Identify and eliminate errors

Sometimes things just go wrong. This is normal and not just limited to fermenting mistakes. Then roll up your sleeves and try again. Ideally, you should find out the reason why it went wrong, so that you can do it differently next time.

Note down your projects in a journal

Because things sometimes don't work out as expected, and one can learn so well from mistakes, I keep a diary about my ferments. At some point, I realized that it helps if I not only mark the ingredients and date on my fermenting containers, but also write down how I liked the ferment after opening and tasting it.

I strongly recommend keeping a fermentation diary as well.

For fermenting you should also have some experience in handling food. Temperatures, salt content and humidity are important - experience will help you here, or a glance at the F.A.Q.

What if the ferment stinks?

Unsuccessful ferments are quickly identified by their smell. Then you only need to go to the trash can or the compost and the problem is gone. Then the search for the source of the error begins.

When meat or fish are fermented, it is problematic that pathogenic bacteria can develop that cannot be smelled. That is why I do neither fish nor meat fermentations myself.

The ferment is slimy!

The finer the vegetables are chopped, the faster they ferment. In the case of extremely carbohydrate-containing vegetables, this often leads to foaming jars and/or the formation of a tough slime called dextran.

What is dextran?

Responsible for the formation of dextran is the lactic acid bacterium Leuconostoc mesenteroides, whose food is innumerable carbohydrates, including glucose, fructose or sucrose.

Although Leuconostoc mesenteroides is one of the psychrotolerant bacteria, i.e. cold-lovers, a temperature between 20 - 25 °C is considered optimal for growth. A temperature below 19°C, on the other hand, is unfavorable for other bacteria necessary for the safe fermentation process. Since you probably do not have laboratory conditions at home, it is rather difficult to hit exactly the degree in between. Therefore, if you have problems with dextran, I rather recommend to keep the available carbohydrates low.

Sometimes the environment is also to blame for the development of dextran because the bacterium crosses over. I once had a water kefir culture that developed dextran and infected some of my vegetable ferments. After I disposed of the kefir cultures, dextran no longer occurred.

In the food sector, dextran is also used as a thickener and stabilizer in bakery and confectionery products, beverages and ice cream. So it is not harmful! In the ferment, however, I do not appreciate it that much, the mouthfeel is strange - it is not without reason that it is nicknamed frogspawn bacterium...

Does foam on the ferment mean the ferment is bad?

If there is more metabolizable surface area for the bacteria, for example in the case of grated or otherwise heavily chopped vegetables, the faster and more violent the fermentation process. In the case of very carbohydrate-rich vegetables or vegetables with a lot of prebiotic ingredients (e.g. inulin in the case of beet or Jerusalem artichokes), this often leads to over-fermenting jars. Fortunately, this is not a problem at all. It neither tastes different, nor is it spoiled. The only thing that might bother is that the ferment overflows and stands in its own brine. Then you just put a plate or small bowl under the fermenting vessel and the issue is settled.

Stark schäumendes wildes Ferment.

What is the white layer on the ferment?

If you notice a white coating on your ferment, you need to analyze what it is. In most cases it is one of the two options mold or kahm yeast.

Molds appear as a white, in the course often colored, and furry coating. The spores spread through the air and form a mycelium if they find suitable living conditions. Exclusively on the surface of liquids they do not find these, they need an organic carrier substance.

The ferment is moldy

If nothing protrudes above the brine or is distended, it is almost certainly not mold. If so, please continue reading below about kahm yeast. However, if it is mold, there is no option - the entire ferment must be discarded. Skimming only a portion will not do, as mold spreads invisibly to the human eye. Then you should find out why mold was able to grow, so that it doesn't happen to you again. And if you are not sure, please rather dispose of the ferment before harming your health. Mold is a serious thing.

Fortunately, the white layer is in many cases not mold, but kahm yeast, which, on the contrary to mold, can grow on the surface of liquids.

What is kahm yeast?

Kahm yeast is a harmless biofilm of aerobic yeasts and oxygen-dependent bacteria that accumulates at the junctions of surfaces, e.g. brine or vegetables, with the air. They need oxygen to metabolize alcohol and organic acids, for example. In the past, this coating was called slimy skin (mycoderma). In the production of vinegars, for example, we want to achieve exactly this skin! On the surface of fruit or wine vinegar, a relatively solid kahm skin of acetic acid bacteria is formed by ethanol oxidation, which is called vinegar mother.

Unintentionally, kahm yeast usually occurs when your ferment has or had too much contact with oxygen. A typical beginner's mistake, for example, is not filling the jar or other fermentation vessel high enough. Then it takes too long for the advancing fermentation to produce enough carbon dioxide to displace the oxygen, and kahm yeast develops (optimally - at worst, mold develops). In addition, too high initial temperature can favor the development of kahm yeast.

Left: Kahm yeast on a beet - rutabaga - tonic with chili
Right: Kahm yeast on a carrot ferment. Carrots have a lot of inulin and many carbohydrates.

Kahm yeast is therefore not a problem and can be skimmed off or removed with a kitchen towel. However, it affects the taste and does not please everyone.

How to prevent kahm yeast?

  • Ferment in canning or flip-top jars. This prevents oxygen from the outside from reaching your ferment, but carbon dioxide from the fermentation process can escape through the rubber ring.
  • Ensure optimum filling level. The surface of the brine should end two fingers wide, or 1-2 inches below the top of your flip-top jar.
  • Under the brine is fine! Everything must always be under the brine! Layer your vegetables cleverly and if possible cover them with some kind of weight.
  • Pay attention to the temperature. Your ferment will go through different microbial phases, each of which needs specific temperatures to create the best possible development environment for the desired bacteria.
  • Lactofermentation works well with salt. Salt provides a perfect environment for beneficial lactic acid bacteria, while kahm yeast cannot develop well in a salty milieu.


  1. Hallo Katsu,
    probiere gerade das fermentieren zu lernen, dabei ist mir Deine Seite sehr hilfreich, Danke!
    Jetzt hab ich aber ein Problem, vielleicht kannst Du mir raten:
    Ich habe Champignon mit etwas Zwiebel im Glas, beschwert mit Gewicht und an einem warmen Platz gestellt. Jetzt ist das Gewicht gesunken und die Pilze schwimmen oben und die Lake ist unten. Kann ich die trotzdem noch essen und was kann ich beim nächsten mal anders machen?
    Danke schon mal
    und Dir herzliche Grüße
    aus Murnau am Staffelsee

    • Lieber Rupert,

      ich freue mich, dass Du hier soviel findest, was Dir weiterhilft. Zum Thema Champignons in Salzlake kann ich Dir leider keinen Rat geben, ich fermentiere keine rohen Pilze. Was ich jedoch weiss, ist, dass wenn das Milieu schon anaerob war, als das Gewicht verrutschte, nicht viel Schaden angerichtet werden kann. Wenn fermentierte Champignons also etwas Gutes sind, dann vielleicht auch noch nach dem Verrutschen des Gewichtes…

      Trau Deinen Sinnen beim Öffnen. Solltest Du Schimmel entdecken, muss das Ferment entsorgt werden.

      Toi toi toi,

  2. Hallo Katsu,
    Schön, dass ich bei fast allen Fragen direkt schon hier Antworten finde. Ich liebe deine Seite und bewundere dein Fachwissen immer wieder.
    Nur noch mal um sicher zu gehen, Kahm wird dann also auf Essig die Mutter und muss entsprechend nicht entfernt werden?

    • Liebe Steffi,

      vielen Dank, das freut mich, wenn diese Sammlung Dir helfen kann.

      Ja, wenn die Kahmhaut sich aus Essigsäurebakterien bildet, wird sie zur Essigmutter werden. Das habe ich schon bei vielen meiner Essige beobachten können. Zu Anfang war ich unglücklich über die störende Kahmhaut, nun weiss ich es besser und freue mich auf die entstehende Essigmutter.

      Viel Spaß beim Fermentieren!

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