Is Sourdough Bread Gluten-Free?

No, sourdough bread is not gluten-free. Sourdough made with wheat, rye or barley still contains gluten and is not safe for people with celiac disease. Fermentation breaks down some gluten, but nowhere near the under-20 parts per million the FDA requires for a gluten-free label. Only sourdough made entirely from gluten-free grains and a gluten-free starter is gluten-free.

The confusion is understandable. Sourdough has a reputation for being gentler on the gut, some people with gluten sensitivity say they tolerate it better, and you may have seen headlines about studies in which fermented wheat bread was safe for celiac patients. Those studies are real. They just did not use anything like the sourdough you buy or bake.

Why isn’t sourdough gluten-free?

Because it is made from gluten-containing flour. Gluten is a group of proteins found in wheat (including spelt, einkorn, emmer and Khorasan), rye and barley. Most sourdough is made from wheat flour, often with some rye, and is fed with the same flours.

During fermentation, the lactic acid bacteria and the flour’s own enzymes do break down some protein, including some gluten. Beyond Celiac acknowledges that fermentation decreases the amount of gluten, but says it still does not reach 20 ppm or less, the US definition of gluten-free.

How far short does it fall? Gluten Free Watchdog, an independent testing organisation, tested a bakery’s country sourdough loaf and found about 104,000 ppm of gluten. Two other wheat sourdough products it tested, one of them sold as “gluten neutralized,” came in above the upper limits of the tests used (more than 84 ppm and more than 283 ppm, depending on the method), and Gluten Free Watchdog says the true levels were likely much higher.

For comparison, the FDA’s gluten-free limit is less than 20 ppm.

What about the studies showing fermented wheat was safe?

This is where the myth comes from, so it’s worth looking closely.

In a 2011 study published in Clinical Gastroenterology and Hepatology, Italian researchers led by Luigi Greco fermented wheat flour with a selected mix of sourdough lactobacilli plus fungal proteases (protein-digesting enzymes), under controlled conditions, to break down gluten. They then fed baked goods to 16 people with celiac disease for 60 days.

• People given baked goods from ordinary wheat flour (about 80,127 ppm gluten): two of six dropped out because of symptoms.
• People given extensively hydrolysed baked goods, with about 2,480 ppm of gluten left: no symptoms, but they developed damage to the lining of the small intestine (subtotal villous atrophy).
• People given fully hydrolysed baked goods, with about 8 ppm of gluten left: no symptoms, stable antibody levels and no signs of intestinal damage.

So the study showed something interesting: a specialised, lab-controlled process could reduce gluten to below 20 ppm. But look at the middle group. Bread with 97% of its gluten broken down, still a huge reduction, caused intestinal damage without causing symptoms. That is exactly why “I feel fine after sourdough” is not a safe test for someone with celiac disease.

And none of this applies to home or bakery sourdough. An ordinary starter does not contain those selected strains or fungal enzymes, and an ordinary fermentation does not run under those conditions. As Gluten Free Watchdog points out, the fully hydrolysed products from this research are not commercially available. The authors themselves called for longer trials to confirm safety.

What does the FDA say about gluten-free labelling?

The FDA’s 2013 rule says a food labelled “gluten-free” must contain less than 20 ppm of gluten and generally cannot contain wheat, rye, barley or their crossbred grains unless they have been processed to remove gluten to below that level.

Fermented foods are a special case. The FDA explains that the standard tests (sandwich ELISA) do not adequately detect gluten in fermented and hydrolysed foods, because fermentation breaks gluten into smaller fragments that those tests can miss. So in 2020 the FDA finalised a rule for fermented and hydrolysed foods. To use a gluten-free label, a manufacturer must keep records showing that:

1. the food met the gluten-free definition, including less than 20 ppm gluten, before fermentation or hydrolysis;
2. the potential for gluten cross-contact during processing was adequately evaluated; and
3. where needed, measures were taken to prevent gluten getting in.

In plain terms: a sourdough bread can be labelled gluten-free in the US only if it started out gluten-free. Fermenting wheat does not qualify. Beyond Celiac also warns that some brands have falsely claimed their wheat sourdough is safe for people with celiac disease, so trust the gluten-free label, not marketing language like “low gluten” or “gluten neutralised.”

Is sourdough OK for gluten sensitivity or IBS?

People with non-celiac gluten sensitivity or IBS are a different case from celiac disease. Some report tolerating long-fermented sourdough better, possibly because fermentation reduces FODMAPs, which are a common trigger for IBS symptoms. We cover that research in is sourdough bread healthy?

But reduced is not removed. Sourdough still contains gluten, so if you have been told to avoid it, talk to your doctor before experimenting.

How to get truly gluten-free sourdough

Gluten-free sourdough exists, and it can be very good. It just has to be gluten-free from the start.

Buying it:

• Look for a “gluten-free” label, which under FDA rules means the ingredients were gluten-free before fermentation.
• Be wary of bakery loaves described as “low gluten,” “gluten friendly” or “fermented so the gluten is gone.” Those are not gluten-free claims.
• Ask whether it is made in a dedicated gluten-free facility; shared equipment means a risk of cross-contact.

Baking it at home:

• Start a gluten-free starter. You cannot convert a wheat starter: it will always carry wheat. Start fresh with gluten-free flour. Brown rice flour is a common choice, and King Arthur Baking publishes a gluten-free starter made with its Gluten-Free Measure for Measure flour that typically becomes active in 5 to 10 days.
• Use gluten-free flours, such as brown rice, sorghum, buckwheat (despite the name, not related to wheat), millet, teff and certified gluten-free oats, usually with psyllium husk to give the dough structure. Gluten-free sourdough bakes differently from wheat sourdough, so follow a recipe written for it.
• Prevent cross-contact. Use separate jars, bowls, utensils, bannetons and towels, and clean surfaces thoroughly. Wheat flour lingers in the air and on equipment.

The basic rhythms of starter care still apply. Our guides to making a starter from scratch and the sourdough beginner’s guide explain how fermentation works, even though the flours and recipes for gluten-free baking are different.

The bottom line

Wheat sourdough is a lovely bread, and some people find it easier to eat. But it is not gluten-free, and the studies that got fermented wheat below 20 ppm used a specialised lab process you will not find in a bakery. If you have celiac disease, choose sourdough that is labelled gluten-free, or bake your own from gluten-free ingredients in a kitchen you trust.