Mold – When Things Get Ugly

Fermentation is fun. There are only a few strict rules to follow, and the rest is the matter of the will to experiment and to be open to unexpected results that are nice more often than not.  Nothing can go seriously wrong unless

…. you manage to grow mold.

This is nasty. Mold produces poisonous mycotoxins, and you should never eat it.

However, be aware that not all fungi growing on food are mold. To be classified as mold, fungus must form multicellular filaments, something like tubular threads, which create a network called mycelium. On the contrary, the harmless yeast lives in colonies made of singular cells.

Therefore, you can easily distinguish one from another. If you can see a smooth white film covering your veg, relax, it’s just yeast, and it will not do you any harm. Some people even enjoy the taste. If you don’t, just skim it from the surface or rinse off with water. This creature is called kahm yeast by fermenters, but I don’t think it’s a scientific term.

I don’t have a proper picture of kahm yeast, but you can see the initial stage of its growth here. Note, there is no lid nor airlock, because the picture was taken in Poland where people know that a layer of kahm yeast isolates a ferment from oxygen in the air.

On the other hand, the poisonous mold can have different colors, from black to green, red and pink and have an uneven, ‘threaded’ structure. It also makes the food discolor and change its texture giving it an unmistakable ‘spoiled’ look. And smell. Your nose will make you sure that you are not going to eat this. It’s repulsive, while kahm yeast’s aroma is rather neutral or mildly sour.

How to prevent from growing mold on your precious ferments?

1. First of all, always keep vegetables submerged in brine. Mold can only live in the presence of oxygen. If you ‘burp’ your jars, make sure to pour a bit of brine on top of the veg if you can see that its level is low.
2. Don’t skimp on salt. Yes, it’s recommended to use as little salt as possible, so you do not turn sauerkraut into salty junk food. But, be reasonable. You don’t want to turn it into rotten cabbage either. Use at least 1 tablespoon of salt for 1 kg of fresh veg. Read more.
3. Don’t overheat the jars. It’s recommended to put them in a warm place at the start of fermentation; warm place means room temperature, not a sauna.
4. Mind you, pesticides present on the surface of the product can also play a role. They make vegetables more susceptible to mold. If it grows every time on your ferments, no matter how careful you are, consider buying organic vegetables next time.

All in all, be aware that your fun with fermenting can sometimes be spoilt. However, in normal conditions, it happens very rarely and is highly preventable.

So, don’t worry and keep fermenting!