This piece was written by one of our contributors; medical student with BSc in human nutrition and MSc in clinical and public health nutrition – Rebecca Fox.
With supermarkets running low on flour and other baking supplies, it seems like everyone is taking advantage of baking while in lockdown. While some are choosing to hone their skills in sweet treats, others (myself included) are trying out one of the biggest baking trends infiltrating everyone’s instagram feeds: sourdough bread.
But what is it?
Starting a few steps back, all types of bread – sourdough or otherwise – require yeast to rise. Yeast (generally speaking) are a type of single-celled microorganism that produce carbon dioxide (which you’ll see as bubbles) after they consume natural sugars present in the flour used to make the bread dough. These carbon dioxide bubbles become trapped in the dough as the bread rises. This leaves the bread with a light and fluffy texture after baking. However, there are many types of yeast – not all created equal. The type of yeast used in a bread recipe influences its texture and flavour. Most of the typical sandwich loaves you’ll see at the supermarket use baker’s yeast (Saccharomyces cerevisiae is the species of yeast, if we’re being technical). This also a common type of flour you’ll find in the shops. When using this type of yeast for baking, you simply add it to a bit of warm water and sugar (i.e. yeast food) to allow the yeast to grow and divide before adding it to your doughy melange.
On the other hand, sourdough bread uses a slightly different technique involving a “starter”. Starter is pretty self-explanatory; it causes the dough to rise. A starter is the mixture of water and flour that is left out – morning ‘till eve. This is the cool part: there are plenty of yeast and bacteria floating about in the air around us . These different strains of yeast and bacteria all contribute different texture and sour flavour to the bread. The “souring” effect on the dough occurs mainly due to the presence of lactic acid bacteria (LAB) present in the starter. These LAB’s produce organic acids (mainly lactic acid) which helps to make the dough slightly more acidic. This is where that sour flavour comes from. However, in addition to the altered texture and flavour components, these structural and chemical changes in the bread’s composition by bacteria and yeast may also have some health benefits.
FODMAP’s (fermentable oligosaccharides, monosaccharides, and polysaccharides) are types of sugars that are often difficult for some people to digest, and may cause symptoms of irritable bowel syndrome (IBS) such as bloating and gas . It turns out that some of the different strains of yeasts and bacteria found in sourdough break down some of these sugars while the bread is rising. This potentially makes it easier to digest for people with IBS .
In addition, sourdough is made with a probiotic culture (i.e. live bacteria and yeast). These probiotics don’t survive the baking process, however their benefits remain. The bread’s digestibility and texture is altered by probiotics during the rising process. These changes remain after the bread is baked, allowing it to be considered a “prebiotic”, helping feed the friendly bacteria in your gut .
So, is baked sourdough good for the gut? YES! While it does not contain probiotics, the gut friendly benefits come from the fact that they were there in the first place.
Blood sugar control
In addition to helping digestion, some of the properties of sourdough may be useful in helping control blood sugar. The glycemic index (GI) refers to how quickly your blood sugar spikes after eating. GI is higher for foods that have lots of refined sugars or that are low in things like fibre. Plain white bread is often used as the standard for indexing GI of other foods, as it has one of the highest GI’s . Sourdough, on the other hand, has a low GI as the bacteria and yeast present in the dough during rising appear to be able to alter the structure of certain types of fibre present in the bread- resulting in a slower digestion and a lower GI .
It’s important to mention though that other types of bread besides sourdough also have a lower GI than white bread, including whole wheat, whole grain, and rye breads.
Sourdough’s yeast and bacteria may also be helpful for increasing the availability of certain vitamins your body can absorb from the bread. In particular, some studies have shown that longer sourdough fermentations may be able to increase the bioavailability of folic acid and thiamin in wheat flour . Furthermore, wheat naturally contains a chemical called phytic acid . Phytic acid can limit your body from being able to absorb and use certain minerals such as calcium and iron . However, there are certain enzymes called phytases that can break down phytic acid, thus helping increase the availability of these minerals for absorption. These phytases are more active at lower pH’s though (i.e. higher acidity), and are therefore more active in sourdough bread due to the greater acidity produced from those lactic acid bacteria mentioned earlier. So, the composition of sourdough itself may be able to help reduce some of these phytates and improve availability of certain minerals.
One important point to note is that these studies were performed in North America, where flour is required to have folic acid, thiamin, riboflavin, niacin and iron added during fortification . Different countries have different regulations regarding flour fortification with vitamins and minerals. The UK for example mandates that only iron, thiamin, and niacin be re-added into white flour after milling as these nutrients are found predominantly in the bran portion of the wheat that is removed in the refining process . Thiamin is present naturally in wheat flour, while folic acid is not. Therefore, if you’re buying flour in the UK, these small increases in vitamin availability may not be relevant.
To summarise, sourdough differs from regular yeasted bread due to the types of natural yeast and bacteria used to help it rise. These microorganisms help change certain structural and chemical aspects of the bread dough that confer potential health benefits. However, starters will be slightly different based on where you are in the world as climates and environments alter the composition of bacteria and yeast available for a sourdough starter. So, as some of these health benefits are based on the types of bacteria and yeast present, they are not all encompassing and won’t necessarily have an impact on everyone’s dough.
On your marks, get set, bake!!
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