Understanding the language of sourdough bread

Bread making begins when flour is mixed with water to create a dough. When flour is hydrated, the proteins in the flour, specifically glutenin and gliadin, begin to form gluten. Gluten is a viscoelastic network that can be imagined as a spider web of gluten strands that hold the dough together. As the dough is worked and kneaded, the gluten strands are uncoiled, and become stronger and more elastic, which trap the byproducts of fermentation happening from the yeast. As the dough is exposed to heat, the pockets of trapped CO2 expand and burst, creating those holes you see in your loaf, resulting in a nice, airy crumb.

The wild yeast present in sourdough contains a whole gang of different yeasts, and is mainly populated into your sourdough starter from the surrounding environment, and any yeasts already naturally present in the flour. This allows for a hyperlocal collection of yeasts that can lend their unique flavour characteristics into your loaf. 

All of these yeasts and bacteria are cultivated in your sourdough starter, which is “fed” with flour, which the yeast and bacteria feed upon. After a while, you’ve nurtured a hearty colony of yeasts and bacteria that is active and strong enough to be used to bake bread with.

The hyperlocality of the bacteria can be so drastic, that scientists once embarked on a study of the microbes in the air of San Francisco, where their sourdough was deemed especially delicious. They found a species of acid bacteria called Lactobacillus sanfranciscensis (recently renamed Fructilactobacillus sanfranciscensis), a previously uncatalogued bacteria that marked the loaves and starters of San Francisco.

Although yeast plays an important role, the symbiotic relationship between the wild yeasts and lactobacteria is the driving force in the fermentation process. Water is a key component for both yeast and bacteria to begin predigesting the carbohydrates in the flour, and the yeast enzymes break down the starches, turning them into sugars. 

The interesting thing about the wild yeast is that it’s unable to naturally process the sugar, but the lactobacillus can. The ultimate result is that it produces carbon dioxide and ethanol, of which the bacteria uses to produce lactic acid. The compounded effect of this fermentation comes in the form of structure and flavour, and also creates the ideal environment for the yeast that’s inhospitable to other organisms, which is how sourdough starters are able to be kept alive perpetually without it spoiling. The acidity present in the bread also then acts as a preservative, even after baking.

The two proteins in flour—gliadin and glutenin—are only activated to form gluten when hydrated. Combined, this is what forms gluten, the foundation of your loaf’s structure. 

If your yeasts and bacteria are your building materials, gluten would be your scaffolding. This is why there is a distinction between normal all purpose flour, and bread flour, which possesses a higher percentage of protein. Kneading the dough strengthens the gluten network, which acts as an elastic, sticky balloon that retains the gases produced from the fermentation, and in turn, is what gives your loaf a nice crumb, which can be determined by the holes in your loaf. Without a good gluten network, the bread will not rise due to all the gases escaping, leaving you with a dense brick. 

When the dough is stretched, folded, divided, and shaped, the air pockets are redistributed or collapsed entirely. The yeast will continue to ferment and produce by-products, and the bread will rise again as carbon dioxide is captured in the gluten network. 

The development of gluten appreciates with time, and allows for a healthier loaf, as it allows the gluten to break down into amino acids that are easier to digest, which is why some people who are usually sensitive to gluten are able to tolerate sourdough bread. 

Reading the crumb of your baked loaf can also be an extremely helpful indicator of what went wrong throughout your baking process, whether it’s issues with your fermentation, heat, hydration, and everything in between. In this case, sourdough is truly an open book.

When the dough is exposed to heat and baked, the gases produced during the kneading and fermentation processes expand, and cause the bread to rise. The expansion of the gases are due to the higher kinetic energy present in the gases, based on the basic laws of thermodynamics. The ‘oven spring’ is what bakers look for in a good loaf of bread, and it is one of the first signs once it's in the process of baking that can give you an indication on the success of your loaf.

The heat from the oven also allows the starch in the flour to absorb the water and gelatinise, and changes the texture of the dough into the familiar structure of what you know as bread. The crust forms as the water is evaporated from the outer layer of the dough due to its direct exposure to heat, and acts as a barrier to prevent the inside of the bread from drying out.

The beautiful designs on a loaf of bread are also not there just for decorative purposes, but rather allows the trapped gases a determined escape route to ensure consistent shapes for all your loaves. It also gives bakers a signature design for each loaf to distinguish them, and gives the revered ‘ear’ of a loaf for additional texture.

Whilst this isn’t the full, comprehensive breakdown of the intricate workings of sourdough, it’s certainly more than enough to allow one to appreciate their next loaf of sourdough a little bit more. 

The incredible science for a food as ancient as sourdough bread gives way to a new level of appreciation for the alignment of stars that allows us to enjoy a food item that has been minimally changed since its conception. 

Slowing down, using your hands, and devoting yourself to understanding the character of each loaf, to feel it, to sense its needs, can be a magical thing.

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