Has Your Sauerkraut Fermentation Gone Bad? Three Fermentation Rules and Many Troubleshooting Tips

Are there uninvited guests lurking in your jar of sauerkraut? Most likely not.

It can be very unnerving to leave a jar of vegetables on your counter to ferment for weeks on end. It is even more disquieting to find mold growing, pink splotches – Are they from outer space? – or to get a pungent whiff of some god-awful smell when opening your jar of fermenting sauerkraut.

Do you fear that your fermentation has gone bad and you will poison your family?

In the case of fermented vegetables, such fear is unfounded.

As far as I know, there has never been a documented case of food-borne illness from fermented vegetables. Risky is not a word I would use to describe vegetable fermentation. It is one of the oldest and safest technologies we have. – Fred Breidt, microbiologist, US Department of Agriculture

But, you ask!

What are those nasties growing on my sauerkraut?

Why do I not see any bubbles? Does that mean fermentation is not happening?

Or, my sauerkraut is too mushy. What caused that?

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Three Basic Fermentation Rules

Keep these basic rules in mind as you learn this time-honored skill of preserving foods. Have fun along the way.

Want to make sure nothing goes wrong with your sauerkraut fermentation? Visit my recipe How to Make Sauerkraut in a Jar in 7 Simple Steps [Healthy, Flavorful, Easy] for numerous tips and step-by-step instructions with plenty of photos.

I’ve broken my troubleshooting tips into broad categories to help you figure out what is happening in your jar or fermentation crock. It is rare that you will find a situation where your sauerkraut needs to be tossed. Usually, what you are seeing is normal and can be fine-tuned by adjusting the temperature at which you’re fermenting and how long you’re fermenting.

I’ve included some images from the Comments section where readers have uploaded their pictures of moldy, slimy, brown sauerkraut. Such pictures are worth a thousand words. 🙂

Things Growing on My Sauerkraut

The sudden invasion of green and black fuzzies or a white powder on your precious ferment can be rather alarming prompting even the hardiest of us to toss it all and vow to never ferment again.

Please be patient and take the time to figure out what went wrong. Or, what went “right” to allow the mold or yeast to take hold. Molds and yeasts are rare if the basic rules for fermentation are followed.

Kahm Yeast

Kahm can describe a number of yeasts that will sometimes show up on the surface of a ferment that hasn’t reached a high enough acidity.

Kahm yeast is a flat, thin, white to cream-colored powder and if it grows thick enough, it can almost look like velvet. The yeast can also appear as a creamy scum if it forms and then the brine level drops below the surface.

You may see Kahm yeast raised from the surface of your brine if air bubbles get trapped by the Kahm yeast layer.

Kahm yeast takes hold at the beginning of fermentation if the required high acidity level of your ferment is slow to form. It appears most often during warm weather and when fermenting sweeter vegetables, such as beets, carrots and peppers. Its growth is often an indicator that not enough salt was used.

It can look scary and unpleasant and even smell a little strong, ranging from yeasty to cheesy or even reminiscent of alcohol. Although harmless, Kahm yeast is something you don’t want to let overgrow since it affects the flavor of what you are fermenting.

A few years back, I tossed a jar of sauerkraut that had strange creamy-white threads of who-knows-what working their way along the top layers. I now know it was Kahm yeast with a strong alcohol smell to it. Too far along to even consider eating. Read about it here.

What to Do If You Have Kahm Yeast Growing on Your Ferment

Due to its powdery nature, it can be hard to remove, and once it has invaded your jar, it tends to reappear after removal, even when stored in your refrigerator. To make removal easier, wait until fermentation is complete – or even cut it short – remove all of the yeast, including what is stuck to the jar and then taste the top layer. If it tastes of Kahm yeast, remove until you get down to a section that tastes fine. Then, repack your sauerkraut into a clean jar.

This is a time to thoroughly clean your jar, crock, lid or whatever came in contact with this batch of sauerkraut, perhaps using a distilled white vinegar solution.

Mold

Mold is raised and fuzzy and can be white, black, blue, green or even pink. Mold grows from mold spores that are present everywhere in the air and on the surface of fruits and vegetables.

Mold begins growing when spores land – or already exist – on a wet nutrient-rich surface, such as bits of exposed cabbage, and over time grows into a thick layer. They can actually survive in acidic foods so it’s not necessarily the acidity that deters them. But don’t grab your bleach bottle and try and sterilize your jar and lid trying to kill these mold spores. You’ll be killing off the bacteria just the bacteria you need.

All bacteria and fungi produce what are called, in scientific terminology, ‘competitive factors.’ Lactobacillus produces lactic acid and hydrogen peroxide that is lethal to mold spores. The faster the Lactobacillus takes hold, the less likely you’ll have mold. And a perfectly sterile environment is not good for the bacteria, just like it’s not good for the mold. – Wild Fermentation Forum

Another blogger has more on mold in ferments with lots of pictures here.

This picture from one of my readers shows some mold. Their cabbage floaties trap was out of the brine and exposed to air and mold grew. Toss the offending piece. The rest is fine.

First off, rarely should you have mold growing on your ferment. If you do, don’t get mad and think you will never figure out fermentation. Instead, treat the mold as a big Thank You! from the mold spores. You established the perfect home for them to grow: air, warmth and not enough little salt.

Figure out exactly why the mold grew and adjust the next batch accordingly.

Should You Salvage a Moldy Ferment or Be Safe and Toss It?

This is a personal question that you will have to answer. I’ll share my insights but leave the final decision up to you.

Mold spores are everywhere. We can’t eliminate them.

If the environment is right, mold spores will grow and multiply on the surface of your ferment. This is fairly common with open crock fermentation where the nutrient-rich surface of the ferment is in contact with oxygen-rich air. Usually, underneath the mold growth, your ferment is untouched and smells fresh and clean.

The few times I’ve made the decision to toss a jar of moldy sauerkraut, I have removed that top layer of nasty looking stuff to unearth wonderful, tangy and fresh smelling sauerkraut. I stop mid-toss as my hate-to-waste side kicked in and it was saved from the compost pile and enjoyed by the family.

Most find it perfectly safe to remove the layer of mold on top of their ferment. This is fine with greenish or grayish mold. However, toss ferments with black, pink or orange mold or if they have an off smell.

If you are not comfortable salvaging a ferment or are sensitive to molds, by all means, throw it all out!

Hi Holly, The last lot of Skraut smelled vile! It has been very hot for a few weeks and I thought it had gone off. I decided to put it in the Kompost and as I tipped it out I realized that just under the top it looked quite ok and smelled good. I tasted it and it was delicious. Surprise surprise, I think it is quite hard to ruinSauerkraut. I eat it every day and I think it helps to keep the cancer at bay!

Thanks! Anna

How to Salvage a Ferment that has Mold

Remove mold or other surface growth, as best you can as soon as you see it. The longer you allow the mold to grow, the deeper it penetrates your ferment. Molds can digest pectins, leading to mushy vegetables. Molds also digest lactic acid, the crucial preservative in your ferment.

Gently remove your weight from your fermentation vessel, then use a large spoon to get under the mold and skim it off the best you can. Evaluate the texture of the underlying ferment, removing any layers that are soft or discolored. If you have pH strips, test your ferment, looking for a pH reading below 4.0.

Since mold needs lots of oxygen to grow, it doesn’t hurt to then stir the brine layer a bit to submerge any microscopic mold spores you may have missed, thus depriving those microscopic beings of the oxygen then need for survival.

A Watch Pot Never Bubbles: Bubble Issues

During the first few days of fermentation, you should see little champagne-like bubbles slowly moving through the sauerkraut and rising to the surface.

These bubbles are most predominate during the initial few days when the first bacterial strain to go to work (L. Mesenteroides) are eating the sugars in your cabbage and vegetables. This produces carbon dioxide, hence the bubbles. Their work also increases the acidity of the brine. You may hear an occasional fizzy sound as the bubbles work their way out of your jar, either through your loose lid or an airlock.

Though this is one of the key fermentation signs, don’t panic and toss your jar if you don’t see bubbles. They can be elusive and not every batch of sauerkraut progresses through each stage with perfect timing. You are not fermenting in a climate-controlled laboratory!

Help! No Bubbles! My Ferment had Died

Keep Calm!

The bubbles are most likely in your jar but you can’t see them because they are trapped in the packed fermentation mixture. Remember, if it is past the first 5-7 days, you may no longer see many bubbles, if any.

There is a Growing Foam-Like Mass of Bubbles Creeping Out of My Jar

With some batches of sauerkraut (usually those exceptionally high in natural sugars), you may see a foam-like mass of bubbles collecting on the surface of your ferment. The bubbles may even be colored depending on what you used to flavor your sauerkraut. Beets will leave a dark-red to brownish scum of bubbles.

Brine Issues

Brine. That essential salty, nutrient-rich fluid that keeps our ferment safe from airborne molds and yeasts. Sometimes, it is so copious that it flows out of the jar and onto our countertop. Other times, it just disappears and leaves our sauerkraut high and dry.

Help! I Have Too Much Brine. It is Spilling out the Top of My Sealed Jar

The first week of fermentation is when visibly your ferment is most active. Gases created during this first stage of fermentation need to push their way up and out of your packed sauerkraut. If these air bubbles instead get trapped in your packed sauerkraut, the mixture will expand and move up in the jar. This is called “heaving” and results in either brine pushing up and out to make a puddle around the jar or brine trickling down into available air pockets to make the top your sauerkraut looks dry.

The amount of brine produced in your fermenting sauerkraut can vary dramatically from one batch to the next. Generally, you’ll have more brine at the beginning of fermentation and during the part of the day when your house is warmer. Ideally, you do not want to lose this precious brine. It helps to keep your ferment anaerobic and provides moisture in your jar of finished sauerkraut.

Cloudy Brine

Cloudy brine is perfectly normal and actually a sign that fermentation is progressing. You may also notice some white sediment forming at the bottom of the jar. This white powder is from the bacteria and is perfectly normal. Some say it is caused by dead cell walls from the vegetables floating around. Others say it is from iodine or anti-caking agents found in some salts.

If your sauerkraut contains beets, turmeric or other deeply colored vegetables, you may see the brine change to match the color of what you are fermenting. You may also notice dirty specks of color – especially when using carrots or beets – forming at the top of your jar. All is good.

It is fine to consume cloudy brine; it is loaded with B-vitamins.

Brown Brine

This picture from one of my readers shows some brown brine.

When fermenting during warm weather, you may notice that your brine turns brown. Harmless but rather unappetizing. Try to cool things down with one of these tips.

Slimy Brine

This picture from one of my readers shows some slimy brine.

The first time slime found its way into one of my jars of fermenting goodness was with the popular Ginger Carrots recipe in Sally Fallon’s book Nourishing Traditions. Many of us have had a similar experience. We’re lured in by the opening of the recipe: “These are the best introduction to lacto-fermented vegetables we know.”

The high sugar content of the carrots invites in unwanted microorganisms that prefer the high sugar vegetables.

Sauerkraut with thick, stringy, slimy brine occasionally develops early on in the fermentation process due to the production of dextrans by rapidly growing strains of Lb. cucumeris and Lb. plantarium bacterium. Dextrans are high molecular weight polysaccharides made from glucose molecules, hence the slippery, syrupy brine.

This occurs especially at elevated temperatures or when fermenting vegetables high in sugars, like beets, carrots or sweet peppers.

Not Enough Brine

When you are massaging the salt into your cabbage you may notice that you have to work harder and longer to get a puddle of brine. The cabbages you used to make your sauerkraut could have dried out in storage. I have a whole post devoted to dry sauerkraut.

There are two times of the year cabbage is grown: spring and fall. In the spring, cabbage is ripening during longer, warmer days, which drys it out. In the fall, cabbage is ripening during shorter, coolers days which makes for sweet, densely packed heads.

Texture Issues

The texture of your finished ferment can range from melt-in-your-mouth soft to hurt-your-teeth hard with everything in between. Variations in batch occur throughout the year usually due to the temperature at which you are fermenting.

Sauerkraut that is Too Soft

If you prefer sauerkraut with a nice crunch, it can be heartbreaking to open up your jar to find mush.

Soft sauerkraut results when bacteria that normally do not initiate growth until the later stages of sauerkraut production actually grow earlier usually due to too high of fermentation temperatures or not enough salt. You can’t rescue the current batch but for future batches, adjust one or all the Salinity, Temperature and Time dials. See also How Long To Ferment Sauerkraut?.

Sauerkraut that is Too Crunchy

To achieve a softer texture, adjust one or all the Salinity, Temperature and Time dials. See also How Long To Ferment Sauerkraut?.

Flavor Issues

Be mindful of how your sauerkraut tastes and work with fermentation parameters until you get it right. Life is too short to eat blah sauerkraut!

Not Enough Tang

The sour flavor in sauerkraut comes from lactic acid produced by the lactic-acid bacteria (LAB) eating the sugars in your cabbage and vegetables. Once all the sugars have been converted to lactic acid, your max levels of tang have been reached.

Too Salty

Sometimes too much salt gets mixed into our ferment, resulting in overly salty sauerkraut. Or, if you have been restricting your salt intake, sauerkraut may seem overly salty to you. Some sources say to rinse the sauerkraut. Doing so rinses off some, but not all of the beneficial probiotics. Personal preference along with the type of salt you used will play a factor in how salty your finished sauerkraut tastes.

Color Concerns

As sauerkraut ferments, the bright green of the cabbage slowly fades to become almost pale white at the end of fermentation. This is normal. What if your sauerkraut turns pink? Brown?

Pink Sauerkraut

Pink sauerkraut can be quite beautiful and is great if it comes from red cabbage, beets red kale or even some fruits. But sometimes, pink color in sauerkraut is caused by pigments produced by the growth of certain types of yeasts. These yeasts may grow if there is too much salt, an uneven distribution of salt or if the kraut is insufficiently covered during fermentation. The yeasts that cause pink sauerkraut are not considered harmful and the sauerkraut is perfectly safe to eat.

Brown Sauerkraut

Over time, a jar of sauerkraut stored in your refrigerator will darken slightly. This is normal and perfectly fine to eat.

If instead, there is a brown layer of sauerkraut at the top of the jar, that portion of sauerkraut is oxidized. Air got to that section of sauerkraut and caused it to turn brown.

Since it is protecting the sauerkraut below, leave it alone, move your jar to the refrigerator and when you are ready to eat from the jar, remove and toss the oxidized layer.

Smell Issues

Funky old socks? Gym sweat? Farts? Rotten eggs? Stinky Swiss cheese? Sulfur? Even bleach! Those are a handful of the terms used to describe what fermenting sauerkraut can smell like. Thankfully, not every batch will produce these off-putting odors.

Natural Fermentation Odors

According to Kirsten and Christopher Shockey, authors of Fermented Vegetables – that I reviewed here, most of the stink periodically experienced in fermentation is caused by the production of naturally occurring fatty acids. For reasons unknown, some batches produce one or more of these acids in quantities that affect the smell.

Propionic acid is often described as smelling like human sweat or dirty socks or can also smell sulfurous like flatulence. Caproic acid smells like goats. Butyric acid smells like rancid butter. Isovaleric acid smells like a stinky locker room

Sulfur-containing compounds found in cabbage – and other cruciferous vegetables – can also produce strong and pungent odors.

Just remind yourself the numerous nutritional benefits they are packed with as your nose adjusts to the odors. Rest assured, however, your sauerkraut is still safe to consume.

Pungent Odors

If, however, your sauerkraut smells like rotting or putrid food, you’ll want to toss it. Putrid is an unmistakably awful odor that might even make your eyes water. Usually, molds, yeasts or an off-color accompany truly putrid smelling sauerkraut.

Invaders: Fruit Flies and Maggots

If you are fermenting in an open crock or not able to put a lid on your jar of fermenting sauerkraut, both flies and fruit flies can find it and lay their eggs on the surface. The result? Maggots crawling out a few days later.

Though most prevalent during warmer months, fruit flies can be a problem all year-round. They are attracted to ripening fruit, fermented fruits, tomatoes, melons, squash, bananas, potatoes and onions. If I notice fruit flies, I set a few fruit-fly traps around my kitchen. I share two favorites, below.

Remove Infested Layer

If you do find maggots in your crock of sauerkraut, there is no need to panic or discard the whole batch.

As they hatch on the surface of a ferment, maggots migrate up and out of the food; they do not burrow farther down. Remove the top inch or so of the fermenting vegetables, and go as deep as necessary until you reach sauerkraut with no signs of maggots, no discoloration and a pleasant aroma. Be sure to wipe the interior sides of the vessel to remove any lingering maggots or eggs. – Sandor Katz, The Art of Fermentation

WOW! That should cover just about anything that could go wrong with your ferment. Let me know if I missed something.

Remember the Basic Fermentation Rules

This should cover any imbalances you might encounter in your jars as you explore the wonderful and wild world of natural fermentation. Do not let them scare you away. Follow the basic rules of fermentation:

You will be successful! My recipe covers it all. Go give it a try and you might never need to visit this post again.