A Guide to Which Thickeners Are Not Gluten Free

November 9, 2025 •

4 min read

In the United States, labeling laws mandate that if an ingredient is derived from a gluten-containing grain, the source must be declared. For those with celiac disease or gluten sensitivity, knowing which thickeners are not gluten free is crucial for safely navigating ingredient lists on processed foods, as gluten can hide in unexpected places.

Quick Summary

This guide details thickeners containing gluten, such as wheat flour and ambiguously labeled starches. It explains how to identify hidden sources like malt and dextrin and safely navigate ingredient lists.

Key Points

Hidden Gluten: Gluten often hides in processed foods as thickeners, including soups, sauces, and desserts.
Wheat and Grain Thickeners: Thickeners like wheat flour, barley malt, and rye flour are unsafe for a gluten-free diet.
Modified Starch: If "modified food starch" is not labeled as gluten-free, it should be avoided as it may be derived from wheat.
Malt Derivatives: Ingredients containing barley malt extract or flavorings should be avoided unless explicitly labeled gluten-free.
Label Reading is Key: Always check ingredient lists, as products that seem safe may contain hidden gluten, like traditional soy sauce.
Cross-Contamination: Prevent cross-contamination in the kitchen by using separate utensils and avoiding shared items.
Certification Matters: Rely on certified gluten-free products when dealing with high-risk ingredients like oats or modified starches.

Understanding the Gluten in Thickeners

For anyone on a gluten-free diet, avoiding obvious sources of gluten like bread and pasta is a first step. However, the use of thickeners in a vast array of processed foods means gluten can show up in unexpected places, from sauces and soups to desserts. Understanding which thickeners are unsafe and learning to read labels with a critical eye is key to maintaining a safe diet. The primary risk comes from thickeners derived from wheat, barley, and rye, which are the main gluten-containing grains.

Common Thickeners to Avoid

Wheat Flour: This is the most common thickener and is a primary ingredient in a traditional roux, a base for many gravies and sauces. Any food thickened with standard all-purpose flour contains gluten and must be avoided. This includes many pre-packaged gravies, canned soups, and creamy sauces.
Barley Malt Extract: Often used for flavoring, malt is derived from barley and is not gluten-free. It appears in a variety of foods, including some cereals, chocolate, and malted milk, so it's important to check labels carefully. The term "malt" on a label should always be treated as a red flag for gluten.
Rye Flour: While less common than wheat, rye flour is also a gluten-containing grain that may be used as a thickener in some dishes.

The Ambiguity of Starches and Derivatives

Many thickeners are derived from starches, which can come from a variety of sources. While starches like corn, potato, and tapioca are naturally gluten-free, their labeling can be confusing, and some processed varieties are not safe.

Wheat Starch: A Major Source of Confusion

Wheat starch is a particularly problematic ingredient. Although it can be processed to remove gluten, the amount remaining can vary significantly.

In the United States, certified gluten-free products do not use wheat starch.
In Europe, wheat starch may be used in foods labeled "gluten-free" if it meets the regulatory threshold of less than 20 parts per million (ppm) of gluten.
However, many celiac patients and those with a high sensitivity still choose to avoid it completely due to the potential for residual gluten and the risk of long-term harm.

The Puzzle of Modified Food Starch

Another confusing term is "modified food starch." This is a general term for starch that has been altered chemically or physically for various functions, like thickening and stabilizing.

The source matters: Modified food starch can be derived from safe sources like corn, tapioca, or potato, or from unsafe sources like wheat.
Read the label carefully: If the modified food starch is derived from wheat, it must be listed as "modified food starch (from wheat)" in some countries. If the source is not specified, it is safest to assume it could be wheat-based and avoid the product unless it is certified gluten-free.

Hidden Dextrins and Flavorings

Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch.

Wheat dextrin: If a dextrin is made from wheat, it will contain gluten and is not safe.
Maltodextrin: While maltodextrin can be made from wheat, the processing often removes the gluten. However, the source is still critical, and it should be avoided unless the product is certified gluten-free.
Soy Sauce: Traditional soy sauce is typically made from fermented wheat and soybeans, making it a hidden source of gluten. Always opt for certified gluten-free tamari or other labeled gluten-free alternatives.

Comparison: Gluten-Containing vs. Gluten-Free Thickeners


Feature	Gluten-Containing Thickeners	Gluten-Free Thickeners
Source	Wheat flour, barley, rye	Cornstarch, tapioca starch, arrowroot, guar gum
Example Uses	Traditional gravies, roux, malted cereals	Sauces, pie fillings, baking, dairy-free products
Hidden Sources	Modified food starch (unless labeled GF), some dextrins, malt extract, traditional soy sauce	Safe when certified, but cross-contamination can occur
Best Practice	Avoid completely if gluten-sensitive or celiac	Look for certified products, especially for oat flour

Avoiding Cross-Contamination

Even when using gluten-free ingredients, cross-contamination is a serious concern, especially for those with celiac disease.

Kitchen Habits: If you share a kitchen with someone who uses gluten, use separate utensils, cutting boards, and cooking surfaces. Avoid dipping utensils used for gluten items into gluten-free condiments or sauces.
Manufacturing Risks: Be mindful of products that are not explicitly labeled gluten-free, even if the primary ingredients seem safe. Oats, for instance, are naturally gluten-free but are often processed in facilities that also handle wheat, leading to cross-contamination. This is why certified gluten-free oats are essential for a safe diet.

Conclusion

The world of food thickeners is complex, and vigilance is required to avoid hidden gluten. The most critical step is to always read the full ingredient list, not just the product name or claims. By understanding which thickeners are not gluten-free—like wheat flour, malt, certain starches, and traditional soy sauce—and knowing how to spot ambiguous ingredients like "modified food starch," you can confidently and safely manage your diet. The rise of certified gluten-free products has made this easier, but careful label reading remains the best defense against accidental gluten exposure.

For more in-depth information and resources on managing a gluten-free lifestyle, consider consulting the Celiac Disease Foundation.

Frequently Asked Questions

No, modified food starch is not always gluten-free. It can be made from various sources, including wheat. Unless the label specifies a gluten-free source (like corn or tapioca) or the product is certified gluten-free, it is safest to assume it is unsafe.

A roux is a cooking thickener made from equal parts fat (like butter) and flour. Since traditional roux uses wheat flour, it is not gluten-free and must be avoided.

Yes, many gluten-free flour blends can be used as a thickener, just like traditional flour. It's often recommended to create a slurry with cold water first to prevent clumping.

Wheat starch is not naturally gluten-free. While it can be processed to remove most gluten, the amount remaining can be a risk for sensitive individuals. In the US, it is not used in certified gluten-free products.

You can thicken gravy with gluten-free alternatives such as cornstarch, arrowroot powder, or a slurry made from a certified gluten-free flour blend.

No, dextrins are not all gluten-free. They can be made from wheat, and products containing wheat-derived dextrins should be avoided unless they are certified gluten-free.

Traditional soy sauce is fermented with wheat and therefore contains gluten. Always choose a certified gluten-free tamari or a soy sauce explicitly labeled as gluten-free.