In a room with refrigerators in Belgium live more than 110 glasses of flour, water and magic.
At least you could sometimes think of sourdough starters, of bacteria and yeast cultures that bakers mix into doughs Instead of commercial yeast, a bread of delicious complexity is produced, which, depending on the recipe, has a pungent acidity or a firm creaminess.
As an appetizer, a welcoming slurry of flour and water is left on a counter and waited for microbes to settle on it, turning it bubbly and sour. But most bakers do not have DNA sequencers on hand to see exactly what's in their entrees, which often look, smell and taste differently. And where do the microbes come from? The air? The flour? The own microbiome of the baker?
Even if a starter replenished with flour and water, passed from person to person over a hundred years, is in the end really the same as it was at the beginning, it is an open question. [1
Fortunately, biologists and bakers are delving into the secrets of sourdough. To get a glimpse of a very interesting experiment, Cynthia Graber and Nicola Twilley, the team behind Gastropod, a podcast on food culture and science, went to Belgium with Belgium's two sour wine library Karl de Smedt with two microbial ecologists. (The resulting gastropod episode can be listened to here.)
The library was housed in a room at a company called Puratos, where de Smedt is head of the Bread Taste Center. Traditional chickpea biscuits contacted de Smedt and asked him if he liked helping to document and preserve his appetizer, Twilley says. The bakers were interested in switching from traditional starter sourdough to commercial yeast. He hoped de Smedt would help prevent the starter's disappearance.
The library grew when de Smedt gathered other notable starters and fed them with just the flour they would have had at home to preserve their uniqueness of character.
When Twilley and Graber entered the library for the first time, de Smedt counted down "Three … two … one …" and opened the door. "It was honest like a treasury in a museum," Twilley said. Behind the glass fronts of the refrigerators were point-lit glasses and a shimmering projection of leaves played over the ceiling.
The bakers were there to bake bread with their appetizers according to exactly the same recipe and to check whether the bread tasted different.
If the library reflects the attempt to collect and store unusual appetizers, the experiment helped Puratos and de Smedt Coordinating was an effort to understand how they came this way. In Belgium, together with de Smedt, who is also communication and training manager at Puratos, and the podcasters, there were 12 bakers from all over the world. The bakers were there because Anne Madden and Rob Dunn, microbial ecologists at North Carolina State University, had all sent them the same flour with the same instructions for making a sourdough starter.
They had brought their carefully prepared starters. Scientists were able to take samples to determine which microbes were present, whether they differed from starter to starter, and whether the microbes were also present in the hands of the bakers and in the original flour. The bakers were there to bake bread with their appetizers according to exactly the same recipe and to check if the bread tastes different.
The results of the Belgian experiment are currently being reviewed before publication. But Madden has recently shared some details about what they found. First, the starters were not all the same, although they were made in the same way with the same ingredients.
More than 350 strains of microorganisms were distributed over the starters, and most of the starters had yeasts from the genus Saccharomyces which also includes the baker's yeast. However, it was dominated by very different yeasts, the genera Naumovozyma and Kazakhstan . Another recent research group called the Global Sourdough Project, to study the effects of geography on the composition of different starters, notes that these yeasts are a distinctive feature of Australian starters.
Second, when they wiped the clean, washed hands of the bakers and cultivated the resulting microbes, the researchers found that the baker's hand microbiome was a little different from those of other people. They were more like the sourdough starter's microbial make-up, suggesting that the constant immersion of their hands in sour bread dough had affected the survival of the strongest on the hands of the bakers and had produced another group of tiny inhabitants. (Make no mistake – your body and your food play a role in natural selection, as do the larger habitats we've become used to.)
We pick the microbes that do what we want and Give us a good taste and give those who like us an evolutionary advantage.
Perhaps most interesting, however, is that almost all of the microbes found in the appetizers themselves were found either in the hands of the bakers or in the flour. Only 31 out of more than 350 were not, suggesting that the common belief that starter microbes are wild and floating in the air is less likely than that the microbes already in flour and baker's hands are the bread to bring up. Madden notes that it is difficult to determine the causality with the current data. It is not clear in which direction the microbes flow from the hands to the starter or in the opposite direction.
It is clear that sourdough starters and the bread made with them represent human manipulations of the development of microbes communities. We are directing the growth of certain members of these communities by raising or lowering the temperature of our dough, more or less frequently feeding starters and giving them different types of flour. We select the microbes that do what we want and that give us a good taste, and give those who like us an evolutionary advantage.
In all these point-lit glasses and in kitchens around the world, the selection is big at work, bringing us delicious bread.
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