Does Sourdough Have Fructans? Understanding the Fermentation Process

October 15, 2025 •

4 min read

Scientific studies show that the long, slow fermentation process used in traditional sourdough baking can dramatically reduce the levels of fructans in bread. This process provides a nuanced answer to the question, does sourdough have fructans?, suggesting it can be a more digestible option for many individuals with sensitivities.

Quick Summary

The fermentation process of traditional sourdough significantly reduces fructan content, a type of FODMAP, by allowing the yeast and lactic acid bacteria to break down carbohydrates in the flour. The lower fructan level makes it more tolerable for those with sensitivities, particularly when made with refined wheat or spelt flour using long fermentation methods.

Key Points

Fructan Reduction: Traditional sourdough fermentation, a slow process involving lactic acid bacteria and wild yeast, significantly breaks down the fructans in flour.
Flour Choice Matters: Sourdough made with refined white wheat or spelt flour is typically lower in fructans, as these are concentrated in the bran and germ.
Long Fermentation is Key: A prolonged proving time of 12 hours or more is essential for maximizing the reduction of fructans and other FODMAPs.
Check Commercial Products: Not all store-bought sourdough is traditionally made. Check for ingredients like a live sourdough culture and confirm a long fermentation process.
Consider Mannitol: While fructans are reduced, some whole grain and rye sourdoughs may see an increase in other FODMAPs like mannitol, which can still cause digestive issues.
IBS Friendly Option: For many with IBS or fructan intolerance, authentic sourdough is a well-tolerated alternative to regular bread due to its reduced FODMAP content.

Fructans and the Fermentation Breakthrough

Fructans are a type of fermentable carbohydrate known as a FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols). These short-chain carbohydrates are poorly absorbed in the small intestine and can cause digestive distress, including bloating, gas, and abdominal pain, for individuals with conditions like Irritable Bowel Syndrome (IBS). While regular wheat flour is high in fructans, traditional sourdough production offers a solution through its unique fermentation process.

The Science of Sourdough Fermentation

Traditional sourdough bread is made using a 'starter,' a culture of wild yeasts and beneficial lactic acid bacteria (LAB), instead of commercial baker's yeast. This symbiotic community of microorganisms is the key to reducing the fructan content. During the long, slow fermentation (or proving) of the dough, these microbes become active and feed on the carbohydrates present in the flour.

Lactic Acid Bacteria (LAB): The LAB produce enzymes, including fructanases, which specifically target and break down the fructan chains into simpler, more digestible sugars.
Wild Yeasts: The wild yeasts in the starter also contribute to the breakdown of carbohydrates and aid in leavening the dough.
Extended Proving Time: The prolonged fermentation period, often lasting 12 hours or more, provides ample time for the microbes to consume and break down a significant portion of the fructans in the flour.

Studies have shown that this process can reduce the fructan content of wheat sourdough by up to 75% compared to regular yeast-leavened bread. The final fructan content depends on several factors, including the type of flour and the length of the fermentation.

Factors Influencing Fructan Levels in Sourdough

To ensure a low-fructan sourdough, several key aspects of the baking process must be considered. These include the type of flour used, the fermentation time, and the authenticity of the sourdough method.

Flour Type: The choice of flour is critical. Spelt flour, an ancient wheat variety, is naturally lower in fructans than modern wheat, making it an excellent base for a low-FODMAP sourdough. Refined wheat flour also produces lower-fructan sourdough than wholemeal varieties because fructans are concentrated in the bran and germ, which are removed during refining. Rye and whole wheat sourdoughs, though fermented, can still contain high levels of fructans and other FODMAPs like mannitol, potentially exceeding low-FODMAP thresholds.
Fermentation Time: A long, cold fermentation of at least 12 hours is essential for maximizing fructan reduction. Shorter fermentation times, as often used in commercial bakeries, may not allow enough time for the microbes to break down the carbohydrates adequately.
Authenticity: Not all bread labeled 'sourdough' is the same. Some commercial products are 'sourdough-style,' using baker's yeast and sour flavorings like vinegar, which do not offer the same digestive benefits. True sourdough relies on a live starter culture.

Sourdough for a Low-FODMAP Diet

For individuals following a low-FODMAP diet, incorporating properly made sourdough bread can be beneficial. Reputable organizations like Monash University, a leading authority on the low-FODMAP diet, have tested and certified certain sourdough breads as low-FODMAP.

Here are some tips for finding or making low-fructan sourdough:

Choose the right flour: Opt for white wheat or spelt sourdough bread. These flours typically result in a lower fructan product after traditional fermentation.
Verify the process: Look for bakeries that use a long, slow fermentation process, and ask about their methods. Avoid products that list vinegar or high-FODMAP sweeteners like honey.
Monitor serving size: Even with low-fructan sourdough, portion control is important on a low-FODMAP diet. Monash University provides serving size recommendations for certified breads.
Consider a certified product: Look for products with the official Monash University Low FODMAP Certified™ logo.
Bake your own: Making your own sourdough allows you complete control over the flour and fermentation time, ensuring the lowest possible fructan content.

Sourdough vs. Regular Bread: A Comparison


Feature	Traditional Sourdough Bread	Regular Yeast-Leavened Bread
Leavening Agent	Wild yeasts and lactic acid bacteria from a starter culture.	Commercial baker's yeast.
Fermentation Time	Typically long, slow fermentation (12+ hours).	Short fermentation (1–2 hours).
Fructan Content	Significantly reduced compared to flour.	High fructan content from flour remains largely intact.
Main Carbohydrate Breakdown	Microbes break down complex carbohydrates, including fructans, into simpler sugars.	Little to no breakdown of fructans, as commercial yeast is less effective.
Digestibility	Often more digestible for those with fructan sensitivity.	Can cause digestive issues for sensitive individuals due to high fructan load.
Flavor	Tangy, complex flavor profile from organic acids.	Milder, more uniform flavor.

Conclusion: The Digestive Advantage of Sourdough

The answer to the question, does sourdough have fructans?, is that while the raw flour certainly contains them, the traditional fermentation process dramatically reduces their quantity. This makes traditionally prepared sourdough bread, especially those made with white wheat or spelt flour, a much more digestible option for many people with fructan intolerance or IBS. The key lies in understanding the process and choosing authentic, slowly-fermented products. For those with sensitivities, the microbial work done by the starter culture is a game-changer for enjoying bread without the digestive consequences.

To learn more about FODMAPs and certified products, visit the Monash University Low FODMAP Diet Blog.

Frequently Asked Questions

Yes, traditionally made sourdough bread from refined wheat or spelt flour is considered low-FODMAP at specific serving sizes, as the long fermentation process significantly reduces the fructan content.

No. The fructan content depends on the flour type and the fermentation time. Commercially produced 'sourdough-style' breads with short fermentation and added yeast may still be high in fructans.

The lactic acid bacteria and wild yeast in the sourdough starter produce enzymes, like fructanase, that break down the complex fructan carbohydrates into simpler, more digestible forms during the long fermentation period.

Many people with IBS find that they tolerate traditionally prepared sourdough bread better than regular bread due to its lower fructan content. It's recommended to start with a small serving and monitor your symptoms.

Wholemeal and rye flours are higher in fructans and other FODMAPs. While fermentation reduces fructans, some studies show it can increase other FODMAPs like mannitol, meaning they might not meet low-FODMAP criteria for sensitive individuals.

Authentic sourdough uses a long fermentation with a live starter culture. Commercial 'sourdough' may use baker's yeast and a shorter process, or even flavorings, without the same level of fructan reduction.

Look for products that are certified by a reputable organization like Monash University. Alternatively, seek out smaller, local bakeries that use traditional long fermentation methods, or consider baking your own.