Ingredients
- 2 large red onions, thinly sliced
- 1 cup apple cider vinegar
- ½ cup water
- 2 tablespoons granulated sugar
- 1½ teaspoons kosher salt
- 2 cloves garlic, thinly sliced
- 1 teaspoon whole black peppercorns
- ½ teaspoon mustard seeds
- ½ teaspoon crushed red pepper flakes
- 1 bay leaf
- 1 tablespoon fresh lime juice
A quick note on ingredient choices: apple cider vinegar is preferred over white vinegar here for its slightly fruitier, more rounded acidity that complements the onion’s natural sweetness rather than overpowering it. If you prefer a sharper, more classic tang, white vinegar or a mix of the two can be substituted. Kosher salt dissolves cleanly without additives that could cloud the brine, and fresh lime juice at the end adds a bright, citrusy finish that pairs especially well with the Mexican and Tex-Mex dishes these onions are so often served alongside.
Instructions
Peel the red onions and slice them into thin, even rings or half-moons. Slicing the onions as thinly and evenly as possible ensures they pickle quickly and consistently, and it also gives you that classic, delicate texture that’s easy to pile onto tacos, sandwiches, and salads.
Pack the sliced onions tightly into a clean glass jar, leaving a little space at the top. Packing them snugly helps the onions stay submerged in the brine once it’s poured over, and it also allows you to fit a generous amount of onion into a single jar.
In a small saucepan, combine the apple cider vinegar, water, granulated sugar, kosher salt, garlic, black peppercorns, mustard seeds, crushed red pepper flakes, bay leaf, and fresh lime juice.
Bring the mixture to a gentle simmer over medium heat, stirring until the sugar and salt have completely dissolved. You’ll know the brine is ready once it looks clear (aside from the visible garlic and spices) and no longer feels gritty when tested with a spoon.
Carefully pour the hot pickling liquid over the onions until they are completely submerged. Unlike some pickle recipes that call for cooling the brine first, pouring it hot over thinly sliced onions is intentional here — it helps soften the onions just slightly while jump-starting that vivid pink color transformation.
Press the onions gently with a clean spoon to release any trapped air bubbles and ensure every slice is covered with the brine. This step helps guarantee even pickling throughout the jar.
Allow the jar to cool uncovered to room temperature. Leaving the jar uncovered while it cools helps prevent excess condensation from building up inside once it’s sealed.
Seal tightly and refrigerate for at least 1 hour before serving. For deeper flavor and a brighter color, refrigerate for 24 hours. While these onions are ready to eat surprisingly quickly, letting them sit longer allows the flavors to fully develop and the color to reach its most vibrant point.