What Does Gluten Do to Soy Sauce? Flavor, Fermentation & Alternatives

January 14, 2026 •

2 min read

Traditional soy sauce has been brewed with a mix of soybeans and wheat for centuries, with the wheat playing a crucial role in the fermentation process. This is surprising to many, but it is precisely what introduces gluten into the finished product, impacting its flavor profile while making it unsuitable for a gluten-free diet.

Quick Summary

Wheat is a key ingredient in traditional soy sauce, where its carbohydrates contribute to the sauce's complex aroma and flavor during fermentation. It also introduces gluten, which is broken down into fragments during brewing but remains present, making it unsafe for those with celiac disease.

Key Points

Flavor Enhancement: Wheat adds aroma and sweetness to traditional soy sauce during fermentation.
Incomplete Gluten Breakdown: Fermentation reduces gluten, but it remains, so traditional soy sauce is not gluten-free.
Celiac Risk: Residual gluten makes regular soy sauce unsafe for those with celiac disease or sensitivity.
Tamari is an Alternative: Many tamari varieties are naturally gluten-free, using only soybeans, but check the label.
Look for Certification: Certified gluten-free soy sauces use other grains like rice instead of wheat.
Other Options Exist: Coconut aminos or liquid aminos provide gluten-free, soy-free substitutes.

The Role of Wheat and Gluten in Traditional Soy Sauce

Traditional soy sauce (shoyu) is made from a blend of soybeans, roasted and crushed wheat, salt, and water. The wheat is essential to the brewing method and impacts the final taste and aroma. During the fermentation period, enzymes break down both soy proteins and wheat components.

The Fermentation Process

Enzymes break down the gluten proteins in wheat into smaller fragments, while starches are converted into simple sugars. These sugars are then fermented by bacteria and yeast, producing lactic acid and alcohol.

How Gluten Affects Flavor

Although gluten is significantly broken down, the wheat's components contribute to the sauce's flavor. This includes providing a fine aroma, subtle sweetness, and contributing to the rich, dark color and complex umami taste.

The Health Implications for Gluten Sensitivity

Despite fermentation, traditional soy sauce contains residual gluten and is not considered gluten-free. Standard testing cannot reliably ensure levels below the gluten-free threshold of 20 ppm. Therefore, it is unsafe for individuals with celiac disease or severe gluten intolerance.

The Difference Between Regular and Gluten-Free Soy Sauces


Aspect	Regular (Wheat-Based) Soy Sauce	Gluten-Free Soy Sauce & Tamari
Primary Ingredients	Soybeans, roasted wheat, water, salt, koji culture	Soybeans, water, salt, koji culture (some tamari); or rice, soybeans, salt, water (some gluten-free)
Flavor Profile	Balanced, complex aroma, and slight sweetness from wheat	Often richer, less complex than shoyu; tamari has a deeper umami profile
Color	Reddish-brown	Darker brown
Texture	Thinner, lower viscosity	Often thicker, with higher viscosity, especially tamari
Allergen Status	Contains gluten and is not safe for gluten-sensitive individuals	Gluten-free, safe for those with celiac disease and gluten intolerance
Best For	All-purpose cooking, marinades, dipping sauces	All-purpose cooking, dipping sauces, especially for sushi

Gluten-Free Alternatives to Traditional Soy Sauce

For a gluten-free diet, several alternatives offer a similar savory, umami flavor:

Tamari

Tamari is typically brewed solely from soybeans without wheat, though checking labels is advised as some brands may include it. Certified gluten-free tamari is available.

Certified Gluten-Free Soy Sauce

Many brands offer certified gluten-free soy sauces using gluten-free grains like rice instead of wheat. Look for a certified label.

Coconut Aminos

Coconut aminos are a gluten-free and soy-free option made from fermented coconut blossom sap and salt, providing a savory flavor.

Liquid Aminos

Liquid aminos are unfermented liquid protein concentrates from processed soybeans, offering a salty, savory taste. Check labels for certification.

Conclusion: Making the Right Choice for Your Diet

Wheat adds flavor to traditional soy sauce but introduces gluten, making it unsuitable for those with celiac disease or sensitivity. Numerous safe gluten-free alternatives exist, including tamari, certified gluten-free soy sauces, and coconut aminos. Checking labels is crucial.

Frequently Asked Questions

No, fermentation breaks down gluten proteins, but enough remains to be unsafe for people with celiac disease or gluten sensitivity.

Adding roasted wheat introduces starches essential for developing the sauce's complex aroma, sweetness, and deep flavor profile during fermentation.

Tamari is often a reliable substitute as it's traditionally made with only soybeans. However, some brands might add wheat, so always check the label for a 'gluten-free' certification.

No, people with celiac disease should not consume traditional soy sauce due to residual gluten traces.

Look for a 'Certified Gluten-Free' label on the packaging and check the ingredient list to confirm no wheat is present.

Gluten-free alternatives include certified gluten-free soy sauce, tamari, coconut aminos (soy-free), and liquid aminos.

Most traditional varieties of both contain wheat and gluten. Traditional Japanese tamari is often wheat-free, and many brands offer specific gluten-free versions.