How to Make Lacto-Fermented Onions – Easy Recipe!

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Learn how to make lacto-fermented onions at home. Not only are fermented onions simple to make, but they also offer a heaping dose of probiotic health benefits. Mild in flavor and big in nutrition, they are delicious in a salad, on a burger, or as a side.

If you’ve been following my blog or YouTube channel for any length of time, you are probably sick of hearing me talk about lacto-fermented bell peppers. They are, hands down, one of my favorite foods.

Lately though, I’m obsessed with fermented onions. I don’t know if that’s good news or bad news because now you’ll hear me incessantly talk about both fermented onions and peppers. But I can’t help myself. They are just so good.

It all started this spring when I scored a few strawberry onions from a local farmers market. They were giant, and I was worried we wouldn’t get through them in time. So I decided to preserve them via fermentation.

And the rest was history. We could not stop eating them.

They are crunchy with a mild flavor and a touch of tang and salt. We piled them on pizzas, salads, burgers, and nachos. You name it, we put fermented onions on it.

Like freeze-dried foods such as strawberries and herbs, fermented onions have become a staple ingredient in our home.

To make fermented onions, all you have to do is combine a few basic ingredients: sliced onions, salt, and water. Really, that’s it.

Yet, somehow, the end result is so delicious and nutrient-dense that it doesn’t seem possible that it’s literally onions, salt, and water.

So if you feel intimidated by fermenting onions (or any veggie), don’t sweat it. If you can mix salt and water together (and I know you can), you can 100% ferment onions at home.

Why You’ll Love Lacto-Fermented Onions

Simple and Delicious

Fermentation is a great way to preserve onions (or any veggie), and unlike other forms of food preservation, it’s a simple process. In my opinion, it’s the only food preservation method that improves the food’s flavor. During the fermentation process, the onions become mild and tangy, yet they stay crunchy.

Small-Batch Food Preservation

I live on 1/8 acre and have a small suburban homestead garden. I can’t grow an endless supply of food. And even if I could, we don’t have a cellar or homestead pantry to store it. So lacto-fermentation is my favorite way to preserve food because it’s easy to do in small batches. And since it doesn’t last an eternity, you can use it up within a reasonable amount of time to open up pantry/fridge space.

Probiotic Nutrition

Store-bought fermented foods often contain little to no probiotic health benefits because they have to be pasteurized for shelf stability. Homemade lacto-fermented foods, on the other hand, are chock full of probiotics that are good for your gut health.

When you ferment onions at home, you cultivate all of the healthy lactic acid and beneficial bacteria that are often destroyed when store-bought fermented foods are pasteurized. Of course, this doesn’t suggest that pasteurization isn’t an important process. But it does change the food’s microbiome.

Plus, fermented onions are not readily available in stores. So by fermenting onions, you can elevate the flavors and ingredients in your day-to-day meals.

Tips for Fermenting Onions

• Submerge the onions in the brine – To prevent unwanted bacteria and mold growth, keep the onions completely submerged in the brine.
• Keep an eye out for mold – I’ve never had mold growth on any of my fermented foods. However, it can happen, so it is important to keep an eye out for any signs of mold. This usually happens if the food isn’t under the brine. If you see mold, unfortunately, you will need to toss the onions.
• Use your senses – Your senses are the best gauge. Notice what the onions look, smell, and taste like. Look to make sure there no signs of mold. And take a whiff to make sure they smell okay (they should smell tangy and onion-y). If they look and smell good, give one a taste test to see if it is fermented to your liking.
• Use a fermentation weight and lid – I’ve seen a lot of fermentation weight and lid hacks. And though they all work, I’ve found that the easiest way to ferment onions is to use a glass fermentation weight and a self-burping lid.
• Cloudy brine is normal – Don’t panic if the brine gets cloudy. It’s a natural part of the fermentation process.

How to Use Lacto-Fermented Onions

You can use lacto-fermented onions as you would fresh onions. However, if you cook fermented onions, they will lose their probiotic nutrition. Probiotics can survive warm-ish temperatures. But at around 120° F, they will begin to die.

This isn’t a deal breaker. It’s still perfectly useable and delicious food. After all, part of the point of fermenting onions is to preserve them for later use, including cooking. But it does mean that the nutritional quality will change.

You can use them raw or cooked for just about anything. And if you don’t like the taste of raw onions, you might like fermented ones better because they are milder.

These are my family’s favorite ways to use them:

• Burgers – A smash burger on a sourdough bun with fermented onions is everything!
• Salads – I love fermented onions paired with blue cheese dressing.
• Avocado Toast – Toasted sourdough smothered in mashed avocado and fermented onions is great for breakfast, lunch, or a snack.
• Nachos – Top crispy chips with cheese, salsa, black olives, and fermented onions
• Onion Relish – Chop up the lacto-fermented onions and add a dash of sugar for a probiotic-rich onion relish.

Tools You Will Need for Fermenting Onions

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• Mason jar – You will need to pack the onions in the jar tightly. So make sure you have the correct size jar. For two large onions, I used a quart-sized mason jar.
• Fermentation lid – Masontops Pickle Pipes are my favorite because you don’t need to worry about burping the jar. You can use a regular canning lid and ring. But you will have to burp it daily to release the pressure.
• Fermentation weights – I like to use a pickle pebble to hold the onions under the salt water brine. However, I’ve also used a small silicone funnel, which worked well.
• Measuring spoon – Grab a tablespoon to measure the salt.
• Knife – You will need a sharp knife to slice the onions.
• Cutting board – Any cutting board will do the job. I prefer an end-grain cutting board for most kitchen projects.
• Bowl or large measuring cup – I like to use a Pyrex measuring cup or anything with a pour spout.
• Whisk or spoon – Use a whisk or spoon to stir the salt and water.
• Food-safe funnel – If you are like me and make a huge mess every time your pour water, a funnel can help prevent spilling all over the counter.

Ingredients

• Sliced Onions – Cut the onions into thin slices. Make sure they are fresh and free of any blemishes, bruises, or rotten spots. The number of onions will depend on their size, how you slice them, and how tightly you pack them.
• Salt – Generally, I recommend steering clear of table salt or ionized salt for fermenting and other forms of food preservation. For best results, I prefer to use canning salt, sea salt, or kosher salt.
• Water – Here on the North Carolina coast, our tap water is really gross. So I use filtered water for fermenting. But tap water generally is okay to use. If you aren’t sure, I recommend filtering it first.

How to Make Lacto-Fermented Onions

1. In a large bowl or glass measuring cup, combine the salt and water. Stir until the salt is completely dissolved. Set aside.
2. Pack the onion slices into a clean jar. I usually use the handle of a wooden spoon to press them down.
3. Pour the brine over the onions, leaving about an inch of headspace. Use a spoon to press the onions, ensuring they are tightly packed. If you find there is more room in the jar, add more onions. Often, the onions will settle after a few minutes, and you can add more.
4. Place a weight on the onions, making sure they are completely under the salt brine. If any pieces float to the top, either remove them or reposition the weight so they are under the brine.
5. Put a fermentation lid on the top of the jar (follow the manufacturer’s instructions for your fermentation lid).
6. Let the onions ferment at room temperature out of direct sunlight for about 5-7 days. Around day 5, taste test an onion to see if it is fermented to your liking. If so, swap out the fermentation lid for a regular lid and store in the fridge. If they need more time, continue fermenting and check daily until they have reached your desired flavor.

How to Store

Store your finished onions in the fridge for 3-5 months. Be sure to replace the fermentation lid with a regular lid before storing in the refrigerator. I usually use a reusable plastic lid (affiliate link).

Frequently Asked Questions

What Types of Onions Can You Use?

My favorites are red onions, strawberry onions, and yellow onions. However, you can ferment any type of onion, including pearl onions. So use what’s available and what you have on hand.

Is This the Same as Quick-Pickled Onions?

No, pickling and fermenting are different processes. Pickling uses white vinegar, apple cider vinegar, or other acidic brine to create a sour flavor and preserve food. Fermenting, on the other hand, does not use acid.

But just to keep you on your toes both pickled and fermented foods are often called “pickles.” Le sigh.

Should I Use Hot or Cold Water?

Cold or room temperature water is best. Hot water can kill the bacteria on the onion’s surface, which is needed for fermentation. So if you need to heat your water for any reason, make sure you let it cool to room temperature before pouring it over the onions.

How Much Salt Should I Use for Fermenting Onions?

Often, fermenting recipes call for grams of salt rather than measurements. This is technically a more precise way of determining the salt. But since onions need a 2%-5% salt brine, there is some flexibility.

The more salt, the faster the onions will ferment. And, of course, the saltier they will taste.

Through my testing, I’ve found that 2 tablespoons of salt per 2 cups of water encourages an optimal fermentation rate and balanced flavor.

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