How is Gluten Removed From Stout? The Brewing Methods Explained

December 3, 2025 •

4 min read

An estimated 6% of the population is affected by gluten sensitivity, driving a growing market for gluten-free products, including dark beers. Brewers achieve this by either brewing a stout with naturally gluten-free ingredients or by treating a traditional stout to remove gluten after fermentation.

Quick Summary

Stout brewers use two main methods to eliminate gluten: either using naturally gluten-free grains or applying specific enzymes during the brewing process. This results in either a genuinely gluten-free stout or a gluten-reduced product, with different safety implications for consumers with celiac disease.

Key Points

Two Primary Methods: Brewers can make stouts gluten-free by either using naturally gluten-free grains or by adding an enzyme to break down gluten in a traditional barley base.
Alternative Grains for True Gluten-Free: Ingredients like millet, sorghum, buckwheat, and rice are used to brew genuinely gluten-free stouts, suitable for people with celiac disease.
Enzymatic Treatment for Gluten-Reduced: Enzymes like Brewers Clarex® are added during fermentation to break down gluten proteins, but this results in a 'gluten-reduced' product, not a truly gluten-free one.
Safety Depends on Method: Certified gluten-free stouts made with alternative grains are the safest option for those with celiac disease, while gluten-reduced stouts may still cause a reaction.
Flavor Profiles Vary: Stouts made with alternative grains may have a distinct flavor, while the enzymatic method preserves the traditional barley stout flavor.
Risk of Cross-Contamination: Brewers must prevent cross-contamination in facilities that produce both gluten-free and gluten-containing beers.

Brewing a Truly Gluten-Free Stout with Alternative Grains

The most straightforward method for creating a completely gluten-free stout is to use ingredients that contain no gluten from the start. Traditional stouts rely on malted barley for their roasted, dark character, and this is where the gluten originates. By replacing barley with naturally gluten-free alternatives, brewers can produce a stout that is safe for people with celiac disease and other severe gluten sensitivities. This method also requires a dedicated facility or strict measures to prevent cross-contamination from gluten-containing products.

Key Ingredients for Gluten-Free Stouts

Millet: This ancient grain can be malted and roasted to provide a flavor profile surprisingly similar to barley, offering notes of nuts and malt.
Sorghum: Often used as a base for many gluten-free beers, sorghum can provide fermentable sugars. Sorghum syrup or malt is commonly used.
Buckwheat: Despite its name, buckwheat is not a wheat and is gluten-free. It can add an earthy, robust flavor to the stout.
Rice: Roasted rice malt or rice hulls can be used to add fermentable sugars and aid in the lautering process.
Oats: Certified gluten-free oats can provide the silky, smooth mouthfeel characteristic of an oatmeal stout.

Brewing with Alternative Grains

Because these grains lack the enzymes found in barley, brewers must add exogenous enzymes, such as amylase, during the mashing process to break down starches into fermentable sugars. The brewing process must be carefully controlled, especially the mashing temperature, to ensure proper starch conversion. Additionally, brewers must use a yeast strain that works effectively with the chosen gluten-free grains.

Creating a Gluten-Reduced Stout with Enzymes

A second method allows brewers to use traditional gluten-containing grains, like barley, and then use an enzyme to break down the gluten proteins. The most common enzyme used for this purpose is a proline-specific endo-protease derived from Aspergillus niger, often sold under the trade names Brewers Clarex® or Clarity Ferm®.

The Enzymatic Treatment Process

The enzyme is added during the fermentation phase of brewing.
It works by cleaving the gluten proteins into smaller peptide fragments.
This reduces the gluten to levels below the 20 parts per million (ppm) threshold required by international standards for labeling as 'gluten-free' in some regions, though it is labeled 'gluten-reduced' in the US.
This method has the advantage of preserving the traditional taste and mouthfeel of a barley-based stout, as the flavor-producing compounds are not affected.

However, it's crucial to note the distinction: a 'gluten-reduced' stout is not guaranteed to be safe for those with celiac disease, as some individuals can still react to the smaller gluten fragments.

Comparison of Gluten-Free vs. Gluten-Reduced Stout Production


Feature	Gluten-Free Stout (Alternative Grains)	Gluten-Reduced Stout (Enzymatic)
Starting Ingredients	Naturally gluten-free grains (millet, sorghum, buckwheat, rice).	Traditional gluten-containing grains (barley).
Gluten Content	Inherently free of gluten from the start.	Contains gluten initially, reduced to <20 ppm in final product.
Brewing Process	Requires specialized mash procedures and exogenous enzymes.	Standard brewing process, with enzyme added during fermentation.
Flavor Profile	Can have a different flavor profile from traditional stouts.	Maintains a traditional stout flavor profile.
Safety for Celiacs	Generally considered safe, assuming no cross-contamination.	Not recommended for those with celiac disease due to potential reactions.
Labeling (USA)	Can be certified "gluten-free".	Labeled "gluten-reduced" or "crafted to remove gluten".
Cross-Contamination	Risk of cross-contamination must be managed carefully.	No risk of cross-contamination if standard ingredients are used throughout.

The Brewing Process for a Gluten-Reduced Stout

Milling and Mashing: Traditional barley is milled and mashed in the standard stout brewing process to create the dark, roasty wort base.
Boiling: The wort is boiled to sanitize, add hops, and develop bitterness and flavor compounds.
Fermentation and Enzyme Addition: The wort is cooled, and yeast is pitched along with the gluten-reducing enzyme, such as Clarity Ferm®. The enzyme works to cleave gluten proteins during this phase.
Maturation and Testing: The stout is allowed to mature. After fermentation, the gluten levels are tested using a competitive R5 ELISA to ensure they are below the 20 ppm threshold.
Packaging: The finished product is packaged and labeled appropriately, as per regional food and beverage regulations.

A Note on Contamination and Safety

For breweries producing both gluten-containing and gluten-free beers, cross-contamination is a significant concern that must be managed through strict protocols. For individuals with celiac disease, a truly gluten-free product made from alternative grains is the safest choice. A 'gluten-reduced' product, while suitable for some with less severe sensitivities, should be approached with caution by anyone with a medical diagnosis like celiac disease.

Conclusion

Removing gluten from stout is a process that can be approached in two distinct ways: using naturally gluten-free ingredients from the outset or utilizing specialized enzymes to break down gluten proteins in a traditional barley-based brew. While the latter method, producing 'gluten-reduced' beer, offers a taste profile closer to conventional stout, it carries a higher risk for individuals with severe gluten sensitivities. For guaranteed safety and a completely gluten-free experience, a stout crafted entirely from alternative grains like millet, sorghum, and rice is the definitive choice. The choice between these methods depends on the target consumer and the level of gluten avoidance required. Understanding these processes is essential for both brewers creating the product and consumers making informed dietary decisions.

Learn more about the differences between these types of brews from the American Homebrewers Association.

Frequently Asked Questions

A 'gluten-free' stout is brewed using only ingredients that contain no gluten, such as millet and sorghum. A 'gluten-reduced' stout is brewed with traditional gluten-containing grains like barley, but an enzyme is added to break down gluten to a level below 20 ppm.

No, gluten-reduced stout is not recommended for people with celiac disease. The enzyme breaks gluten into smaller fragments, which may not be detected by standard tests but can still trigger an immune response in some individuals.

Brewers use a proline-specific endo-protease enzyme, such as Brewers Clarex® or Clarity Ferm®, to break down the gluten proteins in barley-based wort during fermentation.

Brewers make a naturally gluten-free stout by using a malt bill consisting of alternative grains like millet, roasted buckwheat, and rice. They may also need to add supplemental enzymes during the mash.

The impact on taste depends on the method. The enzymatic method is designed to preserve the traditional flavor profile. Using alternative grains can result in a different, though not necessarily inferior, flavor profile compared to a traditional barley stout.

Internationally, the threshold for labeling a product as 'gluten-free' is typically less than 20 ppm of gluten. However, specific labeling regulations vary by country, with the U.S. requiring beers made with traditional grains to be labeled as 'gluten-reduced' even if they test below this level.

To prevent cross-contamination, breweries should either use a dedicated, gluten-free facility or implement strict procedures for separating ingredients, equipment, and cleaning practices when making both gluten-free and regular beers.