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Naturally Fermented Red Onions

I previously shared a simple recipe for making fermented onions. Because they are seriously one of my favorite ferments, today I want to share how I make naturally fermented red onions with you!

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Naturally Fermented Red Onions

Just as with the previous recipe I shared, you are welcome to cut your onions however you like. I tend to shred them, but you have several options. You can slice them, dice them, quarter them, or even ferment them whole if they will fit in your fermenting vessel!

Please note that if you make larger cuts, you will need to cover the onions with a brine. To make a 2% brine, which is perfect for your onions, you simply mix 5 grams of salt per cup of water.

I usually slice mine thinly because I love to just take a couple forkfuls out and throw in this or that without further prep.

For thin slices, I love to use the smaller side of this mandoline. I’ve had this mandoline for around 7 or 8 years and still love it as much as the day it arrived! I know I say this in almost every recipe I share on here, but I’m not kidding! The thin shreds it creates is perfect for several recipes that I make, including this lacto-fermented red onions recipe!

Fermented Red Onions

I use these thin slices on everything. It’s amazing on a sourdough Tuna sandwich, in salads, fajitas, tacos, soups, stews…. seriously it’s good with everything!

Related Post: Fermenting Equipment I LOVE And Use Regularly

Note that the recipe below contains beets. This is for color as the beautiful red color of the onions lightens quite a bit. I love that deep red color, so I just add a few chunks or slices of beets at the bottom of the jar before putting the onions. The beets taste amazing, or you can toss ’em. But seriously, they taste amazing!

Without further ado, here’s how to ferment red onions!

Naturally Fermented Red Onions

Fermented Red Onion Recipe
Fermenting red onions is easy, quick, and makes the most perfect, thinly sliced condiment for salads, sandwiches, soups, etc. It takes a little longer than quick pickled onions, but the short wait is SOOOO worth it!
Course Ferment


  • Mandoline or knife
  • 1 L jar
  • Airlock lid (I use Pickl-It) recommended
  • mixing bowl
  • Kitchen scale


  • 2 lb red onions approximately 2 large onions
  • 8 g salt
  • 1/4 small beet (optional, for color)


  • Peel the red onions and remove the ends.
  • Put mixing bowl on kitchen scale and zero it out.
  • Slice red onions thinly and move to the mixing bowl. Using a mandoline will help create uniformly thin slices.
  • Note the weight of the sliced red onions in mixing bowl. It should be around 1.5lbs. If you have more than this, remove the extra. You can use the rest in dinner, a salad or refrigerate/freeze for future use.
  • At this point you can slice the beets and put at the bottom of your fermenting jar OR shred and add to the onions.
  • Add salt (approximately 8g or 1.5 tsp) and mix well.
  • Move red onions to your fermenting jar, pressing down gently as you go along. Make sure your jar is clean and you don't fill past the shoulder. Onions tend to create plenty of juice so making the cut off the shoulder or a little below is pretty wise!
  • Let ferment for one week at room temperature, and one week in the fridge. This is a ferment you will want to put on something to catch excess liquid just in case it leaks!
  • Enjoy!!!
Keyword Onions

Using weights is optional for the slices, but if you are new to fermenting you may want to go ahead and weigh them down. I find that within a day or two there’s plenty of brine to completely cover the onions.

You can begin eating after the initial week of fermentation if you want/need to! But I find giving it two weeks is even better!

These fermented red onions are the bomb! Let me know if this is now one of your favorites as well!

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Sunday 23rd of July 2023

Fabulous recipe! Bought several more fermenting jars to make lots????

Easy Lacto-Fermented Onions Recipe - Nourishing Time

Thursday 30th of June 2022

[…] If you’ve tried onions in all its forms, then you know that the taste of raw onions can be quite spicy. When you ferment onions, it eliminates the harsh bite you can experience from onions. In my opinion, fermentation is the most delicious way to prepare onions! I even have a fermented red onion recipe! […]