Wild sourdough (wild fermentation) is the traditional method for making sourdough, just like bakers have done so for many centuries. The flour contains naturally occurring microorganisms (bacteria and yeast) that ferment the dough by digesting starches and sugars in the flour, producing gas and enzymes. Phytates in the flour (which usually prevent your body from absorbing all the nutrients in the bread) are broken down by these microorganisms and gluten (glutenin and gliadin) are pre-digested and bond together in a web-like structure that traps the gas produced during fermentation, which makes the dough rise. As a result of this fermentation process, many people who are sensitive to gluten can consume fermented sourdough bread - however if you are gluten intolerant, or coeliac (allergic to gluten) please check with your health professional first.
Established sourdough starter is a symbiotic, stable culture of around 35 microorganisms - lactic-acid bacteria (LAB) and yeasts - living in a flour and water medium.
Lactic-Acid Bacteria (LAB) in Sourdough
Also known as lactobacilli, these bacteria are aero-tolerant anaerobes, which don't require oxygen but most can grow when oxygen is present. LAB metabolise sugar (glucose) in the flour, producing lactic acid which creates the classic tangy, complex flavour of sourdough bread and increases the pH to 3-4, which drops the glycemic index to under 50 (making it low GI, around half the GI of commercial yeasted bread) and the pH is also the reason why sourdough bread lasts for many days without spoiling like commercial mass-produced bread.
Group A LAB
  • homofermentative - they convert 1 glucose molecule (C6H12O6) into 2 molecules of lactic acid (2 CH3CHOHCOOH)
  • cannot tolerate oxygen
  • grow in warm temperatures (up to around 45 degrees Celsius), not at 15 degrees Celsius
  • i.e. L. delbrueckii, L. acidophilus
Group B LAB
  • heterofermentative - they convert glucose into lactic acid and acetic acid
  • can tolerate oxygen
  • grow at 45 degrees Celsius and 15 degrees Celsius
  • i.e. L. casei, L. plantarum
Group C LAB
  • heterofermentative - they convert glucose into lactic acid, acetic acid and carbon dioxide
  • i.e. L. fermentum, L. brevis, L. kefiri, L. sanfranciscensis
Yeasts in Sourdough
Wild yeasts are found in the grain bran, which is why the freshest ground flour is the best for making sourdough bread. These yeasts metabolise by-products of LAB fermentation and make carbon dioxide (gas) which causes the bread to rise.
  • convert LAB by-products into carbon dioxide (CO2)
  • i.e. kazanchastinia exigua (saccharomyces exiguous), candida milleri, candida humilis

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