role of these proteins in gluten formation. Researchers in America, Australia, England, and France studied the effect that the ratio of gliadin and glutenin in flour had on gluten quality. While initial reports showed conflicting results, in 1912 it was eventually experimentally observed that a higher proportion of glutenin increases dough strength while a higher gliadin content produces weaker and inelastic gluten. However, these results were inconclusive, as the accurate identification and separation of the two proteins was not mastered at the time of the experiment. Following 1912, a century of research was dedicated to revealing the complexity of the action of gluten and its component proteins. The role of the bonds involved in the formation of the secondary structure of gliadin and glutenin in the action of gluten was studied. It was determined that bonds between the protein chains, such as hydrogen bonds and disulfide bonds, had an impact on gluten formation. Further research led scientists to believe that the effect of gliadin and glutenin ratios on dough quality is due to their different molecular sizes and their distribution in gluten. In the future, researchers may uncover more secrets surrounding the action of gliadin and glutenin in gluten formation.
There is a lot more to be learned about gluten and its molecular components. The next time you are enjoying a baked treat, remember all of the science that went into crafting it. Without science, the baked goods that we eat would not have the same texture or look. Cakes would fall flat, pastries would fall apart, and bread would be too dense. Perfecting gluten formation when making dough is essential to ideal baking outcomes. Therefore, it is important that scientists continue to investigate the underlying factors that contribute to the action of gluten.