Culinary Science: Dough chemistry
The simple science behind one of the world’s oldest recipes
Humans have been baking bread for a long time, with some scholars suggesting it existed in a primitive fashion at least 30,000 years ago. By the time of the ancient Egyptians bread was not much different than it is today. Both the basic ingredients of flour, yeast, water and salt, and the process of kneading, rising and baking, have remained largely unchanged for thousands of years.
The molecular star of this staple food item is a protein complex called gluten. After grains such as wheat, rye or barley are milled into a flour they retain groups of proteins called glutenins and gliadins. When water is added to the flour, these proteins are able to mix and form multiple types of bonds, including disulphide bonds. Gluten is the product of this cross-linking process between glutenins and gliadins, and its special properties create a light, fluffy loaf.
In dough, gluten forms a lattice of interlinked strings of protein, making it both strong and flexible. The result (when the dough is well mixed) is a viscoelastic structure. This describes a material that is strong enough to resist some force but also elastic enough to return to its original dimensions once it has been stretched. This attribute is key to permitting bubbles of gas to form and expand within the dough, as the gluten lattice will readily move aside for expanding bubbles but won’t collapse while doing so. This means that plenty of gas can be stored and during baking will expand, producing a large, light loaf of delicious bread.
Inside the baking process
Uncover the chemistry involved in making bread – and why you shouldn’t skip out on kneading
Although nothing in the world of baking can be called a perfect science, the harmony of gluten and yeast in the bread-making process is likely one of the closest examples. Yet despite their importance in making an ideal loaf, there is a growing consumer demand for doughs that avoid using either gluten or yeast.
To contemplate omitting one of these ingredients we first have to consider what role they perform in a traditional dough. Yeast is a single-celled organism that produces carbon dioxide as it grows, adding valuable gas into the dough and helping it to rise. A substitute for this process is to rely on baking soda, which releases gas via a chemical process. Gluten is a little trickier to replace, as the protein lattice has near-perfect properties for supporting bubbles of gas. Thus, most gluten-free breads retain less gas and are denser than traditional bread.
This article was originally published in How It Works issue 116, written by James Horton
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