Skip to content 
Discover the Sourdough Library in Belgium
Each September we celebrate Sourdough September. There’s a special place in Belgium, set up by Puratos that holds samples from bakeries across the world, the Sourdough Library.
The Sourdough Library
The Sourdough Library opened in 2013 currently it holds samples of around 150 different starters. The starters are stored and fed accordingly to the instructions provided by the original owner.
I was lucky enough to visit the Sourdough Library in 2016. The Sourdough Library is a beautiful room. Look up and you might believe you are in a forest with leafy trees above you. Along the walls are glass fronted cases, and inside them large jars each labelled with a number. Nothing else.
The Library is a non-profit initiative to collect sourdoughs from all over the world, to protect the sourdoughs’ diversity and to increase knowledge about them. It is the result of a long-term research program between Puratos and Professor Marco Gobbetti of the University of Bari.
In an initial study, where Gobbetti mapped and conserved sourdoughs from around Italy, the scientist and his team studied the micro-organisms of 19 different regional types of bread:
“We found a large diversity of mainly lactic acid bacteria among the sourdoughs,” Gob- betti explains. “We related such differences to the environmental parameters and the type of flour used […] such microbial diversity should be considered a sort of fingerprint for the uniqueness of each sourdough.”
Some of the sourdoughs had just a couple of types of lactic acid bacteria, others had many, contributing to each bread’s distinctive flavour. In fact, Scientists have discovered more than 700 different yeasts and more than 1500 lactic acid bacteria during this research.
Your sourdough starter reflects where it was made, the flour used and the maker itself. Research shows that 80% of sourdoughs share the same characteristics, but an amazing 20% differs.
Many of the sourdoughs studied formed the core of the Puratos collection in the Sourdough Library. The collection stood at more than 72 different samples in 2016 and is approaching 150 in 2024. Puratos sees no limit on the numbers of starters the library can accommodate. The library opened with samples from Italy, Greece, Hungary and the USA. Since then, samples from Italy, France, USA, Mexico, Australia, UK, Portugal, the Netherlands, Greece, Hungary and China have been added. Starters can always be provided to the original bakery should a disaster occur—actually, following a fire at one of the bakeries, the sample in the collection already enabled the bakery to continue as before.
Starter Storage and Maintenance
In the library, fresh sourdough samples are stored in special glass jars at a constant temperature of 4°C (29°F). Samples are also frozen and stored at -80°C in 4 different locations. The sourdoughs are refreshed to a set timetable, much longer than you or I might do with our sourdoughs, using the correct flour for that particular sample.
It is mainly the origin of the starter (original bakery environment and the flour used for starting the sourdough) that defines the bacteria in the sourdough. To preserve that bacteria, Puratos considers it essential to continue using the original baker’s flour.
Avoiding cross-contamination is also crucial. That’s why, when doing the refreshments, all the materials are cleaned and treated with alcohol before usage and in between each batch of sourdough.
Does the starter change in the library?
But does the sourdough stay the same? Every year, three sourdough samples from the library are randomly chosen to be analysed and compared with the initial results of the original sample collected. Until now, there have been no significant differences.
For each sourdough starter in the library, Puratos stores the following information:
- The starter’s backstory.
- The type of “back slapping” required. Back slapping is the addition of flour and water to refresh the sourdough.
- The type of flour used.
- Kneading time and at what temperature
- How long it should be left to prove and the baking temperature.
How can I get involved?
The Sourdough Library is not open to members of the public.
However, there is an online library of starters submitted from people all over the world – there are close to 3000 submissions. You can add yours too!
Add your sourdough at the Quest for Sourdough. You are quizzed on what your starter is called, how often you feed it, the temperature you feed it at and more. I’m about 80% through my submission, it does take time but it’s rather fun to complete!
Sourdough Library Sources
Take a virtual trip to the sourdough library.
Listen to the excellent Food Programme Podcast episode about the Sourdough Library including the fascinating link between one starter from Canada and another from Slovenia.
Much of this post originally appeared in my article in Issue 17 of the Bread Magazine when permission for use of photos was given.
1 thought on “Your Sourdough is unique”