How to Ferment Vegetables (Lacto-Fermentation 101) (2024)

What is lacto-fermentation?

Lacto-fermentation is at its core a food preservation process—and it's the same one that's been used for thousands of years. Without our modern refrigeration methods, our ancestors relied on fermentation to preserve food for later consumption. And the interesting thing is that without knowing the science behind why it worked like we now do, they used only their own intuition. I like to remind myself of this when I'm preparing my own ferments as it helps remind me to use all of my senses to guide me beyond just getting the salt ratio right. It really is an art and a science.

It's important to point out that we are focusing on fermenting vegetables here, but you can also lacto-ferment fruits using the same method. Additionally, lactic acid fermentation (as it's more formally called) is responsible for the characteristically sour taste of fermented dairy products like yogurt and kefir. The difference there, though, is the process. Instead of adding salt, fermented dairy is created by using an existing starter culture of bacteria to inoculate a new batch.

There are other types of fermentation and fermented foods as well, including alcoholic fermentation used to make beverages such as wine and beer, acetic acid fermentation used to make vinegar, and butyric acid fermentation used to make certain cheeses. And just to note, the term "lacto" doesn't refer to dairy at all in the context of vegetables; it instead refers to the lactic acid produced by the fermentation process.

Fermented vegetables

Getting back to fermenting vegetables, the important thing to know is that the lacto-fermentation process encourages friendly bacteria (mainly Lactobacillus) to convert the natural sugars in your produce into lactic acid by way of added salt. The lactic acid not only acts as a natural preservative to deter the growth of harmful bacteria during fermentation, it also preserves the ferment for later use and alters the taste, texture and nutritional profile of the original food.

So what started out as just cabbage is now a delightfully sour and tender yet still crunchy condiment known as sauerkraut. It's just science, but it really is magical.

Choosing vegetables

In order to optimize for the best success with home fermentation, step one starts with deciding on the source of your produce. If possible, buy local and organic vegetables. The less the produce has been touched by pesticides and handled and transported, the better your ferment will be. Remember, we are relying on the natural bacteria living in and around the produce to kick-start the ferment, so the closer to its natural and fresher state the better. If you live in an urban area like me, you can look for local farmers markets or CSA farm share options.

Equipment needed

As promised, you don't need any special equipment other than a lidded Mason jar to get started fermenting!

I like to have both pint-sized Mason jars as well as quart-sized Mason jars on hand depending on the size of the ferment. For example, these fermented carrots fit perfectly into a small pint-sized jar, while a sauerkraut ferment normally needs at least a quart-sized container to fit a whole head of cabbage.

The only other item I'd recommend if you think you'll be fermenting on a regular basis is some glass fermentation weights. These serve to hold down your vegetables underneath the salt brine which is very important to avoid mold (since lacto-fermentation is an anaerobic process.) In the case of some ferments, though, you may not need weights at all. For carrot sticks, you can just wedge them into the jar tight enough so that they don't float, and for sauerkraut a nice trick is to use a clean cabbage leaf to tuck and keep everything submerged underneath.

Step by step guide

No matter what produce you've chosen, this quick guide will apply to all ferments no matter the size.

Step 1: Prep

First and foremost, always make sure to start with clean hands whenever you're fermenting at home. Since we're using good bacteria in fermentation, we don't need any extra bad bacteria getting in the way and crashing the party. 😉 You'll also want to wash your produce unless you picked it yourself from a clean/organic source. For non-organic produce that can be peeled such as carrots, you should also peel the produce before fermenting. Then, proceed with slicing or chopping according to the specific recipe.

Pro tip: While clean jars and kitchen utensils are obviously recommended throughout the process, it is not necessary to boil and sanitize everything unless you want to. Even though this is a requirement in the case of canning, fermentation allows for a little less stringent prep since the salt itself helps kill any bad bacteria it encounters while preferentially encouraging the growth of good bacteria to crowd out the bad.

Step 2: Brine

The next step is to surround your prepped produce with brine, and there are two different methods to accomplish this depending on type of produce. In both cases, you'll determine the correct salt ratio based on the weight of the produce and water combined.

• Brining - for hard vegetables without a lot of their own water content (such as carrots), you'll prepare a "brine" which is just water* and salt
• Dry salting - in the case of vegetables or fruits with a higher water content (such as cabbage), you'll directly salt the produce which will encourage the produce to "sweat" and form it's own brine

*Pro tip: Make sure to use filtered, non-chlorinated water when preparing a salt brine, as chlorine can affect the success of the ferment. If you don't have access to filtered water, you can boil tap water first and let it cool in order to remove the chlorine from the water.

The specific fermented vegetable recipes you choose will tell you which method to use.

Salt for fermenting

When it comes to lacto-fermentation, the type of salt you use is important. Sea salt, Himalayan pink salt, kosher salt or any other finely ground pure salt work well for fermentation. Just make sure the salt you choose doesn't contain any anti-caking agents or iodine as both of these additives can affect the success and/or taste of the ferment. A good rule of thumb is to simply avoid using table salt and use one of the other salts listed instead.

Lacto-fermentation salt ratio

Whether you use brining or dry salting as your method of fermentation, the most important key is to determine the salt ratio for your specific ferment.

Using sauerkraut as a reference point since it has a solid base of published research, my target salt ratio window when fermenting vegetables is a 2-5% salt concentration by volume. As a general rule, I usually shoot for a 2.5% salt concentration for my vegetable ferments. I find that specific ratio yields fairly predictable results and delicious, successful ferments.

The salt ratio is based on the total weight (or volume) of the vegetables and brine combined, whether you're brining or dry salting.

Here are two examples to make this clear:

Example 1: Fermented carrots

In the case of this fermented carrots recipe which requires brining, I know that the volume will be roughly 15 liquid ounces (425 grams) including carrots and water. (A pint-sized Mason jar is 16 ounces and I'm leaving a little room for the ferment to breathe and bubble.) And I know that the weight of my salt (fine ground Celtic sea salt) is about 5.2 grams per teaspoon. So, the 2 teaspoons of sea salt specified in the recipe would equal 10.4 grams, which is 2.45% of the weight of the ferment (425 grams), the perfect amount. Other vegetable ferments will be similar assuming you're using the same sized jar and similar salt (for quart-sized jars, simply double the amount of salt.)

Pro tip: To keep the ratio as precise as possible, you can simply sprinkle the salt over the carrots or other veggies once they are packed into the jar, and then pour the water over everything until it's about an inch from the top of the jar. Otherwise, you'll need to pour water in first, pour it out and add salt to it, and then add the combined salt brine back into the jar (since the amount of water will vary depending on the volume of the carrots.) I find that eliminating the extra step of mixing the salt into the water separately works out just fine, especially in the case of quicker ferments taking less than a week.

Example 2: Sauerkraut (fermented cabbage)

In the case of sauerkraut which uses dry salting instead of brining, all you'll need to do is weigh the sauerkraut and then multiply that weight by 2.5% to determine how much salt to add. Using a baker's scale makes this calculation easy if you ferment a lot, but a regular calculator works too! Just weigh your cabbage, multiply by 2.5% and weigh out that amount of salt. You can look for an inexpensive kitchen scale or postal scale to weigh the salt; it's not necessary to invest in a baker's scale unless you want to.

Pro tip: Once you've measured and salted your cabbage in a large bowl, let it sit for several minutes to allow it to start "sweating". Then, use your own clean hands to massage it for another 5-10 minutes until you are left with a nice brine of juice in the bottom of the bowl. You can then pack in into your Mason jar and pour in the brine to cover.

Step 3: Ferment

Once you've brined and packed your veggies, take a look to make sure there are no air bubbles in the jar. The goal is to eliminate any bubbles and avoid mold, so you'll want to make sure to really pack down your ferment one last time if necessary.

Then, secure the ferment either with a larger piece of the produce such as a cabbage leaf, or by packing in larger cut produce such as carrot sticks so that nothing floats to the top. If needed, you can use fermentation weights to keep everything under water.

Cover your jar loosely with a lid and choose a location on your countertop or in a cupboard that's at room temperature and away from direct sunlight.

Fermentation temperature

The ideal temperature for fermentation to take place is around 65-70°F (18-21°C), give or take a few degrees. If your room is on the cooler side, fermentation will be slower, and vice versa in a warmer room.

Fermentation time

Typically, fermentation time will range from a few days to a few weeks or more. Depending on the vegetables or fruits, you'll have different recommended fermentation times and you should refer to the specific recipe for timing.

As your ferment progresses, you may notice some cloudiness and/or bubbling going on. Both are completely normal and expected. Each day, loosen the jar a little to "burp" your ferment and let any built up carbon dioxide escape. Then, re-tighten the jar but still loosely.

Pro tip: If fermentation goes quickly, you may notice a little overflow. To prevent a mess, you can place your jar on a saucer or into a shallow plastic container to contain any brine that overflows.

You can taste your ferment anytime during the fermentation process, but I typically start taste-testing towards the end of the fermentation time suggested. If the flavor is not strong enough for your liking, simply keep fermenting.

Step 4: Store

Once the taste is just where you want it, just pop your ferment in the fridge in the same covered jar and that will end the fermentation process. Congratulations; you successfully completed your ferment! 🙂

Most vegetable ferments should last at least three months in a covered jar in the fridge, but many can last months longer. If it looks, smells and tastes good, it should still be fine.

Recipe ideas

There are unlimited possibilities for fermenting vegetables and fruits, and even more possibilities for flavors you can add. Feel free to experiment with adding a little fresh garlic, dill sprigs, bay leaves, peppercorns or other spices to your various ferments. Or, combine vegetables or fruits for even more variety! It's so much fun to taste the final flavors and incredibly rewarding to know that you created your own unique ferment to boot.

Here is a short list of ideas to get you started:

• Sauerkraut (fermented cabbage)
• Fermented carrots
• Preserved lemons
• Pickles (fermented cucumbers)
• Kimchi (traditionally Napa cabbage, Korean radishes and other veggies and spices)
• Fermented beets or other root vegetables
• Fermented garlic, onions or peppers
• Fermented asparagus or green beans
• Fermented tomatoes
• Fermented apples or berries

Once you have some ferments going, check out these recipes with fermented foods for some inspiration on how to use your fermented veggies in everyday meals.

Troubleshooting

If you've followed the guide above and things don't seem quite right, don't worry! Even the most experienced fermenters will have an off batch here and there, and there are some basic troubleshooting steps you can take to either course correct the current batch or determine if it's necessary to start a new batch.

Odd smell/taste/color

While this is somewhat subjective, you'll likely know when things just seem "off" either by the way they look or smell during fermentation. A little cloudiness is perfectly normal, but change of color may not be. Use your senses to guide you here and go with your instincts. If the end result doesn't taste right, it's best to err on the side of safety and start a new batch.

Mold

If you see mold develop on the surface of your ferment, the most likely causes are either air exposure or contamination. Prevent in the future by using a fermentation weight (if needed) to keep veggies under the surface, and making sure to have clean hands, wash produce well depending on the source, and use clean equipment. A tiny bit of mold on the surface can simply be scooped out and your ferment should still be just fine. If it has penetrated deeper into the ferment, however, you should start over with a new batch.

Kahm yeast

If you see a white film develop on the top of the water (called kahm yeast), that's also quite normal and you can just skim it off when you see it. Kahm yeast is often mistaken for mold, but it's actually harmless.

Slimy vegetables

If you notice your veggies are softer than expected or appear slimy, they may have been over-fermented and you may need to discard the batch if slimy. Make sure your room temperature is in the recommended range of around 65-70°F (18-21°C) for future ferments, or end the fermentation process sooner. Another culprit may be the use of table salt that has anti-caking additives or iodine. Make sure you're using pure salt such as sea salt or kosher salt.

What kind of salt should I use to ferment vegetables?

The best kind of salt to use for fermenting is pure salt such as sea salt, Himalayan pink salt or kosher salt. Avoid table salt or other salt that contains anti-caking agents or iodine for best results fermenting.

What's the correct salt ratio for fermentation?

The ideal salt ratio for lacto-fermentation to take place is a 2-5% ratio of salt to total volume of the ferment including the brine. This ratio will assure that you are creating the ideal environment for fermentation to take place.

Why aren't my vegetables fermenting?

The most likely causes of under-fermentation are cold temperature, not enough salt or insufficient fermentation time. Make sure your room temperature is around 65-70°F (18-21°C) and that you've used a 2-5% salt ratio based on the volume of your ferment.

Why is my ferment bubbling over?

If you're using regular lids on your fermentation jar, make sure they're not tightened too tightly and open them up a little each day to "burp" your ferment and allow any CO2 gas buildup to escape. You may also want to place a saucer or shallow container under your jar to contain any overflow.