Sourdough King: Allergens at a Glance
The honest verdict
Sourdough King · Burger King
The Sourdough King is a Burger King premium burger featuring a thick, toasted sourdough bun, a quarter-pound beef patty, melted American cheese, crispy bacon, lettuce, tomato, and mayonnaise. The allergen profile is anchored by wheat from the sourdough bun, milk from the cheese and mayo, and egg from the mayonnaise. Soy may be present in refined oils and condiments. Sesame may appear on the bun or in sauces. Peanut, tree nut, fish, and shellfish are not typical ingredients. The sourdough bun differentiates this sandwich from the Whopper (sesame seed bun) and the Original Chicken Sandwich (brioche-style bun). Cross-contact via shared grills and prep surfaces is possible. Always confirm with your specific Burger King location before ordering.
Allergen details change and vary by location. This is a general guide — always confirm with the restaurant before ordering. Not official or medical advice.
Key facts
The Sourdough King's toasted sourdough bun is wheat-based, making it a direct source of gluten.
FDA — Food Allergen Labeling and Consumer Protection Act (FALCPA)
Mayonnaise in the Sourdough King contains egg and milk derivatives, adding two allergens beyond the cheese.
Sesame became the 9th major food allergen under the FASTER Act in 2023 — check sourdough bun ingredients at your location.
Every major allergen, one clear grid
Each of the nine major allergens marked for Sourdough King at Burger King — Contains, May contain (cross-contact or varies), or Free. Anything we couldn't confirm defaults to "may contain," because a shared kitchen can't be ruled out without the restaurant's official menu.
- MilkContains
American cheese is a direct source of milk. Mayonnaise also contains milk derivatives in some formulations. The sourdough bun may contain milk or butter. Milk is present in multiple components of this sandwich.
- EggContains
Mayonnaise is made with egg yolks. The sourdough bun may also contain eggs. Egg is a confirmed ingredient in this sandwich.
- Wheat / GlutenContains
The toasted sourdough bun is wheat-based. This is the primary source of gluten in the sandwich. There is no standard gluten-free bun option at Burger King.
- SoyMay contain
Refined soybean oil is commonly used in Burger King kitchens for cooking and in mayonnaise and other sauces. Highly refined soy oil is FDA-exempt from allergen labeling and tolerated by most with soy allergy. Those with severe soy sensitivity should confirm the specific oil and sauce ingredients used.
- PeanutFree
Peanut is not a listed ingredient in the Sourdough King components. Peanut oil is not standard in Burger King burger preparation. Cross-contact is very unlikely.
- Tree NutFree
Tree nuts are not an ingredient in the sourdough bun, beef patty, cheese, bacon, or standard condiments at Burger King.
- FishFree
Fish is not an ingredient in the Sourdough King. Burger King does not fry fish items in the same oil as burger patties, so cross-contact is not a concern for this sandwich.
- ShellfishFree
Shellfish is not an ingredient in this sandwich and is not typical in Burger King burger preparation environments.
- SesameMay contain
The sourdough bun may contain sesame seeds or sesame flour. Some Burger King locations use sesame oil in their kitchen. Sesame is now a required allergen under the FASTER Act — check with your location whether the sourdough bun contains sesame.
“May contain” means cross-contact is possible or the answer varies by location — not that the allergen is a listed ingredient. For a severe allergy, treat “may contain” the same as “contains” until the restaurant confirms otherwise.
Small changes that remove an allergen
Simple modifications that can take an allergen off your sourdough king. Always name your allergy when you order and ask staff to confirm — a modification only helps if the kitchen prepares it separately.
Order without cheese
Order without mayonnaise
Request a lettuce wrap instead of the sourdough bun
Ask for the sandwich on a plain bun without sesame
A modification lowers exposure but doesn't erase cross-contact from shared fryers, grills, or prep surfaces. For a severe allergy, confirm the prep with a manager before you eat.
Read this before you order
Cross-contact & severe allergies
A “free of” mark on the grid above means the allergen isn't an ingredient — it doesn't mean the item was made in an allergen-free kitchen. Two things matter most:
Shared fryers & equipment
Burger King grills and prep surfaces are shared across all burger and sandwich items. The same spatula, grill surface, and prep area may contact the Whopper (sesame seed bun), the Original Chicken Sandwich (brioche bun), and the Sourdough King. Cross-contact risk for wheat, milk, egg, and sesame is present through shared equipment. Ask staff about dedicated prep surfaces at your specific location.
If your allergy is severe
For anaphylactic allergy to wheat, milk, egg, or sesame, the Sourdough King is not a safe choice without restaurant-level confirmation. Multiple components contain these allergens, and shared grills introduce cross-contact risk. Carry your epinephrine auto-injector. If you cannot confirm preparation details, consider a plain beef patty without the bun or a salad option instead.
This guidance is general and can't account for how any single location prepares your food. The restaurant's staff and official allergen menu are the final word — when in doubt, ask, or choose something else.
❓Frequently Asked Questions
The Sourdough King uses a thick sourdough bun, while the Whopper uses a sesame seed bun. The Whopper's sesame seed bun is a direct source of sesame, whereas the Sourdough King's bun may or may not contain sesame depending on the location. Both contain milk (cheese) and egg (mayo). The Whopper typically includes ketchup and pickles; the Sourdough King adds bacon. The core allergen profile is similar, but the bun type changes the sesame risk.
Yes. The toasted sourdough bun is wheat-based and contains gluten. There is no standard gluten-free bun option at Burger King. A lettuce wrap or bunless preparation removes the wheat, but cross-contact from shared grills and prep surfaces may still introduce trace gluten. If you have celiac disease or severe gluten sensitivity, confirm with the restaurant whether a dedicated prep area is available.
Not without modifications. The American cheese is a direct source of milk. Mayonnaise also contains milk derivatives. The sourdough bun may contain milk or butter. Removing the cheese and mayo reduces the milk risk significantly, but the bun may still contain dairy. Ask the restaurant whether their sourdough bun is dairy-free. If you have a severe milk allergy, consider a bunless option or a different menu item.
It may. The sourdough bun at some Burger King locations contains sesame seeds or sesame flour. Sesame is now a required allergen under the FASTER Act (effective January 2023). Check with your specific Burger King location whether their sourdough bun contains sesame. If sesame is a concern, ask about a plain bun option without sesame.
The Sourdough King is typically ordered as a standalone sandwich, but if you add fries or onion rings, note that Burger King's fries are cooked in shared fryers with breaded items (wheat cross-contact). Onion rings contain wheat. Dipping sauces like ranch (milk, egg), honey-mustard (egg, soy), and BBQ (soy) add separate allergen sources. Evaluate each side and sauce independently.
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Please verify before ordering
Allergen info changes and varies by location
Recipes, suppliers, and preparation methods change often and differ between locations, so the details here can go out of date or not match your specific Burger King restaurant. Always confirm directly with the restaurant and check its official allergen menu before ordering. This page is a general research summary — it is not official information from Burger King, and it is not medical advice. If you have a food allergy, decisions about what is safe to eat should be made with the restaurant and, where relevant, your healthcare provider.