How to Ferment Vegetables (Lacto-Fermentation)

Would you like to learn or perfect the art of lacto-fermentation?

This guide will give you the basics you need to ferment any vegetable at home!

Go straight to the section that interests you, or read on:

What Is Lacto-Fermentation?

Lacto-fermentation is a fermentation process driven by lactic acid bacteria, which convert sugar into lactic acid. Despite its name, the term “lacto” has nothing to do with milk or lactose.


The terms “lactic acid fermentation” and “lacto-fermentation” are synonyms that describe fermentation using lactic acid bacteria.

In Everyday Language

In everyday language, lacto-fermentation is often known as salt-based vegetable fermentation. However, the term actually has a much broader meaning.

Lacto-Fermentation Uses

Lacto-fermentation is a common technique for preserving various foods. Some of the best-known lactic acid fermentations include:

For this article, we’ll focus solely on vegetable fermentation.

Ready to get started right away? Check out our 3 Foolproof Fermented Vegetable Recipes and get one of our lacto-fermentation kits!

Want to get started right away? Here are our most popular lacto-fermented vegetable recipes:

But if you’re the type who wants to know everything, then read on… You won’t be disappointed!

Summary of a Lacto-Fermentation Recipe

All fermented vegetable recipes boil down to this simple formula: Vegetables + Salt – Oxygen

Lacto-fermentation process

The classic steps in a lacto-fermentation recipe are as follows:

  1. Cut up the vegetables.
  2. Add the salt. You can add the salt directly to the vegetables and let them soak (dry salting), or you can make a brine. These methods are described in detail in the section “Methods for adding salt“.
  3. Put the vegetables in containers and limit their contact with oxygen. This creates a favourable environment for good bacteria (lactic acid bacteria) and prevents the proliferation of undesirable microorganisms.
  4. Leave to ferment on the counter. Wait and let the magic of fermentation happen!
  5. Enjoy! You’ll end up with tasty, healthy vegetables that can be safely stored for a long time.

Don’t hesitate to experiment with the different types of vegetables available to you. Lacto-fermentation is much simpler than it looks! The many benefits of lacto-fermentation are at your fingertips.

Lacto-Fermentation Ingredients

Cutting fermented vegetables

To prepare a lacto-fermentation, you’ll need the following basic ingredients:

  1. Vegetables: All vegetables (and even fruit) can be lacto-fermented! The key is that they must be edible raw. You can rinse your vegetables under running water but remember that their skins contain the lactic acid bacteria needed for fermentation. Cabbage, carrots, beetroot, and cucumbers are the most popular vegetables to start with.
  2. Bacteria: The lactic acid bacteria needed for fermentation are naturally present on vegetables. If you want to add lactic acid bacteria to ensure successful fermentation or to control it more effectively, you can add Caldwell’s Vegetable Starter Culture. Another option would be to add liquid from one of your previous lacto-fermentations but avoid this method for cucumbers as it could make them mushy.
  3. Salt: Salt is crucial for fermenting vegetables. It encourages the development of good bacteria and preserves the texture of vegetables. When choosing your salt, make sure its only ingredient is “salt” and that it’s free from iodine and anticaking agents. 👉 For more details, see the article Best Salt for Fermenting Vegetables.
  4. Water: Water is only used if you are preparing vegetables in brine. If your water is chlorinated, let it stand for about 30 minutes in a jar before adding it to the vegetables. 👉 To find out more, read: Which is The Best Water for Fermenting.

Jar of daikon kimchi

How to Achieve Successful Lacto-Fermentations

Choosing the Right Container

Several specific containers for lacto-fermentation allow you to meet the conditions necessary for good fermentation: letting the CO₂ out, limiting oxygen, and keeping the vegetables submerged.

Mason jar: Popular, accessible, and affordable container. However, over time, the metal lid will rust due to the acidity. Several fermentation accessories are designed for these types of jars.

“Le Parfait” type glass jar: These jars with lever lids and seals work very well. No need for special techniques to evacuate the CO2, as it will be able to escape on its own through the seal (change it if it lacks elasticity). However, avoid budget jars, whose quality is often disappointing!

Crazy Korean Cooking fermentation jar: All-in-one container with very good value for money. Its inner lid is very practical for limiting the presence of oxygen (and odours). Perfect for large recipes.

Ceramic jar: Traditional method. The jar comes with a weight and is sometimes fitted with a lid with a water gutter (airlock effect). Its two disadvantages: it’s expensive and fragile.

Vacuum bag: Very practical for restaurants, small portions, or for testing. Guaranteed oxygen-free! However, it produces plastic waste.

👉 See How to Choose Your Lacto-Fermentation Supplies for more details.

Add 2% Salt

This proportion is ideal for most recipes. The weight of salt depends on the weight of the vegetables or the volume of the container. Several levels of salt are possible, but bear in mind that:

  • If there is not enough salt, the fermentation will be colonized by all sorts of undesirable microorganisms. You should never put in less than 1% salt.
  • The more salt there is, the slower the fermentation and the longer the vegetables will stay crunchy. However, if you put in too much, the fermentation will be inedible!
  • For lacto-fermented vegetables that you want to keep for longer than 6 months, a higher salt content might be useful (3 to 4%).

👉 For more details, see How Much Salt to Use for Fermenting Vegetables.

Salt Addition Methods

There are two ways of adding salt:

Dry salting (sauerkraut style)

Dry salting is used when the vegetables can release their own water after being finely chopped (cabbage, onions, etc.). The percentage of salt is applied to the weight of the vegetables. For example, for a 2% sauerkraut recipe, weigh your cabbage and add 2% salt to this weight. If you have 1000g of cabbage, you’ll need 20g of salt (1000 x 2%).

Dry salting cabbage

Brine (pickle style)

Brine is used when the vegetables cannot release their own water, for example, when you want to ferment whole vegetables (garlic) or chopped vegetables (carrots). The simplest, quickest, and most accurate way of calculating the amount of salt to add is according to the volume of the container. Here’s a little trick to make the calculations easier: 1 litre of water is equal to 1 kg (1000 g) of water. For example, to make carrots with 2.5% salt in a 1 litre jar, you’ll need to add 25g of salt (1000ml x 2.5% = 25g).

Fermented carrots in brine

Some recipes produce a separate brine. This method is generally not recommended, as it can result in a final product that is far too salty. In this technique, a higher percentage of salt must be used (usually 3 or 4%), as the vegetables are not taken into account in the calculation.

👉 For more details, see our article on Salt and Brine for Fermenting Vegetables.

No Oxygen!

Lacto-fermentation is an anaerobic fermentation, which means that it requires no oxygen. If oxygen comes into contact with the vegetables, mould can develop and render the preparation unfit for consumption!

To avoid this, the vegetables must always be immersed in the brine.

Glass weights for fermentation

There are several techniques for keeping vegetables below the surface:

  • Glass weights
  • ViscoDisc-type counterweight
  • “Ziploc” style plastic bag filled with water, marbles, etc.
  • Cabbage leaf (be careful to submerge it too!)
  • Shooter glass, small plates, etc.
  • Ceramic fermentation weights

Choose food-grade plastic or glass. Acidity and salt could deteriorate certain metals and minerals, such as rocks.

Letting the CO2 Out

Fermentation will create carbon dioxide (CO₂), which is normal. If the container is hermetically sealed, the pressure will increase and the container may crack, or in the worst case, explode!

It is therefore essential to release this pressure (“degassing”) without letting any oxygen in. Jars specially designed for lacto-fermentation, fitted with valve systems to release the CO₂, are available on the market.

Airlock for fermentation

To evacuate the CO2, you have several options:

  • ⭐ Use lever jars (Le Parfait type): These jars degass on their own.
  • Use an airlock: This allows CO2 to escape while preventing air from entering. Very practical, as it fits both a Mason jar and a 50-litre boiler.
  • Leave the lids slightly unscrewed (by ¼ turn) for the first week, then put in the fridge.
  • Unscrew the lids slightly once or twice a day to let the gas out, then quickly reseal (risky technique).
  • Vacuum packing: A very practical technique for making small portions.

Not all techniques are equal. Our preference in terms of simplicity and success rate is to use quality lever jars.

After opening, keep your lacto-fermentation in the fridge to slow down fermentation and avoid contamination.

👉 For more information on fermentation weight options and how to evacuate CO2, see How to Choose Your Lacto-Fermentation Supplies.

Maintaining the Right Temperature

The temperature of the room where your fermentation takes place has a significant influence on it. In general, room temperatures are perfectly suited to home fermentation. The warmer the temperature, the faster the fermentation. However, it’s important to note that if the temperature is below 15°C, fermentation will be very slow, and if it’s above 30°C, fermentation will be too fast and could give poor results.

Recipe for crunchy pickles

Frequently asked questions

How Do I Know if My Fermentation Is Successful?

Successful lacto-fermentation is easy to identify:

  • Tangy taste and sometimes fizzy
  • A slightly vinegary smell
  • Sometimes cloudy brine

On the other hand, a failed lacto-fermentation will be recognisable by:

  • The presence of green, white, pink, or blue mould on the surface
  • A distinct smell of rot

👉 To find out more, see our FAQs on Lacto-Fermentation Problems.

How Long Does Lacto-Fermentation Last?

The minimum time required for lactic acid fermentation to take place is around 4 days. After that, the length of fermentation depends on your taste preferences and certain factors such as temperature, the size and type of vegetables, and the amount of salt.

The longer the fermentation, the richer the flavours and the more tender the vegetables.

  • Kimchi and pickles are often enjoyed after only a week of fermentation at room temperature.
  • Sauerkraut and root vegetable recipes, meanwhile, deserve to be refined over time and are delicious after one or two months of fermentation.
  • Fermented garlic‘s taste, on the other hand, metamorphoses after a year of fermentation.

If you’re a beginner, follow the recipe instructions, or leave to ferment for one to two weeks before placing in the fridge. To see how the flavour develops, try fermenting several small jars and tasting at weekly intervals.

Can I Transfer to Smaller Jars?

Yes, once fermentation is complete, you can transfer your preparation into smaller jars. You’ll then need to keep them in the fridge. If you notice that your fermentation is too dry for your taste, add a little 2% brine.

Can I Open My Jar During Fermentation?

You must not open the jars during fermentation. Doing so could expose the contents to the air, and therefore to various microorganisms present in the environment, which could contaminate your preparation. If you have ever opened a jar, it is advisable to keep it refrigerated afterward.

If you absolutely must open it and then wish to continue the fermentation process at room temperature, make sure that everything is well submerged in brine before resealing. If necessary, add a little 2% salty water. However, it’s best to put the jar in the fridge quickly. Even with only a few days of fermentation, lacto-fermentation is very tasty and healthy!

We do not recommend adding vegetables during fermentation.

When Should the Weights Be Removed?

You can remove the weights, inserts, and other accessories just before putting the jar in the fridge.

As long as the jar is at room temperature, we recommend leaving the accessories in place to keep the vegetables submerged. Fermented vegetables (if the jar has not been opened) have a shelf life of several years at room temperature. However, their taste and texture continue to change over time.

👉 For tips on prolonged storage, see our article on How to Preserve Vegetables with Fermentation.

Can I Change My Lid?

If you’re using a special fermentation lid, such as a lid with airlock, you can replace it with an ordinary lid once you’ve finished fermenting. Then place your fermentation in the fridge.

What Are the Deposits at the Bottom of the Jar?

The deposits you see at the bottom of the jar are a mixture of vegetable residues, salt, and various bacteria and yeast that are naturally present during the fermentation process. This is a completely normal and common phenomenon in lacto-fermentation, particularly with pickles.

It is important to note that the presence of these deposits is different from the formation of mould, which can appear on the surface if the vegetables are not completely immersed in brine.

What Are the Common Mistakes to Avoid?

Here’s a short list of common mistakes and how to avoid them to make your delicious fermentations a success.

  1. Letting in oxygen: Opening a lacto-fermentation jar in progress and leaving it at room temperature interrupts fermentation and exposes the contents to oxygen, promoting the growth of undesirable microorganisms. For prolonged storage after opening, refrigeration is essential.
  2. Adding the salt without measuring: You don’t need to be very precise about the amount of salt. However, if you don’t measure the amount of salt to add, your lacto-fermentation will be either too salty or not salty enough. The amount of salt does not vary with the length of fermentation, so once the salt has been added, it will be too late. Weigh your vegetables and add the right amount of salt.
  3. Using iodized salt: Iodized salt, as well as salt containing anti-caking agents, can disrupt fermentation. Check the ingredients list to make sure you’re using non-iodized salt.
  4. Vegetables not submerged: For optimal fermentation, make sure your vegetables are completely submerged from the start.
  5. Temperature too high: Above 30°C, vegetables will ferment too quickly, and the end result will be disappointing. Choose a lower temperature (15-25°C).
  6. Unsuitable containers: Although we encourage recycling and the use of materials that are already available, they must be suitable. So, watch out for metal lids that rust or leak, or weights that can’t withstand acidity…

👉 For more details, see 5 Mistakes to Avoid in Vegetable Fermentation.

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