Fermented onions are made using brine (water and salt) and time. Fermenting onions at home is easy and totally worth the effort. The best part is that the health benefits are enormous! Fermented onions are more digestible and higher in nutrients than raw, fresh onions. Fermented vegetables are rich in enzymes and probiotics.
Although there are many health reasons to incorporate fermented foods into your kitchen, many people choose to ferment foods for the delicious flavour. Fermenting onions makes them less pungent but creates a fresh, tangy and sour condiment that is perfect for topping dishes such as stir-fries or salads. I love having fermented onions or fermented leeks in my fridge to add an extra boost of nutrition to my lunch bowls.
It took me a long time to work up the courage to try lacto-fermenting vegetables in my home kitchen. I was convinced of the health benefits and it was painful spending so much of my grocery budget on expensive jars of fermented vegetables from the health food store when I knew I could do it for a fraction of the cost at home. But I was nervous that I wouldn’t know if the fermentation had gone wrong.
After a lot of reading, experimentation and watching videos including this one by Joshua Weissman, I now feel super confident when fermenting vegetables. Here are some of my tips for a successful fermentation.
Tips for Successful Fermentation
- Use a kitchen scale. This method ensures that you’re using enough salt and increases the chance of a successful fermentation.
- Keep the onions totally submerged. It’s important that the item you’re fermenting is kept in an oxygen free environment. Peek at your fermenting jar once a day to check that everything is still submerged.
- Discard your ferment if you see black or brightly coloured molds.
- Discard your ferment if it smells really awful. If you’re not sure what I mean by this, believe me you’ll know.
- Keep your ferments out of direct sunlight.
Ways To Use Fermented Onions
- Top burgers or sausage.
- Mix into a Greek salad.
- Use as a condiment to add acidity and brightness to a dish.
- Add colour and nutrition to your plate.
- Top scrambled eggs or an omelette.
How to Ferment Onions
- Choose a mason jar that is the appropriate size to fit the sliced onion. I used a 16 oz wide mouth style mason jar. Place the mason jar on your kitchen scale and press tare to zero out the weight of the jar.
- Fit the sliced onion into the mason jar and pour in enough water to cover the onions. Take note of the total weight in grams of the onion and water combined. To determine the amount of salt you need to add in grams, multiply that number by .02.
- For example If the weight of the onion and water combined is 800 grams then you will multiply 800 by .02 and get 16. I would add 16 grams of salt to my jar.
- Tare the scale again and add the amount of salt in grams that you determined in the above step. Put on the lid and shake well to dissolve the salt.
- It’s very important to keep the onions submerged. To do this you can use fermentation weights, pinch bowls, small mason jar or a plastic sandwich bag filled with a little water. (See photos for examples.)
- Leave your ferment at room temperature away from sunlight for 4-7 days. Check it once a day to make sure the onions are submerged. Open the lid slightly on a daily basis to prevent pressure from building up in the jar. Close it again tightly.
- Once your fermented onions have reached the desired flavour, place the jar in the fridge. This will halt the fermentation process. Your fermented onions will now keep for a very long time. Enjoy!
Frequently Asked Questions
What is lacto-fermentation?
Lacto-fermentation is the process of lactic-acid-producing bacteria breaking down the sugars or glucose in fruits, vegetables, or other foods into lactic acid. It does this in an environment free of oxygen.
You can lacto-ferment many different vegetables or foods including meat or dairy. Some examples of popular lacto-fermented foods would be yogurt, sourdough bread, sauerkraut and cucumbers.
Does lacto fermentation produce alcohol?
Yes, lacto fermentation can produce trace amounts of alcohol. This happens as the bacteria breaks sugar down into lactic acid. Typically the alcohol content is very minute but the longer a ferment is left out at room temperature, the more risk for the alcohol content to increase.
What salt is best for lacto fermentation?
The best salt to use for lacto fermentation would be either unrefined sea salt or pickling salt. Avoid using an iodized salt like table salt or a heavily refined salt as this can affect your ferment.
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Tools You May Need For This Recipe
Kitchen Scale
Mason Jar
Fermentation Weights
Pickling Salt
Noma Guide to Fermentation
Fermented Onions
Lacto Fermented Onions
Equipment
- kitchen scale
- fermentation weight or plastic sandwich bag
- mason jar (16oz)
Ingredients
- 1 large onion
- distilled water weight to be determined
- sea salt or pickling salt weight to be determined
Instructions
- Choose a mason jar that is the appropriate size to fit the sliced onion. I used a 16 oz wide mouth style mason jar. Place the mason jar on your kitchen scale and press tare to zero out the weight of the jar.
- Fit the sliced onion into the mason jar and pour in enough water to cover the onions. Take note of the total weight in grams of the onion and water combined. To determine the amount of salt you need to add in grams, multiply that number by .02.
- For example If the weight of the onion and water combined is 800 grams then you will multiply 800 by .02 and get 16. I would add 16 grams of salt to my jar.
- Tare the scale again and add the amount of salt in grams that you determined in the above step. Put on the lid and shake well to dissolve the salt.
- It’s very important to keep the onions submerged. To do this you can use fermentation weights, pinch bowls, small mason jar or a plastic sandwich bag filled with a little water. (See photos for examples.)
- Leave your ferment at room temperature away from sunlight for 4-7 days. Check it once a day to make sure the onions are submerged. Open the lid slightly on a daily basis to prevent pressure from building up in the jar. Close it again tightly.
- Once your fermented onions have reached the desired flavour, place the jar in the fridge. This will halt the fermentation process. Your fermented onions will now keep for a very long time. Enjoy!
Notes
Nutrition
If you make this recipe please leave a comment and give this recipe a rating! I aim to respond to every single comment. I am so grateful when you trust me and try one of my recipe creations in your own kitchen. I love to hear how it went! Let’s connect on Instagram and tag me in your food pics!
‘Til next time,
Christy
Redeemed Acres says
I want to encourage people to not use plastic bags or Tupperware with onions especially as onions are a naturally puller. They will suck up all the micro plastics and that's what you will be eating. Then you can look into micro plastics effects on your body and health. Remember healthy foods are only as healthy as the quality of foods and tools you use. Mason fermenting kits are the best the weights are made out of the same glass as their jars. They will last forever, super affordable, and easy to use and reuse over and over.
Shaima Wahab says
No, that's only necessary for the process. After that, just leave it in the fridge in an airtight container, and it'll last for months. I'm not even kidding, I had a little leftover that I transferred to a small plastic container, so I could use the jar for the new batch, and I forgot about the leftovers for months. When I realized they were still sitting there like six months later, I tasted it and it was still perfectly fine.
Jennifer says
I'm trying to eat more fermented foods and learn to like them better. Last month I found this recipe and fermented them the full 7 days, these are now my favorite fermented food! My kids Even eat them on everything!
Mike says
Hello, does it have to be distilled water? Is it better for the fermenting process?
Thanks
Mike
Christy Faber says
Some people have found tap water to negatively effect the fermentation process so I've always found it safest to just use distilled water so I don't waste any ingredients. 🙂
Bob says
I always boil the water in advance - it boils off the Chlorine added to our tap water.
Next, I let it boil for a little bit to be sure. Then I let it cool to room temp.
Last, I use it in my Ferments.
Anna Pedret-Dunn says
Followed the recipe which was very easy, except I left my jar on the kitchen counter in day light (but not in direct sun light) for the first 24h, but should it be stored somewhere dark, ideally? I have put it in the cupboard now though it might be a little late.
Looking forward to trying result in any case.
Beck says
Is there a way to make this shelf-stable vs fridge stored?
Christy Faber says
If kept on the counter the onions will continue to ferment so they will get tangier and tangier and even a little effervescent. Storing them in the fridge will halt the fermentation and keep them stable for months. Hope this helps!
Chris says
Hi, I was wondering if once placed in the fridge after the initial fermentation at room temperature, is it still critical to use weights to maintain an anaerobic environment in the fridge? Or once in the fridge is it okay not to use weights and vegetables aren't fully submerged anymore without as much of an anaerobic environment? Thank you!
Hayley Dhanecha says
I have many onions in my pantry that are almost impossible to finish in my cooking, will ferment some of them using your recipe. thnaks for all the tips!
Jenny says
This is very informative; I enjoyed reading your post. We have tried pickled onions but never fermented onions. I am curious to try this, it looks doable and I am curious about their taste. Thank you.
silvia says
I usually pickled my onions, but I've been researching about fermenting them. You have given me a lot of great tips and something to think about. I'm just waiting to get my onions from my home garden and I'll get to work!
Dee says
I think I'll start pickling my onions like this. I normally just throw them in the fridge submerged in vinegar without any rhyme or reason. Thanks for the great tips.
Carrie Robinson says
I have never heard of this process before, but now I am totally intrigued! 🙂 The healthy benefits sound absolutely amazing.
Veronika says
I love making my own fermented food! Never tried it with onions and cannot wait to make this recipe this weekend 😉
Leslie says
You have had the exact concerns I have had when contemplating whether or not to ferment vegetables on my own. I appreciate this post more than you know!
Sean says
Such a great way to get your probiotics and I love sauerkraut. How long can I keep them. Are they still good after about a month?
Bernice says
I make sauerkraut quite often and have tried fermenting pickles. The kids didn't like the difference in flavour from their regular dills. I never even thought about fermenting onions! I'm very curious and I think they would be great in so many dishes.
Gloria says
We love sauerkraut, so I find this recipe very interesting. I always have pickled onions in the fridge. This will be a nice alternative for sure.