Most of the time, what looks alarming is a normal SCOBY. Real mold is usually fuzzy, powdery or dusty, and forms distinct patches. If you see fuzz in any colour, throw the whole batch out. If you’re unsure, a close look at the texture and smell usually settles it.
Healthy SCOBY vs mold: quick checks
| What you see | What it usually is | What to do |
|---|---|---|
| Smooth, rubbery, creamy-white to tan mat (darker with black tea) | Healthy SCOBY | Keep brewing |
| Ridges, holes, tears or wrinkles | Healthy SCOBY | Keep brewing |
| Brown or black stringy strands hanging below the mat | Yeast, normal | Keep brewing, and strain them out if you prefer |
| Thin, see-through or patchy new film | A young SCOBY forming | Give it time |
| Wavy, flat white film, without fuzz | Kahm yeast | Discard the batch and start again |
| Fuzzy, furry, powdery or dusty patches in white, grey, green, blue or black | Mold | Discard everything |
| Rotten or putrid smell | Spoilage | Discard everything |
Dark brown or black colour alone isn’t mold, since black tea darkens a SCOBY. Fuzzy black patches are mold.
Why it’s easy to confuse
- A new SCOBY starts thin and patchy. It can look see-through or mold-like for a while (BBC Good Food).
- Yeast strands and cloudy spots are normal. They hang below the mat or form a haze.
- Texture matters more than colour. Mold is fuzzy or powdery and sits on the surface. A healthy film is smooth or ridged and slightly rubbery.
- Sinking isn’t mold. A SCOBY that drops to the bottom is a different question. See why does my SCOBY sink?
Signs your brew is healthy
- The liquid is getting less sweet and more tart.
- A new film is forming or thickening.
- Small bubbles appear.
You don’t need all three. It is normal for only one to show at first.
What to do if you see mold
- Don’t taste it, and don’t scrape off the fuzzy part and keep the rest.
- Throw out the whole batch, along with the SCOBY and the starter liquid.
- Clean the vessel with hot soapy water, rinse it well and let it dry.
- Start again with a fresh SCOBY and at least 10% strong starter tea. How to grow a SCOBY from scratch has the full method.
What causes mold and how to prevent it
Mold usually comes from contamination, such as an unclean vessel, dust, or the air around the jar. It can take hold when the brew isn’t acidic enough yet. To reduce the risk:
- Use at least 10% strong starter tea in every batch.
- Keep the vessel and your hands clean.
- Cover the jar with a tight-weave cloth, which keeps out dust and fruit flies.
- Keep the brew warm enough to acidify. A cool room slows acidification, which gives mold a longer window.
Fruit flies and maggots
Fruit flies are drawn to fermenting liquid, and they lay eggs in it. If you find maggots, throw the whole batch and the SCOBY away. Use a tightly woven cloth to keep them out, since loose cheesecloth or muslin can let them through.
If you feel unwell
If you feel unwell after eating or drinking a batch you suspect was moldy, contact a health professional. For other warning signs in a homebrew, see is homemade kombucha safe to drink?