When fermenting vegetables, it is common to notice a white layer forming on top of the liquid after a few days. Often this white film is mistaken for mold, and the entire ferment is discarded. However, the white film is usually a type of yeast known as kahm yeast.
Kahm yeast is not harmful, although it may be unattractive or even smell a little odd. It should be removed from the ferment so it does not impart a bad odor, but a little bit left in the jar is not harmful to the vegetables or to you.
KAHM YEAST CAN FORM FOR A VARIETY OF REASONS:
- The batch is insufficiently acidic.
- There is not enough salt in the brine.
- The culturing temperature is too warm
- The batch is over-exposed to oxygen.
- Good hygiene was not observed during preparation
WHAT TO DO ABOUT KAHM YEAST
If kahm yeast develops in your ferment, skim it off the surface of the liquid. Discard any solid matter that has it. As usual, your senses are the best test: if it smells and tastes okay, it probably is fine to consume. A sour aroma is normal, but an unpleasant, spoiled or rotten-food aroma is not.