Sourdough > sour coffee

6 minute read

“Man lives for science as well as bread”

William James

A couple of weeks ago, I put up a story on Instagram offering to ship a bit of dehydrated sourdough starter to anyone who wanted it. I thought it would be fun to send something through the mail like the quarantine letters sent a century ago, and a way to support the embattled U.S. Postal Service. I liked the idea of sending copies of my starter on horseback in seven different directions in case tragedy were to befall my own, backups stored on flash drives made of patience and grain rather than silicon.

I’ve been baking bread since 2014, I think—the quote above is inscribed in the copy of Ken Forkish’s Flour Water Salt Yeast that I was given for Christmas that year. At first, I was intimidated by the maintenance requirements of sourdough, so I leaned heavily on the poolish and biga recipes in the book, which, while incredibly delicious, require less dutiful attention and offer greater predictability for a novice baker.

That changed a year later, when I was living in Brooklyn, New York and, in an unforeseen turn of events, found myself with some combination of too little money, too much time, and little to do other than stay home and cook. (Who could have known how useful practicing with that set of circumstances would later become)

Slowly, I began experimenting with sourdough using Chad Robertson’s method from Tartine Bread, settling into a weekly ritual of mixing, folding, waiting and baking. My counters and floor, previously speckled brown with coffee dust, took on a whiter hue as King Arthur and his knights of the stoneground-table marched through my kitchen every Sunday.

I’ve baked sourdough nearly every week since.


A couple of loaves I baked from freshly-milled hard red and white wheats. IIRC this was a 92.5% hydration, 15% salt, 2.3% salt dough.
A couple of loaves I baked using my Star Alliance Gold starter from freshly-milled whole hard red and white wheats. If I remember correctly, this batch of dough was 92.5% hydration, 15% starter, and 2.3% salt.

Baking sourdough is the most practical form of black magic. When the yeast runs out, we summon it from the air—like a sort of conjurer, or witch. As the shelves sat bare in the face of COVID-19, my kitchen carried on, turning out loaf after loaf of bread using the starter I’d grown and kept for years like a starchy goldfish.

What we know about coffee—a product that typically undergoes fermentation as part of its production—can inform our understanding of sourdough. This is because, as Roseane Schwan writes in Cocoa and Coffee Fermentations, “fermentations of cocoa and coffee should not be seen as microbiologically unique processes but, instead, in the broader context of mixed microbial fermentations.” Specifically, fermentation of coffee involves “the activity of a wide range of microorganisms such as yeasts, lactic acid bacteria (LAB), acetic acid bacteria (AAB), spore-forming bacteria, and molds.” (Masoud et al. 2004; Schwan and Wheals 2004; Nielsen et al. 2007, 2013).

Sourdough, like coffee, undergoes a mixed microbial fermentation. And like in coffee, sourdough fermentation is largely driven by the metabolic activities of lactic acid bacteria and yeasts such as Saccharomyces Cerevisiae and Candida. Yeast and bacteria living on your hands, on the flour, and floating through the air take up residence in the slurry of flour and water, feeding on the sugars in the grain to multiply and convert that sugar into cellular energy—ATP. Byproducts of the fermentation, such as lactic or acetic acid, are the “sour” in  sourdough and responsible for its characteristic zing.

The microbes in a starter can take awhile to achieve a biomass and begin their metabolic production—an observation that frustrates many new quarantined sourdough enthusiasts, if social media is any indication. What you feed them, how often you feed them, the temperature they’re kept at, the concentration of available sugar and nutrients, their exposure to air, the freshness of the flour, and the starting population of microorganisms will determine the dominant microbes in your culture and their rate of reproduction and fermentation. 

Just like you can change the rate of fermentation and flavor of your coffee by fermenting underwater with cool water rather than fermenting pulped coffee dry and in the sun—or by fermenting in a closed container with an airlock or exposed to open air—you can change the fermentation of your starter and flavor of your bread by fermenting in the fridge rather than at room temperature, or by feeding it equal parts flour and water rather than feeding it more of one than the other.

Environment—particularly availability of nutrients, temperature, and acidity—will determine the strength, population, and metabolic characteristics of the microflora in your starter (or your coffee fermentation) by creating advantages for certain microbes over others. Many bakers take great care in the feeding schedules or diets of their starters to try to narrowly and with some precision produce a set of attributes they prefer for the bread resulting from the population of microbes selected.

Once you have established a resilient culture of microbes, you have created your starter—a mother, from which theoretically infinite starters could be generated and infinite loaves could be baked.

It’s the perpetual motion machine of carbohydrates.

While the generic species and genus of the microbes in your starter may be knowable, the specific genetic composition of a starter is regarded by bakers (without any real evidence) as unique. While native microbes have an advantage being adapted to a local environment will, over time, overtake the population of species from an inoculation, a sourdough culture should maintain its vigor as it’s kept relatively isolated from the environment and fed with regularity to maintain strength. For this reason, starters of a certain age or pedigree are prized, and many bakers seek out discard from established or successful starters from professional bakers to begin their own starter.

There may be some truth to that folk wisdom—at least, if we can extrapolate from coffee literature.

In a search for novel species of yeast to use in medical bioengineering, Aimée Dudley and her collaborators showed that by swabbing and culturing the microbes from green coffee from different origins, you could develop a sort of microbiological genetic fingerprint of a place of origin (I used the same culturing technique to investigate the effects of yeast inoculation in coffee fermentation on fade). 

Some might be tempted to call the evidence of a distinct genetic microbiome in coffee “terroir”—but in reality, it’s more illustrative of the nature of the coffee trade, the export of coffee cultivation from Ethiopia and Yemen across the world, and human migratory patterns:

Our results uncovered populations that, while defined by niche and geography, also bear signatures of admixture between major populations in events independent of the transport of the plants. Thus, human-associated fermentation and migration may have affected the distribution of yeast involved in the production of coffee.

Side note: I have some thoughts about the use of the word “terroir” in coffee that I’ll share another time

Like coffee—which originated in Ethiopia and then migrated around the world from Yemen and Indonesia to the New World through commerce, colonization and the labor of enslaved humans—wheat, one of the first crops to be domesticated and cultivated by humans, originated in the fertile crescent and Near East and later was planted, bred, and selected around the world, leading to various varieties and landraces traditional to certain regions. Wheat (and corn and rice) would grow to be the bedrock of civilization.

In other words—through bread, human society was made possible.


In the early days of the pandemic, when uncertainty was the only certainty and every time we had Wine With DeWine we had to rework our business model and rethink if we wanted to stay open, “essential business” or not—I’d check the COVID-19 tracking map from Johns Hopkins, watching the numbers tick up as the virus spread around the world.

Coffee and wheat migrated across the earth as humans migrated, colonized, and settled; Disease did, too.

When the world went into quarantine to flatten the curve and finally do something to control the pandemic, I watched on Instagram as friends and acquaintances tried their hands at sourdough—harnessing microbes for good, productive purposes to distract from and counteract the microbes spreading suffering in their communities.

Not all microbes are the enemy.

When my friend Meister messaged a tale of sourdough starter woe, I decided it was time I make a more productive map than the one I refreshed like a stock ticker during a quarterly earnings call. I wanted to send tiny shards of yeast and lactic acid bacteria clinging to dehydrated flour in forever-stamped envelopes around the country and watch their paths extend like spider legs across my screen.

So I queried my followers, asking who wanted a bit of my starter, dehydrated it, and shipped it through the postal service. And then—like the CDC—I tracked where I sent it.

While I’m at home, donning my mask like Billy the Kid—my future flights cancelled and hard-earned Star Alliance status benefits sitting unused—my starter traveled the world to stay at home with you.

That little piece of time and magic now lives in 11 different states and 4 time zones of the country, feeding dozens and helping save countless others by keeping people indoors to make bread. As time goes on, I hope the recipients of my starter grow their own version and share it with others (it is, after all, called a “culture”) and tell me where else it’s gone so I can add more little dots and spokes to my map.

Western civilization was built on bread: If we can’t break it together, the least we can do is share a bit of our starter.

Without further ado, here’s where my starter lives now:

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