Pickled onion cider instead of pickled onions

I have been making pickled onions for years with no problems. I have recently bought pre peeled onions and find that in the pickle, these onions fizz in the jar.
Why is this - the onions look fresh and healthy?
Best Answer
The situation you describe sounds like natural Lacto-fermentation.
There are many airborne yeast around us all the time. Every culture on earth (no pun intended) has a some tradition of fermentation for storage purposes. It would seem that you have just the right conditions for that to occur.
This can be a good thing. It creates a product with properties than many find healthful. A few resources are here:
Same principle for white onions. If you submerged the onion goodness you have going on with a clean disc of some sort you can finish the fermentation and have a yummy condiment !
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What is the difference between pickled onions and pickled shallots?
First of all, unlike regular onions, which grow as single bulbs, shallots grow in clusters, more like garlic. They are a bit sweeter than regular onions, and their flavor is more subtle.What is the difference between pickling onions and onions?
Pickled Onions or Shallots Select firm, bite\u2010sized onions or shallots to make pickle \u2013 don't make the mistake of using up your floppiest specimens. Onions that are labelled as pickling onions will be sweeter and milder than the full\u2010strength varieties.Can I reuse pickling liquid for onions?
Reuse the liquid: After your first batch is all used up, you can reuse the pickling liquid up to 4 times. Adjust the vinegar, salt and add some hot water to the next batch.What is another name for pickled onions?
Pickled onion There is a variety of small white pickled onions known as 'silverskin' onions, frequently used as an essential component of the Martini cocktail variant known as a Gibson. Pickled onions are usually pickled in malt vinegar and the onions are about an inch in diameter.How to Make Homemade Pickled Red Onions | SAM THE COOKING GUY
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Answer 2
What you describe is "fermentation" and what you have accidentally created is indeed onion cider. ;-)
It'll be very hard to deduce the exact root cause for this particular batch with the information we have but maybe:
- you baked bread while pickling your onions and one speck of yeast was caught in your brine after it was boiled.
- the onions were stored near a broken pack of dry yeast in the shop and not washed/sterilized thoroughly before being put in their jars
- one speck of yeast landed in just one jar as the window was open while you were cooling down the jars with their lids off and all the others are fine.
- ...
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