science of sourdough bread fermentation chemical reactions processes scientific names and latin

Explain From a Scientific Perspective: What Chemical Reactions and Processes Happen When Making Sourdough Bread?

The fabrication of sourdough bread, a gastronomic staple cherished across cultures, commences with a multifaceted dance of biochemistry and microbiology processes. It transpires in a series of biochemical transformations, influenced by a symbiotic consortium composed of Saccharomyces cerevisiae (baker’s yeast) and a genus of bacteria from the Lactobacillus family (lactic acid bacteria).

A comprehensive description of this complex art form, using Latin and scientific naming conventions, is as follows:

Creating the ‘Sourdough Starter’ (Consociatio Fermenti): The initial operation involves the establishment of a sourdough starter, colloquially known as leaven. This is an environment conducive to microbial activity, consisting of a medley of flour (Triticum aestivum) and water (H2O). Exposing this mixture to the surrounding environment encourages the spontaneous accumulation and growth of naturally-occurring yeasts and bacteria, forming a symbiotic community. This instigates a biochemical process known as spontaneous fermentation.

Autolysis (Autolysis): Once the leaven demonstrates active signs of biological activity (usually after approximately a week), it’s amalgamated with additional flour and water. This blend is then allowed to rest during a period of autolysis. During this stage, the water imbues the flour particles, activating native enzymes – amylases and proteases – within the flour. These enzymes proceed to degrade the flour’s complex carbohydrates, such as starch (Amylum), into simpler sugars (Monosaccharides) and break down proteins, namely glutenin and gliadin, into smaller peptides and amino acids.

Kneading and Fermentation (Mixtura et Fermentatio): Following autolysis, salt (NaCl) is added to the dough, which is then manually manipulated in a process known as kneading. At this point, the dough commences its initial fermentation, often referred to as ‘bulk fermentation’. The Saccharomyces cerevisiae in the leaven metabolizes the simple sugars resulting from starch breakdown into carbon dioxide (CO2), ethanol (C2H5OH), and thermal energy through a process referred to as alcoholic fermentation. The chemical reaction underlying this process can be described as: C6H12O6 → 2 C2H5OH + 2 CO2. In parallel, the Lactobacillus bacteria execute lactic acid fermentation, transforming simple sugars into lactic acid and additional carbon dioxide. This process, while generating the unique sour note characteristic of sourdough bread, also acidifies the dough, thereby deterring the proliferation of potentially harmful bacterial strains.

Proofing (Testatio): Post primary fermentation, the dough is fashioned into the desired form and allowed to undergo a second fermentation, colloquially referred to as proofing. Here, the yeast continues its metabolic journey, producing even more carbon dioxide. The gas becomes entrapped within the extensive gluten network, which was established during the kneading process, causing the dough to inflate and rise.

Baking (Coctura): After ample proofing, the dough is ready for the final transformative stage – baking. The application of heat brings about the expansion of trapped carbon dioxide and evaporation of ethanol, both contributing to the ‘oven spring’ or final inflation of the bread. Moreover, the thermal energy causes denaturation and subsequent reformation of the proteins within the dough, leading to a rigid, stable structure. Concurrently, the Maillard reaction, a non-enzymatic browning process, takes place between the amino acids and simple sugars on the dough’s surface, contributing to the enticing, golden-brown crust and enhancing the flavor profile of the bread.

Cooling and Staling (Refrigeratio et Staling): Post-baking, the bread loaf is left to cool, permitting moisture to evenly disperse throughout the bread. Over subsequent days, a process referred to as ‘staling’ commences, where the starch molecules re-crystallize and the loaf progressively loses moisture, resulting in an altered texture.

The creation of sourdough bread is a fine orchestration of biological, chemical, and physical principles, acting upon a simple combination of ingredients to metamorphose them into a complex and varied gastronomic delight. Each phase in this process, with its unique transformations, contributes to the final taste, texture, and visual aesthetics of the sourdough bread. Mastery of these stages enables the production of a wide variety of bread characteristics.

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