Key takeaways:
- Sourdough fermentation activates enzymes in wheat that reshape fibre, not just microbes driving the process.
- Changes in arabinoxylan structure can affect dough performance, including viscosity, gas retention and bread quality.
- Fibre transformation may also influence flavour and digestibility, opening new considerations for formulation.
Sourdough is strongly associated with microbes – yeasts and lactic acid bacteria that drive fermentation, build flavour and give dough its lift. But that’s only part of what’s going on.
Because the flour isn’t just along for the ride – it’s changing as the process unfolds, and that has a knock-on effect for how dough behaves and how the final bread turns out.
New research from the Vrije Universiteit Brussel (VUB) takes a closer look at that side of things. Not the fermentation itself, but what’s happening to the wheat during it. The shifts aren’t dramatic and you wouldn’t spot them just by looking at the dough, but they’re there.
At the centre of it are arabinoxylans (AX), a group of dietary fibres found in wheat. Bakers will already be familiar with them, at least in practical terms. They influence water absorption, viscosity and structure, sometimes in helpful ways, sometimes less so. Water-extractable AX (WE-AX) tend to support dough systems or at least stay out of the way. Water-unextractable AX (WU-AX) are more often linked to heavier doughs and reduced quality.
That’s what Víctor González Alonso, a doctoral researcher at the VUB, set out to dig into, looking at how these fibres behave during sourdough fermentation.
“Wheat provides a large share of the calories and fibre consumed in Europe and arabinoxylans play an important part in this,” explains González Alonso. “They help determine the structure and quality of bread.”
Flour, not just microbes, is doing the work
What happens to those fibres once fermentation gets going hasn’t been especially clear. It’s generally been assumed that microbes were doing most of the altering. This study suggests it’s a bit more complicated than that.
The team followed sourdough fermentation across a range of flour types, including some enriched with additional arabinoxylans. Alongside the usual microbial tracking, they mapped the chemical changes in the dough using DNA sequencing and metabolite analysis.
On the microbial side, things behaved much as expected. Sourdoughs settled into stable ecosystems, with yeasts and lactic acid bacteria finding a balance and holding it. Increasing the fibre content didn’t really disturb that.
“We observed that sourdoughs develop into stable microbial ecosystems, with lactic acid bacteria and yeasts in a complex balance,” adds González Alonso. “A higher fibre content barely altered this process, although we clearly demonstrated that sourdough fermentation converts part of the WE-AX into WU-AX.”
Where things start to shift is elsewhere. As the dough acidifies – which it naturally does during sourdough fermentation – enzymes already present in the wheat begin to activate. These aren’t introduced by the microbes; they’re part of the flour itself. Under those acidic conditions, they start breaking down larger arabinoxylan molecules into smaller fragments. In the process, some of the more soluble WE-AX move into the less soluble WU-AX form.
This ties in with wider findings from González Alonso’s doctoral work, which point to wheat’s own enzymes – activated by acidity – as a key driver of these changes.
It’s not the kind of change you’d notice straight away, but it feeds through into how the dough performs. Viscosity, gas retention and structure can all shift depending on how those fibres evolve over time.
There’s also a balance to strike. Too much breakdown of these fibres can start to work against bakers, with earlier research suggesting excessive solubilisation may reduce bread volume.
So rather than fermentation simply acting on flour, the flour itself is being reworked as it goes.
Flavour, texture and potentially nutrition shift
The microbial role is still there, just not in quite the same way it’s often described.
The study linked specific strains to particular flavour outcomes. Lactococcus lactis was associated with buttery notes, while Limosilactobacillus fermentum produced sugar alcohols that can bring a mild sweetness. These effects aren’t universal – they depend on which microbes are present and the substrates available to them.
At the same time, the breakdown of fibre into smaller fragments raises questions around digestibility. Smaller components tend to be more soluble and may behave differently in the gut. The researchers are careful not to overstate this, but it does line up with the direction of travel across the category.
There’s already demand for breads that offer something more – higher fibre, easier digestion, a sense that the product is doing a bit more work. Sourdough is already part of that conversation; this helps explain why it might be.
The team pushed things further with a pilot baking trial, using flour enriched with arabinoxylans. The resulting loaves delivered higher fibre content, but that wasn’t the only shift. The flavour profile widened, too, suggesting the fibre changes and flavour development are more closely linked than they might first appear.
For millers and bakers, it adds another layer to consider. Flour doesn’t stay fixed once fermentation starts, and small shifts in fibre composition can carry through into processing and, ultimately, into the finished loaf.
“Sourdough remains a fascinating interplay of biology and craftsmanship,” says González Alonso. “And our research shows that sourdough fermentation influences wheat fibres to a greater extent than previously thought.”
Looked at that way, sourdough is less of a fixed method and more of a moving system – flour, enzymes and microbes all interacting, with fibre playing a bigger role than it’s usually given credit for.
Flour origin moves up the agenda
As new research highlights how important flour is during fermentation, attention is also turning to how it’s grown in the first place.
Matthews Cotswold Flour, one of the UK’s longest-running independent mills, has been working with local farmers since 2019 to develop regenerative supply chains. The company aims to transition fully to regenerative grain by 2030.
“We have long advocated for regenerative farming practices, which prioritise soil health, biodiversity and carbon capture,” says MD Bertie Matthews. “Through our Cotswold Grain Partnership, we work closely with farmers to ensure they adopt practices that protect the environment while producing high-quality grain.”
It has also expanded its regenerative range with five new flours for trade customers, all milled from wheat grown using these farming practices. Matthews adds that the focus is not just environmental, but also functional. “We are helping farmers grow grains that bring life back to the soil and flavour back to the loaf.”
The new range includes plain, self-raising, bread, wholemeal and cake flours, covering core bakery applications, available in 16kg and 1.5kg formats.
Study:
Vrije Universiteit Brussel (VUB). Scientists discover what really happens during sourdough fermentation. ScienceDaily, 16 March 2026.
