Ingredients
Here is everything you need for one large jar:
- 2 medium red onions, thinly sliced
- 1 cup white vinegar (5% acidity)
- ½ cup water
- 1 tablespoon granulated sugar
- 1½ teaspoons salt
- 1 garlic clove, peeled and lightly crushed (optional)
- ½ teaspoon black peppercorns
- ½ teaspoon mustard seeds (optional)
- ¼ teaspoon red pepper flakes (optional)
- 1 to 2 tablespoons fresh lime juice (optional, for extra zing)
Ingredient Notes and Smart Substitutions
Red onions: Choose firm, heavy onions with dry, papery skins and no soft spots. Fresh onions give the crispest texture and the brightest color.
White vinegar: Distilled white vinegar with 5% acidity gives a clean, sharp tang and lets the onion color shine. Using vinegar with at least 5% acidity matters for flavor and for keeping the pickles safe in the refrigerator. You can swap in other vinegars if you prefer a different flavor profile:
- Apple cider vinegar: fruity and slightly mellow, but the color may be a little less vibrant
- White wine vinegar: softer and more delicate
- Rice vinegar: gentler and slightly sweet (check that it is at least 5% acidity)
Sugar: One tablespoon adds just enough sweetness to balance the vinegar without making the onions taste like candy. Honey or maple syrup can be used, though they add their own flavor.
Salt: Use fine sea salt or kosher salt. Avoid iodized table salt if you can, since it may cloud the brine slightly, though it is safe to use.
Aromatics and spices: Garlic, peppercorns, mustard seeds, and red pepper flakes add depth. They are optional, but even a few peppercorns make the brine taste more complex.
Lime juice: A splash of fresh lime juice adds a bright citrus note that pairs beautifully with tacos and Latin-inspired dishes.
Instructions
Peel the red onions and slice them into thin rings or half-moons. For the most even results, use a sharp knife or a mandoline, aiming for slices about ⅛ inch (3 mm) thick. Separate the slices with your fingers so the brine can reach every layer. Uniform slices pickle evenly and stay crisp.
Pack the sliced onions into a clean, heat-safe glass jar. Add the garlic, black peppercorns, mustard seeds, and red pepper flakes if you are using them. A wide-mouth jar makes packing and serving easier.
In a small saucepan, combine the vinegar, water, sugar, and salt. Heat gently, stirring until the sugar and salt dissolve. Bring the mixture to a brief simmer, then remove it from the heat right away. There is no need to boil it for a long time, and overcooking the brine does not make the pickles any better.
Carefully pour the warm brine over the onions until they are fully covered. Gently press them down with a clean utensil to release trapped air bubbles and make sure every slice is submerged. Onions that stick out above the liquid will not pickle evenly.
Let the onions cool until they are no longer hot, then cover the jar and refrigerate promptly. Do not leave the jar sitting out for hours.
Chill for at least 30 minutes for a quick tangy bite. After 2 to 4 hours, the onions will be noticeably more flavorful and will turn a beautiful bright pink. For the best flavor, many cooks wait until the next day, when the brine has fully penetrated the onions.
Scoop out the onions with a clean fork or tongs and add them to tacos, burgers, sandwiches, salads, grain bowls, grilled meats, or your favorite snack boards.