Judith Browning wrote:
I've been skimming off a thin white layer from the top every few days...like when I make some fermented vegetables. Should that be happening?
I would imagine that's kahm yeast.
The Oracle (bot) says:
Kahm yeast is a harmless, thin, white or creamy film that forms on the surface of fermented foods and beverages like sauerkraut, pickles, or kombucha, typically due to the presence of oxygen and warmer temperatures. While not harmful to consume, it can affect the flavor and texture of the ferment, so it's often skimmed off the top. To prevent kahm yeast, maintain a consistent, cooler temperature, ensure the food remains submerged, and use clean equipment to create a less hospitable environment for its growth.
What is Kahm Yeast?
A harmless surface film:
Kahm yeast is a type of wild yeast that appears as a thin, often powdery or crinkled, white or cream-colored layer on the surface of ferments.
A natural occurrence:
It is a natural phenomenon that occurs when wild yeast, present in the air and on fresh ingredients, grows on the surface of a ferment where there is contact with oxygen.
Conditions for growth:
It thrives in warmer temperatures (above 70°F/21°C) and prefers an oxygen-rich environment, which is why it forms on the surface, unlike molds or beneficial bacteria that may be submerged.
Why it forms
Oxygen exposure:
The presence of oxygen is key for kahm yeast to develop and form a pellicle, similar to a SCOBY in kombucha.
Temperature:
Warmer air temperatures accelerate its growth, while cooler conditions slow it down.
Fermentation dynamics:
In a dynamic fermentation process, lactic acid bacteria consume sugars and produce lactic acid, creating an acidic environment that inhibits harmful bacteria but allows kahm yeast to grow.