The Science of Sourdough

There are millions of kinds of bacteria and fungi on Earth. We have found several thousand species in human belly buttons alone. Yet if you mix flour and water, the community of organisms that colonize the resulting concoction is almost always composed of a small handful of organisms that are able to leaven bread, yielding a sourdough starter. How this happens is one of civilizations great mysteries, a mystery at the heart of the bread making (and, for that matter, traditional beer brewing). Yet, while bakers understand how to make starters, the underlying biology of the species in these starters remains mysterious. But not for long. We aim to understand the biology underlying the differences among starters and the changes (or lack of change) in starters through time.

Wild Sourdough
With the aim of making it easier for anyone in the world to engage in sourdough science and produce tasty bread, our new project is relatively simple. We want people to make sourdough starters at home under different conditions (different flours, indoors/outdoors) and in doing so to measure how fast their new starters rise and how they smell. In this effort, which represents a partnership with bakers, universities and museums around the world, we hope to see through many thousands of data points, the big patterns in the rise and stink of starters.

But we want to do more than science here, we want to build community. Our hope is that in making starters as part of a common project, that people can come together around food, science, heritage and flavor.

Sourdough for Science

The microbial communities in sourdough are easy to grow and study, making them a great study system for home experiments and science education. By participating in a real science project, students and non-students alike can help us solve the mysteries of bread. Your data will be compared with data from other participants, all over the world, who have completed the same experiment. Together we can use these data to learn how different flours affect microbial growth over time – and how those microbes affect the taste and texture of bread.

The Global Sourdough Project 

Over 500 Citizen Scientists from around the world contributed samples of their own sourdough starters for us to analyze. Twice that many answered an extensive questionnaire related to the origin and maintenance of their starter. We are using genetic techniques to determine which species are present in the starters and statistical approaches to compare the different communities. By doing this comparison we can begin to understand the factors that influence which community lives in one starter relative to another, why your starter is different from that of someone else.

The Belgian Experiment

It is entirely possible that when you make a starter that the particular Lactobacillus that you seed it with are your own symbionts. But how would we possibly know?  This is where The Belgian Experiment comes in. In July of 2018 we united bakers from around the world at the Puratos facility in Belgium. Before convening, each baker made a starter at home, which they brought with them. We then sampled the microbes in the resulting starters, as well as those on the bakers’ hands, before baking loaves of bread to sample.  For a given set of ingredients we can now start to tease apart how how important the person who made the starter, and their microbes, are to the microbes in a starter, as well as the chemistry and flavor of the bread.

The Discard

Not all of our experiments go as planned. While failed projects and plans are an inherent part of science, we sometimes tend to gloss over the mishaps when sharing our results outside of the lab.  So here is our ode to our experimental “discard”, the projects and pilot studies that, while they might have served a purpose at the time, have been chucked in the bin to leave resources for other projects to grow and flourish.

  • Sourdough Project 2.0  – We should have known better than to try to send international conference-goers home with bags of white flour. Turns out customs officers don’t approve.