Subway Sweet Onion Sauce Copycat Recipe

Sharing is caring!

This Subway Sweet Onion Sauce copycat is sweet, tangy, and packed with onion flavor, with a light glossy texture that makes it easy to drizzle over sandwiches and wraps. It uses sugar, vinegar, onion, mustard, and a small amount of cornstarch to create a sauce that’s much closer to a vinaigrette-style condiment than a creamy sandwich dressing.

The important part is not over-thickening it. The sauce should still pour easily when cold, so take it off the heat once it lightly coats a spoon. It will thicken considerably more as it cools.

I especially like it on homemade subs made with my Subway bread copycat recipe, but it also works with chicken sandwiches, wraps, salads, and grilled vegetables.

What Is Subway Sweet Onion Sauce?

Sweet Onion Sauce is a sweet-and-tangy, onion-forward sandwich sauce associated with Subway. Unlike mayonnaise-based sauces, it has a glossy, pourable consistency and gets most of its flavor from sugar, vinegar, onion, mustard, and seasonings.

This homemade version is inspired by that style of sauce. It is not Sweet Onion Teriyaki, which has a different flavor profile and additional teriyaki-style ingredients.

Ingredients

• 1 cup (200 g) granulated sugar
• ½ cup (120 ml) water
• 6 tablespoons (90 ml) white vinegar
• 4 teaspoons (20 ml) red wine vinegar
• 1 tablespoon (8 g) cornstarch
• 1 tablespoon dried minced onion
• 1 teaspoon finely grated fresh onion
• 1 tablespoon Dijon mustard
• 2 teaspoons dry mustard powder
• 1 teaspoon kosher salt
• 1 teaspoon poppy seeds
• ½ teaspoon celery seed
• ⅓ teaspoon onion powder
• ⅓ teaspoon paprika
• ⅓ teaspoon ground black pepper
• ¼ teaspoon garlic powder

Instructions

1. Make the cornstarch slurry: Remove about 2 tablespoons of the measured water and whisk it with the cornstarch in a small bowl until completely smooth.
2. Combine the sauce: Add the remaining water, sugar, white vinegar, red wine vinegar, dried onion, fresh onion, Dijon mustard, mustard powder, salt, poppy seeds, celery seed, onion powder, paprika, and black pepper to a small saucepan. Whisk to combine.
3. Bring to a simmer: Cook over medium heat, stirring frequently, until the sugar has completely dissolved and the mixture begins to simmer.
4. Thicken the sauce: Whisk the cornstarch slurry again, then slowly pour it into the saucepan while whisking. Reduce the heat and simmer gently for about 2–4 minutes, stirring often, until the sauce looks glossy and lightly coats the back of a spoon.
5. Check the consistency: Don’t cook until the sauce looks thick in the saucepan. It should still be fairly pourable because it will thicken more as it cools. If it becomes too thick, whisk in water 1 tablespoon at a time.
6. Cool: Remove from the heat and let the sauce cool before transferring it to a clean jar or squeeze bottle.
7. Chill before serving: Refrigerate for at least 2 hours before using. The onion and vinegar flavors become more balanced once the sauce has had time to chill.

Tips for the Best Sweet Onion Sauce

• Don’t overcook the cornstarch. The hot sauce should look slightly thinner than you ultimately want it.
• Grate the fresh onion finely. Large onion pieces change the texture and make the sauce harder to squeeze from a bottle.
• Let it chill before judging the flavor. Freshly cooked sauce tastes sharper than it does after a few hours in the refrigerator.
• Stir or shake before serving. The seasonings and onion pieces can settle as the sauce sits.
• Adjust with water, not more vinegar. If the chilled sauce is thicker than you like, stir in a teaspoon or two of water.

How to Use Sweet Onion Sauce

Use it as a sandwich or wrap sauce, drizzle it over grilled chicken, toss a small amount with salad, or serve it as a dipping sauce for chicken and vegetables.

For a homemade Subway-style meal, pair it with my Subway bread copycat recipe.

Storage

Let the sauce cool completely, transfer it to a clean airtight container, and refrigerate promptly.

Because this is a homemade sauce without commercial preservatives and its final acidity hasn’t been laboratory tested, I wouldn’t treat it like a shelf-stable bottled condiment. For the most conservative approach, use it within about 1 week and discard it if you notice mold, fermentation, unusual bubbling, or an off smell.

For longer storage, freeze the cooled sauce in a freezer-safe container, leaving a little room for expansion. Thaw it in the refrigerator and whisk or shake well before using.

FAQ

Is Subway Sweet Onion Sauce the same as Sweet Onion Teriyaki?

No. Sweet Onion Sauce is primarily a sweet-and-tangy onion sauce, while Sweet Onion Teriyaki includes additional teriyaki-style flavors. This recipe is intended to reproduce the lighter Sweet Onion Sauce style rather than Sweet Onion Teriyaki.

Why did my sweet onion sauce get too thick?

Cornstarch continues thickening the sauce as it cools. Remove the pan from the heat while the sauce is still pourable. If the chilled sauce becomes too thick, whisk in a small amount of water until it reaches the consistency you want.

Can I make this sauce sugar-free?

I don’t recommend replacing the granulated sugar with monk fruit, stevia, or another high-intensity sweetener using a simple conversion. Sugar contributes substantial volume and affects the texture of this sauce as well as its sweetness.

A sugar-free version should ideally be developed specifically around the properties of the replacement sweetener.

Is this sauce dairy-free?

Yes. The recipe as written contains no milk, cream, butter, or other dairy ingredients.

Can I make it ahead?

Yes. In fact, the flavor improves after several hours in the refrigerator, so making it earlier in the day or the night before works well.

Sharing is caring!