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Easy Lacto-Fermented Onions Recipe

Lacto-fermented onions are seriously one of my all-time favorite ferments! For starters, they are delicious and smell amazing! Fermenting onions is a great way to keep onions on hand all the time (they last forever), and they are so, so, sooooo versatile!

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Lacto Fermented Onion Slices

I love to throw them in salads, on sandwiches, in Chipotle bowls store-bought or homemade, in fajitas, tacos… it would probably be easier to say what I don’t enjoy them with!

My son really loves fermented onions as well. He like to eat them alongside his eggs, with potatoes, in grain-free tacos (I finally found some great options for him!), and by themselves.

Let’s go ahead and learn how to ferment onions so you can enjoy them, too!

When you are fermenting onions, you have several choices. You can:

  • slice them
  • dice them
  • quarter them
  • ferment them whole

The sky is the limit.

Why make lacto-fermented onions?

Fermenting them whole is a great way to preserve for a year or more, or to decide what you want to do with them whenever the need arises. It’s also a great way to ferment pearl onions, which are small and already bite-sized.

For this fermented onion recipe, we will slice the onions thinly as if making sauerkraut.

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! The thin shreds it creates is perfect for making homemade sauerkraut and fermented onions.

I use these thin slices on everything. It’s amazing on a sourdough Tuna sandwich, amazing by itself, and amazing in salads!

Related Post: Fermenting Equipment I LOVE And Use Regularly

How long does it take to ferment onions?

Fermenting onions is super easy and quick if you slice them thinly. I usually give my thinly sliced onions 2 weeks to ferment (one week at room temp, and one week in the fridge), but shortening this time by about half is OK, and you can generally consume after a week.

Fermented Onion Rings

Easy Lacto-Fermented Onion Recipe
Fermenting onions is easy, quick, and makes the most perfect, thinly sliced condiment for salads, sandwiches, soups, etc.
Course Ferment


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


  • 2 lb onions (approximately 2 large onions)
  • 8 g salt


  • Peel onions and remove the ends.
  • Put mixing bowl on kitchen scale and zero it out.
  • Slice onions thinly and move to the mixing bowl. Using a mandolin will help create uniformly thin slices.
  • Note measurement of sliced 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.
  • Add salt (approximately 8g or 1.5 tsp) and mix well.
  • Move onions to jar, pressing down 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

This is a fermenting recipe I highly recommend you try. It is probably one of the easiest ferments to make, so it’s a great ferment recipe for absolute beginners.

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.

These lacto-fermented onions make the perfect condiment. Once you’ve tried them, let me know if you agree!

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Friday 21st of May 2021

WOW just tasted the onion ferment and it is great. Made it in my Mad Millie Crock as per your recipe and it is a hit.


Wednesday 26th of May 2021

I am so glad you enjoy it! It is definitely one of my favorites and is an easy one to make!


Wednesday 19th of May 2021

Hi, I am wondering if we need to add water to cover the onion?


Monday 8th of November 2021

@Jer, It's important the the onions are under the brine. If they don't release enough liquid, you can add brine to cover, 1/2 tsp salt to a cup of water.


Wednesday 19th of May 2021

Hey there! If you thinly slice the onions then there is no need to add water. It will create it's own brine.

If you cut in quarters or chunks then you would cover with a 2% brine.

Naturally Fermented Red Onions | Nourishing Time

Tuesday 27th of October 2020

[…] 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 […]