I finally managed to nail the flavor profiles for my pickled onions after several attempts over several years. I didn't write down the exact measurements. It's a simple brine of cider vinegar, fresh lime juice, water, salt, sugar, halved serrano peppers and of course the red onions.
We put pickled onions on almost every dish we make at home, from quesadillas to shrimp to green salads and as a condiment with pate' or ham on a cold plate. When I ran out of the first batch of onions, I disposed of the serranos, then simply added more red onions and fresh serranos to the existing leftover pickling liquid.
I've been doing this for well over a month. Nothing looks or smells funky from batch to batch; I'd guess I'm on my 5th batch??
Is it safe to do this ad infinitum as long as there are no tell-tale signs of spoilage?