What happens when starters share the same flour?

Sourdough Science

Sourdough has been part of human history for over 5,000 years, yet it continues to surprise us. At the Sourdough Institute, we’re always exploring new questions—and this time, we asked:If you feed different sourdough starters the same flour, will they become more alike, or retain their unique character?

To find out, we invited seven professional bakers and eight passionate hobbyists to take part in a bold experiment.

The Setup

Each baker received a bag of the same flour—a flour different from what they usually used to refresh their starters. Over ten days, they refreshed their own sourdough daily using only this flour.

After the tenth refresh, all participants gathered at the Puratos Sourdough Institute in Sankt Vith, Belgium. There, they baked loaves using identical ingredients, tools, and recipes. The only variable? The sourdough starter.

Tasting the Results

The breads were then sensory tested by the bakers themselves. Despite the shared flour and controlled conditions, the differences were unmistakable. Each loaf retained the distinct personality of its original starter—proof that sourdough is more than just flour and water. It’s alive with history, environment, and the hands that nurture it.

Bakers Become Their Bread

In a related study, Puratos teamed up with Rob Dunn and Anne Madden from North Carolina State University to explore another fascinating question:Do bakers influence their bread on a microbial level?

A Global Collaboration

Bakers from 16 countries were asked to create a sourdough starter using a common flour provided by Puratos. On July 4, 2018, they gathered at the Puratos Center to bake together.

Before baking, researchers swabbed the bakers’ hands and collected samples from their starters—both before and after feeding. These samples underwent DNA analysis to identify the fungi and bacteria present.

Surprising Discoveries

One of the most unexpected findings? Bakers’ hands were rich in Lactobacillus bacteria—the same beneficial microbes found in sourdough. While most people have some Lactobacillus on their skin, bakers had significantly more. It appears that through years of baking, the bakers had become their bread—literally.

Even more intriguing, the microbial profiles of the starters often matched those of the bakers’ hands. Some bakers had unique microbial signatures, and these were reflected in their starters. In other words, the microbes on a baker’s hands can shape the flavor and character of their sourdough.