What is sourdough? Adapted from Optimum Nutrition Autumn 2017 Feature Full of flavour and character, we take a closer look at this popular bread A properly fermented sourdough loaf demands appreciation – not only because it tastes so good, but because it requires time, patience and care to get right; plus a little help from some invisible friends. What is sourdough? The big difference between sourdough and the 'normal' bread you buy is the source of the yeast. Most loaves use cultivated yeast that comes in a package and has been dried, preserved and formed into a powder. You add flour, water, sugar and salt to the yeast to make a loaf of bread. The water re-activates the yeast fungi, which feeds on the sugar and starch to make the bread rise. Sourdough bread deals with yeast in a completely different way. The fungi are actually kept alive constantly in a liquid medium called a starter (also called a ‘mother’, ‘chief’ or ‘leaven’) and an ecosystem of wild yeast and lactic acid bacteria that are naturally present in flour and the environment. These fermenting bugs give sourdough its distinctive flavour and character, through the production of compounds such as carbon dioxide, alcohol, and organic acids as they feast off the flour. How to make sourdough To create a starter, you need to mix some flour and water into a paste, and then wait for the microbes to do their thing. There are no special ingredients required, just a little patience and the right conditions. Each day the starter needs to be fed with more flour and water. When the starter is a bubbly, frothy mass, it’s ready to use to make tangy loaves of sourdough bread that are full of holes and flavour. A portion of the starter can be kept back and refreshed for the next bake; in fact, starters can be maintained indefinitely. Vanessa Kimbell, a baker and chef who runs The Sourdough School near Northamptonshire, says that humans have been fermenting bread this way for thousands of years. “The first written evidence is in the Egyptian tombs, about three and a half thousand years ago, but there is evidence of fermenting grains from over 10,000 years ago from archaeological discoveries.” Kimbell started working in her village’s bakery in the Dordogne, south-west France, at the age of 11, with great bread at “the heart of every meal” she ate while growing up. Despite sourdough sounding difficult and time-consuming to make, she assures us it’s not. “It is a process that takes about 20 minutes of total work over 36 hours. Like with any new skill it takes time to really make beautifully crafted bread, but learning is half the fun.” Sourdough vs Sourfaux In contrast to the live sourdough starters that teem with billions of wild yeasts and bacteria, a fast-acting commercial Baker’s yeast that is used in today’s standard factory loaves comprises a single species of Saccharomyces cerevisiae, which was bred for speedy growth. That’s not to say supermarkets don’t stock sourdough breads - they do; but not all so-called sourdoughs are made equal. According to the Real Bread Campaign, part of the charity Sustain (the alliance for better food and farming), some of them should not be labelled as sourdough at all. Referring to some mass-marketed sourdoughs as “sourfaux”, the Real Bread Campaign’s aim is for a legal definition for the name, so that shoppers know exactly what they’re buying. What are the benefits of sourdough? Flavour aside, many sourdough fans say that there are real benefits to swapping your standard loaf for a sourdough bake. “Sourdough,” says Kimbell, “when made properly and with some wholegrain flour, will give you more nutrients - both vitamins and minerals - than a yeasted bread, and will also help lower blood sugar response, provide higher levels of resistant starch, and keep you fuller for longer.” She also says that the breads may contain higher levels of bioactive peptides, which have been associated with a number of health benefits. “We are not talking about a total health revolution the first time you have a slice of toast, but over time small daily decisions add up… and it is also delicious.” The research, however, has produced mixed results. A 2008 study found that participants with impaired glucose tolerance produced a significantly lower glucose and insulin response when given sourdough bread, compared to those given ordinary bread leavened with Baker’s yeast. The authors concluded: “This effect is likely due to the lactic acid produced during dough leavening as well as the reduced availability of simple carbohydrates.” A more recent study, however, suggested that only some people will experience these blood sugar benefits – with it dependant on the individual’s gut bacteria. No significant difference was found in any of the health parameters studied, including glycaemic control, between traditionally-made sourdough-leavened whole-grain bread and industrially-made white bread when eaten for one-week each. And looking at individual responses, it was found that some people responded better to sourdough bread, while others responded better to white bread. The response could also be predicted by a person’s microbiome (the types of bacteria in the gut). Another benefit commonly ascribed to sourdough is that it is easier to digest. There is even a suggestion that it might be suitable for some people who consider themselves gluten- sensitive. (It should not be eaten by anyone with coeliac disease.) One of the advantages of the long sourdough fermentation is that it allows the bacteria to break down the gluten, but this does not mean it is gluten-free (unless, of course, it is made with a gluten-free flour). “We teach our students how they can ferment bread to get the maximum gluten degradation in wheat, which does contain gluten, but you cannot call this gluten-free,” says Kimbell. If you enjoyed this article, why not subscribe to our free digital Optimum Nutrition magazine?