Deep Frying Gluten: Does It Survive?

Gluten is a protein found in grains like wheat, rye, and barley. For those with gluten intolerance or sensitivity, eating gluten can cause intestinal distress ranging from discomfort to agonizing pain. For people with celiac disease, even the smallest amount of gluten can cause severe intestinal damage and increase the risk of cardiovascular disease and other serious medical conditions. As a result, it is crucial for those with gluten intolerance or celiac disease to avoid gluten cross-contamination when eating out or cooking at home. One common question that arises is whether gluten can survive a deep fryer.

Gluten-free foods cooked in shared fryers with wheat

A study by Thompson et al. (2021) assessed the gluten levels of fries cooked in shared fryers with wheat-containing foods. The study found that 25% of the fry orders would not be considered gluten-free, with gluten levels ranging from 7 to >270 ppm.

Another study by Damasceno and Zandonadi looked at the risk of gluten cross-contamination in shared kitchen environments. The study found that shared utensils and equipment, such as fryers, generally did not lead to significant gluten contamination if appropriate protocols were followed. However, cooking gluten-free and gluten-containing pasta in shared water resulted in gluten levels above the safe limit of 20 ppm.

It is important to note that high heat does not kill or neutralise gluten. Gluten proteins can remain in the fryer and contaminate other foods. Therefore, it is recommended that consumers with coeliac disease or gluten intolerance avoid eating gluten-free foods that have been cooked in shared fryers with wheat-containing foods.

The impact of heat on gluten detection

The Effect of Heat on Gluten

Heat has a significant impact on gluten proteins, causing a series of changes that affect both rheological and biochemical properties. Denaturation, aggregation, and cross-linking occur during heat treatment, altering the native structure of the protein. The specific effects depend on factors such as the parent wheat variety, size, composition, and environmental conditions of the heat treatment. While the exact mechanisms are not yet fully understood, recent research has provided valuable insights.

Gluten Detection in Heated Foods

The detection of gluten in heated foods, such as those cooked in a deep fryer, is a challenging task due to the potential for gluten cross-contact and the limitations of current detection methods. Here are some key points:

• Cross-Contact – Gluten cross-contact is a significant concern in deep frying. Even if the oil is changed, minute particles of gluten can remain in the crevices of the fryer, contaminating subsequent batches of food. This is especially problematic for gluten-sensitive individuals, who can experience intestinal distress and severe intestinal damage from even trace amounts of gluten.
• High Heat Has No Effect on Gluten – It is important to note that high heat does not kill or neutralize gluten proteins. They remain in the fryer, ready to contaminate the next batch of food.
• Detection Methods – The standard method for gluten detection is the enzyme-linked immunosorbent assay (ELISA). However, studies have shown that ELISAs may underperform when analyzing gluten that has been heated. This could be due to decreased solubility of gluten after exposure to high temperatures, as well as structural changes in the gluten proteins.
• The Impact of Heat on Gluten Detection – The impact of heat on gluten detection is twofold. Firstly, heat-induced changes in gluten proteins can affect the accuracy of detection methods like ELISAs. Secondly, heat can facilitate gluten cross-contact in shared fryers, making it difficult to guarantee the gluten-free status of fried foods.
• Recommendations – Due to the risk of cross-contact, it is generally recommended that consumers with celiac disease or gluten sensitivity avoid foods cooked in shared fryers, even if they are labelled as gluten-free. Having a dedicated gluten-free fryer in food establishments can help ensure the safety of gluten-free dishes.

Gluten-free frying temperatures

Frying foods that contain gluten does not make them gluten-free, and can be dangerous for people with Celiac disease. Even when frying oil is heated to a high temperature, gluten proteins will remain in the fryer, waiting to contaminate the next batch of food.

The only way to make gluten safe for people with Celiac disease is a complete breakdown of the peptide chain into its component amino acids. There is some debate about the exact temperature required for this complete breakdown, with one source suggesting that heating food to 315°C (600°F) for 30 minutes may be sufficient. However, at this temperature, the food would be inedible.

The Canadian Celiac Association recommends that people with Celiac disease and gluten sensitivities avoid any food cooked in oil that has also been used for wheat-based products. Cross-contamination can occur when gluten-free foods are cooked in the same fryer as foods containing gluten, even if the oil has just been changed. This is because gluten particles can become lodged in the crevices of a deep fryer.

To avoid cross-contamination, some establishments install a dedicated gluten-free fryer, with rules in place for its use. This can help to give gluten-intolerant diners confidence that their food has been prepared according to strict standards.

When frying gluten-free foods at home, it is important to ensure that the oil has not previously been used to cook foods containing gluten. It is also recommended to use oils with a high smoke point, such as palm kernel oil, peanut oil, sunflower oil, or clarified butter. The ideal frying temperature for gluten-free foods is roughly 350°C. To test if the oil has reached the right temperature without a thermometer, place a chunk of white bread into the hot oil. If it turns golden-brown after exactly one minute, the oil is ready.

How to prevent cross-contamination

To prevent cross-contamination when frying gluten-free foods, it is important to take several precautions:

Firstly, it is essential to understand that gluten molecules can persist in deep fryers even at high temperatures, so a dedicated gluten-free fryer is ideal. If this is not possible, thoroughly clean the fryer before switching to gluten-free foods to prevent contamination. This includes using new ingredients such as butter or oil, as gluten can be transferred between batches.

If cleaning the fryer is not feasible, consider using a deep pan with heated oil and a slotted spoon to cook gluten-free foods separately. This will ensure that gluten particles from other foods do not come into contact with the gluten-free food.

Additionally, when dining out, it is crucial to ask the wait staff or chef about their gluten-free options and how they are prepared. Most restaurants will have a note on the menu about gluten-free alternatives, but it is always good to confirm. Ask how the gluten-free food is cooked and fried, and whether they use a dedicated gluten-free fryer. If the staff are unsure, they can ask the chef or manager for clarification.

Be cautious of restaurants that claim they can cook the gluten out of a dish. As mentioned, gluten is not destroyed by traditional frying methods, as the oil does not reach high enough temperatures.

Finally, be aware that gluten-free fried foods will have a different texture and crunch compared to their glutenous counterparts. This is because gluten is a key factor in creating the crispy texture of fried foods.

How to know if restaurant options are truly gluten-free

Eating out at restaurants can be a minefield for people with coeliac disease or gluten intolerance. Even the smallest amount of gluten can cause intestinal distress, pain, and other serious medical issues. It's important to be vigilant when eating out to avoid cross-contamination and accidental gluten exposure. Here are some tips to help you navigate restaurant options and ensure they are truly gluten-free.

Do Your Research

Before visiting a restaurant, do your research. Look for gluten-free restaurants or those with gluten-free options. There are several apps and websites available, such as FindMeGlutenFree, TripAdvisor, Yelp, and Zomato, that can help you find gluten-free-friendly restaurants. Read reviews, but be cautious as information can be incorrect or outdated. Cross-reference multiple sources and, if possible, reach out to the restaurant directly to inquire about their gluten-free options and procedures to avoid cross-contamination.

Ask the Right Questions

When speaking to restaurant staff, ask specific questions to determine if their gluten-free options are safe for you. Inquire about dedicated gluten-free fryers, separate cooking areas, and clean utensils. Ask if they use separate oils for gluten-free items and if there is a risk of gluten crumbs or particles contaminating your food. Be cautious of fried foods, as gluten particles can be difficult to remove from fryer oil, even with filtration.

Communicate Your Needs

Be open and clear about your dietary restrictions. Inform the restaurant staff that you have coeliac disease or gluten intolerance and that even a small amount of gluten can cause adverse effects. Explain the importance of avoiding cross-contamination and ask for their assistance in ensuring your meal is gluten-free. A good restaurant will take your needs seriously and be happy to accommodate you.

Choose the Right Dishes

When ordering, opt for dishes that are inherently gluten-free, such as grilled meats, vegetables, or salads. Avoid fried foods unless the restaurant has a dedicated gluten-free fryer. Be cautious of dishes with multiple ingredients, as the risk of cross-contamination increases. Opt for simple dishes and ask for confirmation from the kitchen that your meal is gluten-free before consuming it.

Stay Informed

Stay up to date with the latest information and guidelines on gluten-free dining. Follow gluten-free bloggers, join online communities, and subscribe to newsletters that provide accurate and reliable information. This will empower you to make informed decisions when dining out and reduce the risk of accidental gluten exposure.

Remember, when in doubt, it is always best to err on the side of caution. Your health is a priority, and by taking these proactive steps, you can enjoy dining out while maintaining a gluten-free diet.

Frequently asked questions