Fermenting vegetables is simple and problems rarely occur when following a few basic requirements. The beauty of dealing with living microorganisms is that they usually politely do what they should, though at times they have a mind of their own so unexpected things do happen.
Below you’ll find common questions about problems during fermentation and what could be done to avoid them.
Problems during fermentation
The two main reasons for fermentation problems are:
- Wrong temperature (most often too warm)
- Too much contact with air (jars not airtight, or too little brine)
Stay in control of fermentation
Use a starter culture. A starter culture makes fermentation more stable and predictable. A good starter contains potent bacteria strains that quickly take control of fermentation in the jars and suppress the growth of harmful microorganisms like mold.
Unwanted microorganisms. Unwanted microorganisms can cause the breakdown of proteins and produce an undesirable flavor and changes in texture. However, most problems can be avoided with good hygiene and the right temperature.
Good hygiene. Use clean tools, utensils, and jars. Clean your hands and rinse all vegetables in water.
Soft, mushy vegetables
One reason for this is because the temperature is too high during the initial 5-7 day fermentation. I’ve had this problem a few times. Once left the jars to ferment in a cupboard close to the stove. When using the stove, the temperature in the cupboard was raised which affected the fermentation process. The vegetables were still okay to eat but they were too soft and mushy.
This experience gave me a vital lesson—control the temperature. Crunchy fermented vegetables are much more enjoyable than mushy ones.
If you’re fermenting vegetables without a starter culture (wild fermentation) there are additional factors to consider.
Wild fermentation is not entirely wild because it follows stages in which different bacteria strains grow in a certain sequence. However, if this sequence is changed or disturbed, it often results in mushy vegetables.
Without a starter, controlling the temperature is even more important. You might also want to add more salt to the veggies as this helps to keep mold in check. But it’s easier to use a starter.
Dark-colored vegetables
The most common reason for this is the presence of unwanted microorganisms during the fermentation process. Another, but not so common problem, is too much salt in the jars. This disturbs the growth of some probiotic strains and promote unwanted salt-tolerant bacteria and yeast.
Another common cause is allowing a too low brine level in the jars causing unwanted bacteria and yeasts to grow on the surface of the vegetables that are not covered by brine. This can cause a discoloring (often brown) and a bad flavor. However, if you intend to consume the veggies quite fast, then this might not be a big problem because it takes time for the discoloring to develop.
If the temperature is too high during fermentation, this can cause the growth of undesirable microflora resulting in a darkened color. But dark coloured veggies at the top does not always mean the taste is bad. Discard the veggies on top and the rest might be enjoyable.
NOTE: Try filling the jars 70% with veggies, the rest with brine. Make brine by juicing celery (or cabbage). Use enough brine to completely cover the vegetables in the jars. When fermentation is complete and you put the jars in a cool place, check brine levels. It has a tendency to decrease after a a few days in the fridge. Top up with filtered, cool water.
Pink sauerkraut
Using red veggies like cabbage or beet root will color the entire batch. However, if non-red vegetables turn pink, then this is often caused by a group of yeasts that produce an intense red pigment.
For sauerkraut the reason can also be too much salt, or an uneven distribution of salt. This can allow yeast to multiply. But this is rare.
If your green vegetables have turned pink, you might not want to eat those.
A whitish or colorful layer on the surface
Usually a whitish layer floating on the surface is a yeast called kahm yeast. It can develop as the lactic acid bacteria consume all the sugar and the pH of the ferment drops. This layer of yeast may have a textured surface almost resembling spaghetti. Just remove the white layer and discard it. The vegetables below the surface should still be fine to eat.
A common reason for kahm yeast is that vegetables are not submerged in brine, or the container is not sealed well.
Maintain an air-free environment for the vegetables. Follow the instructions given in other posts about how to cover the surface with cabbage leaves to keep the fermenting vegetables submerged in brine. Mold more easily develop in warmer temperatures, so during fermentation try to keep your veggies in a location that does not get over 70°F.
Colorful layer of mold on the surface
Again, culturing temperature is too high or vegetables are not fully submerged in the brine. If you’re not using a culture starter, you might need to add more salt in the brine to prevent bad microorganisms to grow. However, don’t add too much as it might disturb the good bacteria.
Another cause for mold are if harmful microorganisms are present on the vegetables before you ferment them. Unclean equipment or covering cloths can also cause this. Rinse all veggies thoroughly.
If mold is present in the jars, it best not to consume the vegetables. They will most likely be unpalatable and unhealthy.
Foamy brine—as it should be
During fermentation bubbles in the jars will form as the bacteria start consuming sugar. Using vegetables containing more sugar promotes foaming; beets, apples, and carrots are a few. Foaming is normal and usually subsides after a few days. Some brine might leak out when pressure builds during the first stage of fermentation. If lids are very tight, try open them to let excess gas out during the first few days.
Strong odor
During fermentation, the good bacteria are transforming sugar into other complex substances as acid and gas. This is normal, but it can also smell quite strong. However, it should never smell rotten or mold.
If your batch smells rotten or mold, then something might have gone wrong. Too high temperature is a common reason. Also, unclean equipment, dirty hands or a poor culture starter can all contribute to this. If your batch smells really awful, you might not wan to consume it. Taste it to make sure.
Slimy brine
If slime-producing microorganisms are present, your brine will look unappealing. Again, a too high temperature can cause this, but also too little brine in the jars so that some vegetable are not covered. Some pickles can also cause the production of slime. In some cases, the veggies might still be enjoyable.
Too much salt
Not very common. But if you add too much salt you risk changing the sequence in which different bacteria work. This is especially so with wild fermentation. or not using a starter culture. Try adding more liquid to the jars to dilute the salt. Use freshly pressed cabbage or celery juice. You can also use filtered, cool water.
The veggies taste much better with salt. I’ve fermented many batches both with and without a starter culture and in my experience using culture starters is far better. However, only use a high-quality culture starter.
Brine leaking out from jars
This is normal and happens every time I prepare my batches; jars are bubbling and some brine is leaking out. It shows that the good bacteria is hard at work.
This is the reason why it’s best not to fill the jars completely full with vegetables. Fill your jars 70% full, this leaves more space for the brine to expand in the jar. During the fermentation process don’t put the lid on too tight, just enough to shut air out but also allowing gas to escape from the jars. The pressure in the jars can be very high, like in a bottle of Champagne.
White sediment
Yeasts can settle at the bottom of the jars. But as long as the vegetables look and smell fine, they should be good to consume. However, if they are slimy or look moldy, you might want to be careful.
Cloudy brine
During fermentation lactic acid is created which can create a cloudy brine. Lactic acid is what gives the fermented vegetables the tangy, refreshing taste which is considered very healthy.
Dull, faded vegetables
At the start of the process vegetables might be very colorful. I often use 5 to 10 different vegetables in my mix and most have strong colors. But after a few days of fermenting the veggies turn pale, or the entire jar might turn pink. This is because the friendly bacteria in the jar is transforming the vegetables, including the colors. This process is essential and shows that fermentation is well. In most cases, the ready product will not have the same color as the original vegetables.
Blue or green garlic
Some specialists believe this is due to different metals reacting with pigments in the garlic. It has happened to me a few times when fermenting garlic. The garlic does not seem to be harmed in any way and the taste is great. It just looks funny. However, be careful of fermenting garlic together with other vegetables as the garlic will dominate the taste. It might be better to ferment garkic in separate jars. But if you are a garlic-lover, then just go ahead!
Can’t see if fermentation has started
In a lower room temperature, fermentation might need more time. Ideally, good microorganisms need around 70°F for optimal fermentation. At 60 degrees fermentation will slow down, but not stop. In fact, fermentation continues even when put in a fridge, only very slowly. Taste the vegetables every two, three days to determine when they are ready. In the winter I’ve fermented vegetables for 10-15 days and the result was still great. So be patient and taste regularly from the jars.
Use a good starter culture to minimise fermentation problems.