Sinking Your Teeth into Sourdough: The Science Behind Its Health Benefits
By Lauren Chan, PhD, RD, C2ST Intern, University of ChicagoIn the last six months, I became the proud owner of a sourdough starter gifted to me over the winter holidays. While I did not anticipate going on a. . .
, PhD, RD, C2ST Intern, University of ChicagoIn the last six months, I became the proud owner of a sourdough starter gifted to me over the winter holidays. While I did not anticipate going on a “sourdough journey”, it has been fun to not only learn how to make sourdough bread, but also the science and health benefits of sourdough!Sourdough is considered one of theoldest formsof leavened bread, tracing back to ancient Egypt. Leavened bread is bread that rises before baking. This can be done usingyeast, or in the case of sourdough, using asourdough starter. If you’ve been on “sourdoughtok” or other baking social media, you may know sourdough starters as jars of goop that bakers “feed” and use to make bread. What sourdough starters really are is a combination of flour and water that has fermented over a few days to weeks. Naturally occurring yeasts and lactic acid bacteria (LAB) found in the flour, water, and environment are what drive thefermentation process. Sourdough starter is sort of likeperpetual stew, where you keep adding more flour and water to constantly replenish it. This process makes the starter a stable culture, which can be used regularly to make sourdough products. A basic loaf ofsourdough breadis pretty simple, made of starter, flour, water, and salt. By mixing the ingredients together and doingstretch and foldsto create structure, the loaf is then ready to ferment. Sourdough makers call itbulk fermentation, which can take upwards of 8+ hours depending on conditions like kitchen temperature. Luckily for bakers, the dough does most of the work in this step. During fermentation, the yeasts and LAB from the sourdough starter will begin “eating” the carbohydrates found in the flour, creating air pockets and organic acids to make a bubbly, flavorful dough. Fermentation is the start of a great texture and flavor for the sourdough, but it also leads to a variety of nutritional benefits. Sourdough Supports Gut HealthSourdough contains“postbiotics”, or bioactive products that are beneficial to the body. Postbiotics are made during fermentation when the bacteria in sourdough convert macronutrients (like carbohydrates) into new compounds. One type of postbiotic made through the sourdough fermentation process isshort chain fatty acids (SCFA). Acetate, propionate, and butyrate are some of the SCFA found in sourdough. SCFA are also produced by the cells of the intestines, and eating sourdough canincrease SCFA production. The dual sources of SCFA support the many important roles these postbiotics play. Thesebenefitsinclude providing energy for colon cells, regulating metabolism, and supporting intestinal cell health. SCFA are also associated with reduced risk of inflammatory diseases and can help the body absorb minerals. Given the significantly higher levels of SCFA in sourdough compared to other types of bread, eating sourdough may be a better choice for gut and overall health. Fermentation Changes Nutrient AvailabilitySourdough bread, compared to yeast bread, has better nutrient availability. For example,zincis absorbed about25% more effectivelyfrom sourdough than from other bread. This is because fermentation can help break downanti-nutritional factors(ANF). ANF are components of food that can interfere with nutrients, making them harder to absorb. One example is phytic acid. Phytic acid occurs naturally in flour, so of course, it is present in bread. Phytic acid binds to minerals like calcium, magnesium, iron, and zinc, making it hard for the body to absorb them. Thankfully, the acidic environment, yeast, and LAB within sourdough can create the enzyme phytase, which breaks down phytic acid so the nutrients can beabsorbed more easily. Other food components are broken down by sourdough fermentation, includingfermentable oligo-, di-, and monosaccharides and polyols such as sorbitol and mannitol (FODMAPs). For some people with GI disorders like irritable bowel syndrome, FODMAPs can cause uncomfortable gastrointestinal symptoms. Thereduced FODMAPs contentin sourdough may make it a better option for people sensitive to them. Sourdough and Blood Sugar LevelsFor people who have diabetes or impaired glucose tolerance, it can be helpful to eat foods with a lowerglycemic index. Sourdough fits this bill, causing asmaller rise in blood sugarcompared to other breads. Once again, fermentation is the key, with the lower pH and LAB content changing the structure of the carbohydrates found in the dough. This structural change turns the carbohydrates into fiber. More specifically, they becomeresistant starches, meaning they are resistant to digestion and also slow the digestion of other carbohydrates. The combination of increasedfiber and slower digestionhelps to reduce and delay the absorption of carbohydrates and blood sugar spikes from sourdough. Research supports this too, withone studyfinding that for people with impaired glucose tolerance, sourdough causes a significantly smaller rise in blood sugar compared to regular bread. An Inside Look at Making SourdoughBefore baking, I will feed my starter (so I have more for next time) and let it sit on the counter for a few hours to “bloom” or start fermenting. See in the photos here how a freshly fed starter looks a little thicker, just how flour and water mixed together look. After blooming, the starter looks more liquidy and has air bubbles. Images 1-2. Left: Freshly fed sourdough starter, Right: “Bloomed” sourdough starter after a few hours at room temperature. As I mentioned earlier, sourdough bread starts with four primary ingredients: flour, water, salt, and sourdough starter. While there are many different techniques for making sourdough bread, the easiest approach is to mix everything together all at once to make a dough. Image 3. The “shaggy” looking start to a sourdough bread loaf. Once mixed together, I start into the stretch and fold process. This part of sourdough takes about two hours and is heavily reliant on my ability to set timers! Right after mixing, I let the dough rest for 30 minutes before doing my first round of stretch and folds. I do a total of four sets of stretching and folding, each with 30 minutes in between. The actual stretching and folding can happen in a few different ways, but I like to do a four-side approach where I pull up on the dough and fold it inward, turn the bowl 90 degrees and do it again for each of the four sides. Images 4-6 The stretch and fold process using a four-side approach. So far, the dough does not have much volume and is pretty stretchy. And now, we bulk ferment! One common complaint about sourdough is that it is a bit of a long process, but as we discussed earlier, the slow fermentation of sourdough is what gives it so many health benefits. During bulk fermentation, the dough will sit covered at room temperature for a few hours, with many of my fermentation times taking upwards of 12+ hours during the colder winter months (chilly weather makes fermentation slower than warmer weather). Image 7: The dough after the bulk fermentation process. See how much volume it gained compared to right after the stretch and folds! There are tons of big and little air bubbles in there, and if you were to poke the dough, it would spring back. After bulk fermentation, our blob of dough needs to start looking like a loaf of bread. This step is called shaping, where you use your hands or sometimes a bench scraper to push and pull the dough into a loaf shape and create a nice smooth surface on top. Images 8-10: Left: Dough right after bulk fermentation, not yet shaped. Middle: The shaping process, creating a smoother surface and making the dough a loaf shape. Right: The shaped loaf of bread. The shaped bread will take a little break in the fridge after shaping (I know, sourdough takes a while!) While the loaf hangs out in the fridge, it will start to develop more sourness and create a more flavorful loaf. Some people prefer a less sour bread and may not leave it in the fridge for very long, but others may leave a loaf in the fridge for 24+ hours to make it more tangy. Image 11: Shaped loaf of sourdough, ready for the fridge. When I’m ready to bake, I will preheat the oven and the dutch oven pan I will be baking my bread in. Once everything is preheated, I will pull the loaf out of the fridge and do some scores on the top with alame. Scores are important because the bread will rise while baking, and the pre-made scores help the loaf expand where you want it to. Without scores, the bread will expand and rupture somewhere else to expand as it needs. Then it bakes! After baking, I let the bread cool down before slicing and enjoying it. Images 12-14: Left: Scored bread, ready to bake. Middle: Bread in the middle of baking. Right: Finished sourdough bread. My sourdough journey has been such an interesting experience, both learning how to make sourdough and discovering how sourdough impacts health. I have also become very popular with friends and family by bringing sourdough bread or sharing sourdough starter at gatherings. Given all the positive benefits of sourdough, from gut health to blood sugar levels, I hope you will consider giving it a try!