Thinly slice the red onion to your desired thickness using a knife or mandolin.
Add the cut onions to your jar
Add in the apple cider vinegar, warm water (but not boiling!), salt, and maple syrup into your jar and give it a good mix. Don’t worry if the mixture doesn’t cover all the onions at first. As the onions soak in the vinegar mixture they’ll soften and shrink down, making it easier for the liquid to fully cover them.
Close the jar and put it in the fridge for a few hours until the onions and mixture are nice and pink. The time they need varies depending on how thick you slice your onions. I like to leave my mixture in the fridge overnight so the onions can really absorb the flavor.
There you have it! A quick, easy pickled red onion recipe.
Notes
If cutting onions makes your eyes water (because same), place a moist paper towel next to your cutting board. This helps to absorb some of the cry-inducing gas that onions release.
If the water is boiling it may cook the onions and make them less crispy. The water just needs to be warm enough to help the salt dissolve.
Don’t drain the liquid when the onions are ready. This mixture helps keep the onions full of flavor and preserved so they last longer.