To replace the baker’s yeast that most breads need to rise, sourdough requires some starter – a self-sustaining fermentation of flour, water, wild yeasts and bacteria that produce lactic and acetic acids. You might be able to get some starter from a local baker, or you can make your own – by combining small equal quantities of water and flour and letting it ferment for around five days find here.
Once you have established a starter you need to feed and maintain it with additional flour and water. All-purpose, refined wheat flour can be used. Most enthusiasts prefer stoneground wholegrain flours because they contain more of the microbes and enzymes needed to drive fermentation. They can, however, make a starter higher maintenance, requiring precise timing of feeding. Many opt for a more forgiving rye flour-based starter, and some use flour blends.
The lactic acids in sourdough neutralise phytates in flour that when consumed in large amounts can prevent the body absorbing minerals such as iron, calcium, magnesium and zinc in bread. They also slow the release of glucose into the bloodstream, lowering the bread’s glycemic index and preventing insulin spikes. The lactic acids also make gluten more digestible, and reduce the chances of gluten intolerance. A study published in December by Prof Marco Gobbetti, of the Free University of Bozen-Bolzano, in Italy, found sourdough to be more digestible than bread made with baker’s yeast. Sourdough fermented for longer periods made healthy individuals feel more full more quickly, and those who ate sourdough had higher amino acid concentrations in their blood.
The transformation of dough into a light and airy loaf is, after all, chemistry in action, with a good side of physics. The complex relationships between the yeasts and bacteria that power starter fermentation are the domain of the microbiologist. Whether you’re a beginner left holding bricks that taste of dough, or an accomplished amateur looking to further up your game, perhaps what you need is a refresher in the science of sourdough.