Problems With Lacto-Fermentation (FAQ)

You’ve just done a lacto-fermentation (vegetable fermentation), and you’re wondering if everything is going well in your jar? Think you’ve got a problem?

First of all, don’t panic! Lacto-fermentation is very safe. Thanks to the acidic environment created by the good bacteria, no harmful bacteria can develop, as they cannot tolerate acidity.

So, there’s no risk of botulism, salmonella, listeria, E. coli or anything else. In fact, fermentation is safer than raw vegetables and canned food!

If your lacto-fermentation fails, the signs are unmistakable: repulsive smells, hairy mould on the surface, flashy colours, etc.

Read on to discover the different phenomena that can occur in your jar. While some situations are normal, others may indicate a problem.

If you had to remember just one piece of advice, it would be this one:

When in doubt, rely on your senses. If it smells or tastes bad, throw it out!

Go straight to your question:

Mould and yeast

Colour change



Flavours and textures

Mould and Yeast in Fermentation

Is it normal to have a white film on the surface?

If there’s a whitish layer on the surface of your lacto-fermentation jar, it’s probably a biofilm called “Kahm yeast”. It’s harmless!

Microorganisms can build up a delicate, white biofilm that doesn’t smell much. This film covers all or part of the surface of the liquid in your fermentation jar.

Kahm yeast may appear when the fermentation temperature is high (above 25°C), or when the brine is low in salt.

Kahm yeast on lactofermentation

This biofilm is harmless to health. However, it can alter the texture and taste of vegetables. It is, therefore, better to remove this film with a spoon and place the jar in the fridge.

Tip: Keeping the fermentation in a cool place can prevent or reduce the development of Kham yeast.

What Are the White Particles at the Bottom of the Jar?

White deposits at the bottom of the jar are normal – they’re partly yeast and leftovers from fermentation (salt, sugar, etc.).

Rest assured: in lacto-fermentation, everything that happens below the surface is harmless.

What Should I Do if There’s Mould in My Fermentation?

Moulds have a powdery, felted, almost “hairy” appearance. They are often blue, green, gray, black, or sometimes white.

The picture below shows examples of mould in fermentation.

Fermentation mould

If mould has settled in your fermentation jar, unfortunately, you’ll have to throw it out and start again. Remember to sanitize your equipment before trying again.

If there is mould, it’s because your vegetables weren’t covered sufficiently by the brine (and therefore came into contact with oxygen), or that there was too much free space in your jar. Next time, follow our complete guide to lacto-fermentation.

We don’t recommend eating foods with mould.

However, many fermenters remove the mouldy part, especially when it’s small, (and whatever is no longer submerged in brine), and eat the vegetables below, if they have a good smell and texture. At your own risk!

Colour change

Why Has My Fermented Garlic Turned Blue or Green?

Garlic sometimes turns blue or green during fermentation. This is normal and harmless!

This colour change is due to a compound in the garlic that reacts to the acid in the fermentation process. This does not affect the taste or texture of your fermented garlic. Everything’s fine, you can eat it!

To find out more, see Why Does My Fermented Garlic Turn Blue or Green?

Is It Normal for the Colour of My Vegetables to Change During Fermentation?

Yes, the colour of vegetables often becomes duller during fermentation. Some vegetables, like beetroot or red cabbage, can also colour the rest of the jar.

For example, we use a small beetroot to colour the turnips in our recipe for Fermented Lebanese Pink Pickled Turnips!

Lactofermented turnips and beetroot

However, if there’s a dramatic colour change, it’s bad. It’s extremely rare, but if, for example, your carrots turn black, your sauerkraut turns pink or your cauliflower turns bright orange, and there’s no logical explanation, trust your common sense. Throw it out!


Why Has My Brine Disappeared?

Fermented vegetables sometimes become dry during fermentation.

There are three possible reasons for this:

  • The vegetables have reabsorbed the brine
  • CO2 pressure produced by fermentation pushed the brine out of the jar
  • The brine has evaporated over time

Notice a lack of brine in the first 4 days of fermentation? You can open the jar and pour in a little salt water to cover the vegetables. Before closing, make sure that all the vegetables and the weight are well covered.

Notice a lack of brine after 4 days of fermentation? Don’t touch anything. The oxygen in the jar has probably been expelled by the CO2 produced during fermentation, creating a small plug that protects the vegetables.

Should My Brine Become Cloudy?

Yes, it’s perfectly normal for your lacto-fermentation brine to become slightly opaque and whitish. It’s not dangerous!

Some vegetables, like beans or pickles, will turn the brine white in a few days. This means that the good bacteria are doing their job!

Cloudy brine during lactofermentation

The floating particles will eventually settle at the bottom of the jar, and the brine should clear up slightly over time.

Why Has My Brine Become Slimy?

Lacto-fermentation brines can become slimy, but this phenomenon is harmless. It is caused by harmless bacteria.

Possible causes:

  • Fermentation temperature too low or too high
  • External source of bacteria (whey, etc.)
  • Very sweet vegetables (e.g. beetroot)

Tip: if you don’t like the texture of your lacto-fermentation, you can incorporate it into dishes such as salads, stir-fries, or soups.

My Brine Is Making Bubbles! Is This Normal?

Yes, it’s perfectly normal! Fermentation is going well and creating CO2, which is trapped in the container. Let the little bubbles do their thing 😉

On the other hand, there are no bubbles in your jar and no sign of fermentation? If you’re still in the early days of your recipe, be patient. Fermentation is a process that is not always visible.

Your fermentation was very active in the first few days, but since then there’s been no sign of life? Once again, this is completely normal. Some fermentations are very active for the first few days, and then settle down.

Lacto-Fermentation Smells

Is It Normal for My Lacto-Fermentation to Smell of Sulphur?

It can happen. Some fermented vegetables may smell of sulphur after fermentation, but they still taste delicious and are harmless.

Onions, radishes, and cruciferous vegetables (cabbage, cauliflower, etc.) can smell of sulphur. This smell is often present in the first few days of fermentation but disappears with prolonged fermentation.

It’s like the smell of a strong cheese… One day, you’ll love it ;)

My Fermentation Smells of Vinegar, but I Didn’t Add Any…

A vinegary smell at the end of fermentation is perfectly normal. The environment in which your vegetables are immersed has become more acidic and, with that, comes a smell and taste reminiscent of vinegar.

Note: lacto-fermentation contains lactic acid, whereas vinegar is made of acetic acid. Vinegar generally smells and tastes spicier.

My Jar Smells of Putrefaction. Is This Normal?

No. Lacto-fermentation should not smell of rotting vegetables.

If you can’t put the jar under your nose because the fermentation smells bad, throw it out! Use your common sense.

Vegetable Texture and Salt

Is It Normal for My Vegetables to Become Soft?

Yes, vegetables tend to soften during fermentation. Don’t worry, they’re still very tasty.

Several factors influence texture:

  • Fermentation time
  • Salt concentration
  • Temperature
  • Type of vegetables used

Tip: Incorporate fermented vegetables that have become too soft into sauces or soups.

For your next trials, consider adding a source of tannins (oak leaf, raspberry leaf, grape leaf, etc.) or calcium chloride to keep them crunchy!

To find out more about the factors that affect texture, read How to Preserve Vegetables with Fermentation.

My Fermentation Is Too Salty! What Can I Do About It?

Have you dropped the salt shaker in your sauerkraut recipe (or any other fermentation recipe)? The easiest thing to do is to rinse it off straight away or add more vegetables until it tastes just right.

The salt content does not decrease during fermentation. If it’s too salty on day 1, it will be just as salty on day 30.

If you realize that your fermentation is too salty when you’re ready to eat it, you can rinse it (but you’ll lose a lot of flavour and nutrients) or start a new one by incorporating the old one with an equivalent or greater quantity of fresh vegetables.

Follow the normal lacto-fermentation procedure and let it ferment for at least a week.

A final option is to consume your over-salted fermentation by adding it to other dishes with little (or no) salt.

Click here to find out more about salt in lacto-fermentation.

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