For the original recipe and instructions, see: "Pickled Red Onions" at foodfidelity.com
These will last for a few months, but of course they start to lose their flavor and crispness after a while, so I prefer to finish them in 1-2 weeks.
Only use glass or ceramic containers. Avoid metal which can react with the vinegar. Plastic is troublesome to given it absorbs flavors.
Whole spice seeds (peppercorns, pepper flakes, fennel seeds, etc.) are good ways to spice things up. Bay leaves add something as well
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