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Understanding the Fermentation Process

The essential components of sourdough are:

  • levain (live bacteria and natural yeast culture)
  • dough (water + flour)
  • time
  • temperature

When you bring these all together, you begin this exciting process of fermentation. Let’s break it down for you:

When you add water to flour, two things happen: starch molecules in the flour expand, and gluten molecules team up to form long, curly chains that bond together to create a network of gluten. This network lends a stretchy quality to the dough and allows it to trap gas - think of it like a balloon that stretches and swells with air. Now where do these gases come from? We're glad you asked!

Sourdough levain is the live stable culture of lactic acid bacteria and natural yeast in a mixture of flour and water. This culture feeds on the flour, and in this digestive process the yeast produces gas (CO2) which leavens the dough (inflates it with gas). The lactic acid bacteria produces lactic acid, which give us that sour flavour we love, and releases sugars to further flavour the dough and caramelizes the crust.

Time plays an important role in this process. Gluten can form from mixing or naturally by itself over time. The quicker you want to develop it, the more mixing you need. But time can also accomplish the same thing - just let the dough rest and the bonds form by themselves. The more time passes, the more the bacteria reproduces and releases acids, gas and sugars into the dough. This contributes to the swelling of the dough and richer and more complex flavours.

Temperature is another variable. The warmer the dough, the faster the digestive process occurs - the yeast and bacteria go into a frenzy. The colder it is, the slower yet more thorough this process is. Combine and introduce the dough to colder temperatures for an extended period of time, and the result is a slow, natural leavening of the dough.

In other words, the dough is slowly getting digested by the bacteria which is a sort of pre-digestive process for you. More gas, acids and sugars are being released into the dough, which translates to more flavourful and crusty breads. Of course, there is a limit to this sort of thing. If you give the dough too much time, the bacteria will consume it all and turn to liquid. The gluten breaks, the gas releases and the dough deflates - this is what we call over proofing.

The baker’s job is to find the balance of time and temperature, with the right amount of culture/levain and combination of water and flour - and it's no small feat! But when done correctly, you end up with a darker, golden mahogany coloured crust, a flavourful crumb and a loaf that stays fresh for days.