Fermented Red Onions: A Beginner’s Guide

Fermented Foods and Drinks

Fermented vegetables like sauerkraut, kimchi, and pickles, have gained popularity in recent years for their numerous health benefits and unique flavors. But almost any type of vegetable can be fermented. While popular ones often steal the spotlight, there is another fermented delicacy that deserves equal attention – fermented red onions.

These tangy and slightly sweet condiments not only add a burst of flavor to any dish but also offer a host of probiotic advantages that promote gut health. Best of all, they’re incredibly easy to make. The beginner’s recipe below is a great basic recipe to get started.

fermented red onions in jar

But first, let’s understand the difference between fermented onions and pickled onions because the latter is much more popular and the terms are often confused.

Fermented Onions vs. Pickled Onions

The word pickling is often used interchangeably with the word fermenting but for the most part, pickling refers to preserving foods in an acidic medium at a high temperature (often in a water bath) which destroys the enzymes and probiotics. This method is sometimes referred to as chemical pickling. There’s also a very quick type of pickling which is a simple method to marinate and flavor vegetables in vinegar and sugar for 20 to 30 minutes.

Lacto-fermentation is a natural preservation process that uses just salt and water (and sometimes a starter culture like whey). The salt creates an environment that both encourages the growth of good bacteria (probiotics) and prevents the growth of bad bacteria. The naturally-occurring good bacteria break down and convert the starches and sugars in vegetables, (as well as fruits and dairy) into lactic acid (thus, the “lacto” of lacto-fermentation) which creates the sour flavor and acts as a preservative. This method is sometimes called fermentation pickling.

Most food companies prefer chemical pickling with heat and vinegar because this method allows for a more uniform product with an ultra-long shelf life.

However, preserving foods through fermentation is completely different than preserving foods through heat and vinegar. In particular, the high heat and vinegar involved in chemical pickling destroys the probiotics, enzymes, and nutrients. The complete opposite occurs via fermentation.

Health Benefits of Fermented Red Onions

fermented red onions
  • Source of natural probiotics. These beneficial bacteria are known to promote good gut health.
  • Enhances digestion. The beneficial bacteria break down (and therefore pre-digest) the sugar and starches for easier digestion and the increased enzyme activity also helps improve nutrient absorption.
  • Boosts nutrients. During the process of fermentation, some vitamins are manufactured such as B vitamins and vitamin K.
  • Potential immune system boosting properties through improved gut flora.

These benefits are really just the tip of the iceberg! Science is discovering more and more benefits of fermented foods and how gut flora impacts our health.

More Fermented Vegetable Recipes to Try

Taste Benefits of Fermented Red Onions

In my opinion, this is the biggest benefit of all. Fermented red onions are absolutely delicious! Pickled onions can be overly sour due to the vinegar and can really make your mouth pucker. They can also be overly sweetened with the addition of sugar. And raw onions, as you probably know, can be overly pungent and sharp.

However, the process of fermentation softens the flavor of raw onions and creates much more complex flavors.

After fermenting, red onions have a very fresh, pleasantly sour and slightly sweet flavor. Neither the sour nor sweet flavor is overpowering. It’s a delicate tangy taste that makes a great addition to many dishes!

Uses for Fermented Red Onions

There are almost unlimited uses for fermented red onions. Simply substitute them anywhere you’d use raw or even cooked red onions. Here are just a few ideas:

  • Topping for burgers and sandwiches
  • Topping for tacos and nachos
  • Topping for pizza
  • Topping for salads
  • Addition to egg dishes like scrambled eggs or omelets

How to Make Fermented Red Onions

It’s so unbelievably easy! All you need are some glass jars, red onions, salt, and water.

Step 1. Prepare the onions. Peel and then cut off the ends of the onions. Cut each onion in half and then thinly slice them.

Step 2. Prepare the salt water brine. Dissolve 1 tablespoon of salt into 12 ounces of filtered water.

Step 3. Pack and pour. Pack the red onions into a 12-ounce glass mason jar. Pour the brine over the onions. Leave one inch between the top of the jar and the top of the brine. Use a fermentation weight (find a good source for fermenting weights here) to keep the onions under the salt brine, if necessary.

Step 4. Ferment! Leave the jar in a cool, dry place at room temperature for five to seven days. Use an airlock fermentation lid (find a good source for airlock lids here) or burp the jars (meaning just open them) every day to let out the gasses that are a natural byproduct of fermentation. If the water level rises, simply pour some out.

Taste after five days. They should have a pleasantly sour flavor. If it’s not developed enough, let it ferment for another day or two. You can go even longer if you prefer. The taste will continue to change over time.

Step 5. Transfer to the fridge When you’re happy with the taste, transfer the onions to the fridge. They will continue to ferment albeit at a much slower pace and will last for many months in your refrigerator.

Printable Recipe

fermented red onions

Fermented Red Onions

Red onions, water, and salt are all it takes to make lacto-fermented red onions. They're easy to make, tasty, and healthy.
Print Recipe Pin Recipe
CourseSide Dish
Prep Time15 minutes
Total Time15 minutes
Servings12 ounces
AuthorCraig Fear


  • 2 medium red onions peeled and thinly sliced into rings
  • 1 TBSP sea salt
  • 12 ounces water filtered


  • Pack sliced onions firmly into 12 ounce glass jar. 
  • Dissolve salt in 12 ounces of filtered water to create a brine.
  • Pour the brine over onions and tilt jar a few times to mix well.  Leave one inch between the top of the jar and the top of the brine. Use a weight to keep the onions under the brine, if necessary.
  • Let sit on counter for five to seven days. Use an airlock lid or burp the jars (meaning just open them) every day to let out the gasses that are a natural byproduct of fermentation.  If the water level rises, simply pour some out.
  • Transfer to the fridge.


Serving: 12ounces | Calories: 7kcal | Carbohydrates: 2g | Protein: 0.2g | Fat: 0.02g | Saturated Fat: 0.01g | Polyunsaturated Fat: 0.003g | Monounsaturated Fat: 0.003g | Sodium: 293mg | Potassium: 27mg | Fiber: 0.3g | Sugar: 1g | Vitamin A: 0.4IU | Vitamin C: 1mg | Calcium: 5mg | Iron: 0.04mg

Lacto-fermented red onions are not as commonly made as pickled red onions but they're easier to make, tastier and healthier! Learn how here!
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Fermented Red Onions: A Beginner\'s Guide

About the Author

Craig Fear is the creator of Fearless Eating and the author of three books, The 30-Day Heartburn Solution, Fearless Broths and Soups and The Thai Soup Secret. After years helping clients with digestive issues, Craig decided to pursue writing full-time. He intends to write many more books on broths and soups from around the world! Click here to learn more about Craig.

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