Who Lives in a Sourdough Starter and How Did They Get There?

Sourdough starters begin with a simple mixture of flour and water, which under the right conditions spawn microorganisms (bacteria) and wild yeast. Once established, and if regularly fed, these microscopic beings thrive without spoilage.

Microorganisms exist on all grains. When the grain is ground (flour) and added to water, those microorganisms wake up and start to proliferate. They do this by eating the starches in the grain and breaking them down into sugars, producing gas and enzymes. To stay alive, the microorganisms need food to eat, hence the requirement to feed the starter often.

Wild yeasts live in the air. To attract them to a new starter, often a piece of fruit is added to the flour and water mixture. Yeast likes a slightly more acidic pH and the fruit does a nice job of acidifying the mix, making it more hospitable for yeast. Food for the yeast is necessary too, and is provided by the sugars from the fruit initially and then by the microorganisms breaking down the grains/flour. Yeast also needs water to thrive. Since the sourdough starter is a mixture of flour and water, the yeast has the nourishing environment it needs. When some of the yeasts die, their proteins break down into amino acids that can be used as food by lactobacilli. The starter is a symbiotic system. The yeast and bacteria coexist well because they don’t compete for food.

Microorganisms Accentuate the Positive and Eliminate the Negative

Not only do those microorganisms and wild yeasts turn the single note of ordinary bread into an orchestra of flavors, using your sourdough starter to make bread also extends shelf life, enhances the bioavailability of nutrient-rich wheat, and tames the gluten that many find an irritant. Is sourdough bread considered a probiotic food? Many would say there is definitely life in your loaf.

THAT FLAVOR

Lots of bread lovers crave the tanginess of sourdough bread. This distinctive flavor comes mainly from the lactic acid and acetic acid in the starter. The balance of microbes informs the flavor of the brew. You can also adjust the flavor (see this page). Refined tasters may also be able to pick out the subtle flavors that come from different types of flours used to create and feed the starter.

When food enters your mouth, a multitude of signals are sent to the brain and the digestive system for evaluation. Not only does the taste help us decide what to eat, it also influences how efficiently we digest food. When food has a sour taste, our body gears up for better digestion. The sourness increases salivary secretions and stimulates the production of HCl (hydrochloric acid), which fuels the breakdown of food once it hits the stomach. In Ayurvedic medicine, the sour taste is thought to awaken the mind and coalesce scattered energy. Useful.

STAYING POWER

Commercially made non-sourdough breads are prone to spoilage, mainly due to the growth of molds. To make breads last, companies add fungal inhibitors such as ethanol or propionic acid to the dough to delay the growth of mold. Replacing oxygen with carbon dioxide during the packaging process also stops bread from deteriorating on the shelf. The natural alternative to lasting bread: sourdough.

The acids inherent in sourdough breads extend the shelf life. Acetic acid and the metabolites produced by the lactic acid and wild yeasts both work to inhibit the growth of mold.

Spoilage of bread is further delayed when the dough contains at least 15 percent sourdough starter. The recipes in this book use a long fermentation period, where starter plus flour and water mingle, essentially creating a super-big starter, easily over the 15 percent mark.

NUTRITIONAL BENEFITS

Sourdough bread is typically made from wheat, which, despite its current bad-boy profile, is a remarkable grain. Farming settlers in the United States chose wheat as the grain to grow for many reasons, perhaps most importantly because it has the ability to provide year-round sustenance. Whole wheat is not only plentiful in complex carbohydrates and a wide array of B vitamins, its mineral profile is impressive too. If the grain is left whole, the germ offers valuable vitamin E.

The high mineral content (especially calcium, potassium, magnesium, iron, zinc, and phosphorus) in whole grains and beans comes in tandem with phytic acid. The phytic acid forms insoluble complexes with the minerals, preventing them from being absorbed and available for humans. Sourdough to the rescue! Its acids activate an enzyme present in grains—phytase—that cleaves the complexes, allowing the minerals to be freed and absorbed at a much higher rate. Soaking and fermenting the flours kick-start this beneficial enzymatic activity.

Bread is often avoided by those affected by weight gain, diabetes, and metabolic syndrome because of its high glycemic index (GI), which, due to rapid digestion, can create a spike in blood sugar. Whole grain sourdough bread makes this issue null and void. Sourdough bacteria produce acetic, propionic, and lactic acid (organic acids) that, under the heat of baking, cause interactions that reduce starch availability, lowering glycemic responses when eaten. Emphasis on whole grain. Sourdough white bread doesn’t produce the same GI-lowering capabilities.

Studies extolling the health benefits of eating whole grains, like whole wheat, include evidence of lowering the prevalence of certain cancers, heart disease, diabetes, and weight issues. This may largely be due to the excellent fiber content of whole wheat.

PREBIOTICS

We know that fiber helps keep food moving through the intestines, but there is a much more impressive benefit to eating fiber-rich breads. Wheat, barley, and rye contain the fiber inulin and oligosaccharides, which turn out to be excellent sources of food for the good bacteria in the gut.

Many Americans consume a low amount of fiber in their diet. Fifteen grams daily is the average. Many microbiome experts recommend upwards of 30 grams per day for good gut health. A half cup of whole wheat flour brings 7.5 grams of fiber to the table.

When gut bacteria don’t get enough food (fiber) they will have limited proliferation. A large population of healthy bacteria promotes overall health. And without enough fiber to feed the microbes that are present, they may resort to eating the mucous in the gut, which can thin out the lining. A permeable gut lining is often associated with food allergies. The fiber inherent in whole grain sourdough breads provides impressive prebiotic benefits. The bread may offer probiotic assistance as well (see Are the Microorganisms Still Alive after Baking? on this page).

GLUTEN ADJUSTMENTS

Anecdotally, people with a sensitivity to products made from wheat claim that fermented sourdough breads are surprisingly tolerable. There are convincing reasons for this.

Wheat has two types of gluten-forming proteins: gliadins and glutenins. After water and mechanical energy (kneading) are added to wheat flour, these proteins combine to form functional gluten, which is what gives doughs their unique gas-holding and viscoelastic properties that create leavened breads. Gliadins contribute to the dough’s ability to extend and be stretched. Glutenins help develop structure and an elastic property that resists too much stretching. Together these two proteins resemble the elasticity of a rubber band—stretch and bounce-back.

Gliadins are considered the most problematic in triggering Celiac disease and are hence the most studied. A peptide (a small section of protein thirty-three amino acid units long) that is present in the gliadins is thought to be the most challenging. Sourdough provides first aid again, as the lactic acid bacteria (LAB) can modify the bits of gliadin protein in wheat flour, making it more tolerable.

This idea is supported in recent studies where gluten concentrations are found to be dramatically reduced (from 80,000 parts per million [ppm] to around 2,500 ppm) in fermented sourdough breads. The longer the dough ferments, the more the gluten is broken down. Through a process called hydrolysis, enzymes break down large, indigestible proteins into smaller amino acids. Though these breads may not be tolerable for sufferers of Celiac disease, it could be promising for those with non-Celiac gluten intolerance. People who consume sourdough-fermented products report less bloating and abdominal discomfort than when they eat breads solely leavened with commercial yeast.

The additional wheat gluten (a derivative product) laced into commercial breads is also seen as a possible cause of the gluten-sensitivity trend. And there’s a good deal of information pointing the finger at the pesticides used on wheat being more culpable than the gluten for causing gut-related issues. Compelling, as all pesticides are essentially antibiotics, which are nondiscriminant in killing both beneficial and harmful bacteria in our bodies.

Returning to the old ways of making fermented sourdough breads from organic whole wheat flours may result in a superior food for all of us, even the gluten sensitive.

Are the Microorganisms Still Alive after Baking?

A blog post titled “Top 10 Reasons to Eat Sourdough” went up over five years ago on my website, Cookus Interruptus, and it continues to generate comments. The conversation centers on whether sourdough breads can still be considered probiotic after baking. Most people assume the heat kills the microorganisms. Maybe not!

Sample comment: “One day, I took a piece of the crumb of one of my loaves that I baked at 230 degrees Celsius and placed it in a small bowl with very little water. I repeated the operation for a few more days and surprisingly got a new starter, which I also use to make breads because it tastes amazing.”

A 2015 study on the viability of probiotic bacteria in sourdough bread after baking provides the reason behind these seeming miracles. The researchers found that some bacteria do die during the baking process. But, the bacteria that do survive, after recovering from the stress of baking, begin to acclimate to the new environment of baked bread versus dough and start proliferating. The phoenix rises from the baked crumbs! In the study the bacterial amounts increased for a period of four days and then remained stable for three days after.

Mystery solved. There is life beyond the oven. And it is totally possible to create a new starter or a new loaf of bread with a piece of your last loaf.

A complete list of the references for the scientific information on sourdough can be found on this page.