Peel and thinly slice the red onions into half-moon shapes.
In a non-reactive bowl or measuring cup, combine the red wine vinegar, salt, and sugar. Stir until the salt and sugar are fully dissolved.
Place the sliced red onions in an airtight container. A glass jar or plastic container with a tight-fitting lid works well.
Pour the prepared pickling liquid over the red onions in the container, ensuring that the onions are fully submerged.
Seal the container with its lid or cover it tightly with plastic wrap. Place the container in the refrigerator.
Allow the onions to marinate in the refrigerator for about 1-2 hours or longer for a stronger flavor. The longer they marinate, the more pronounced the pickled flavor will be.
Your pickled red onions are now ready to use as a delicious condiment or topping for various dishes.
Notes
Thinly slicing the onions into half-moons ensures they pickle evenly and absorb the vinegar mixture well.
It's important to use a non-reactive bowl (like glass or ceramic) for mixing the pickling liquid to prevent any chemical reaction with the vinegar.
The combination of red wine vinegar, salt, and sugar creates a balanced pickling liquid. Adjust the quantities slightly according to your taste preference.
Ensure that the salt and sugar are completely dissolved in the vinegar for a consistent flavor throughout the pickling liquid.
The onions should be fully submerged in the pickling liquid for even pickling. You can add a bit of water if there's not enough liquid to cover the onions.
Pickled red onions are versatile and can be used to enhance many dishes. They can be stored in the refrigerator for several weeks.