top of page
  • Madeline Topf

Sourdough bread more "home-made" than homemade

In my favorite podcast, “Girls Gotta Eat,” they joke about the many stages of quarantine. The first stage was that push-up challenge. Then it was banana bread, crafts/puzzles, reconnecting with people you haven’t talked to in three years, and most notable, baking sourdough bread. I can’t say I didn’t partake in any of these… I definitely made banana bread and my apartment is decorated with misshapen macramé wall hangings. As for sourdough bread, well, the closest I got was the no-knead, barely-stir bread from the New York Times.

As a microbiologist, though, I work with many people who love having side fermentation projects. Kombucha, sauerkraut, yogurt, and, of course, sourdough. Sourdough is bread with a distinct “sour” taste that comes from the organic microbial cultures added to the bread. Its “starter culture” is easily made, maintained and distributed between friends. The culture consists of a community of bacteria and yeasts. This community can ferment the carbohydrates in the bread’s flour and produce CO2 which makes the bread rise. Normally, you would add baker’s yeast to make bread, which is just a more processed and “domesticated” yeast without added bacteria. The different enzymes, acids, and metabolites affect the bread’s flavor and texture, enabling sourdough enthusiasts and tech people to spend lots of time and energy optimizing their bread and telling everyone they know about it.

Does sourdough bread have terroir?

Although sourdough has been around for thousands of years, we don’t really know what microbes are that make up the starter. A paper by Elizabeth Landis and colleagues out of the Max Plank Institute (aptly published in 2021) described the microbial community of 500 sourdough starters from across the globe. They used DNA sequencing to identify what species the bacteria and yeasts were in the samples.

Interestingly, they found many of the communities dominated by a single yeast or bacterial species. Each community generally consisted of one yeast species and three Lactobacillus or acetic acid- producing bacteria. This acetic acid is the acid that gives sourdough its distinctive tang, and what separates it from other types of bread.

According to, to make a sourdough starter, all you have to do is mix 2:1 flour and water and let it sit on the kitchen counter. After a day or so, it should start bubbling. The bubbling means that bacteria and yeasts have started fermenting the carbohydrates in the flour and producing gas. It also signals it’s time to “feed” it. Feeding means you add more flour and water until it starts bubbling again. Basically, the microbes need more food to keep living and growing. If you didn’t feed it, they’d all die.

What amazes me is these bacteria and yeasts are with us all the time, just floating around! All they have to do is land in the right spot to live, thrive, and maybe make us delicious food. The authors of the paper wondered if the bacteria present in each starter were different based on where geographically they collected the sample.

Although they didn’t find any particular microbial composition associated with geographic area, they did find certain species enriched in regions of the US. So, the Midwestern sourdough starters had particular bacteria not found in the East Coast samples, and vice versa. Could that mean that sourdough has terroir?

Sourdough may have hit its peak while we’ve all been bored and trapped at home. In a way though, it illuminates a piece of home we’ve never thought about. It develops it and gives us back something. It creates food from air, the same air we’ve been inhabiting the past year. Sourdough creates food from parts of us.

bottom of page