The Ultimate Fermentation Troubleshooting Guide

Published · Updated

Welcome to the uglier side of fermentation. You looked in your jar and saw something weird—a blob, a film, or a fuzzy patch. Now you are panicking.

Don’t throw it out yet! Fermentation is a biological process, and it isn’t always pretty. 90% of the time, that “weird thing” is perfectly normal. This guide will teach you how to spot the difference between harmless yeast, annoying Kahm, and dangerous mold.

📚 Specific Troubleshooting Guides

Looking for a specific problem? Check these deep-dives:

⚠️ The Golden Rule of Fermentation Safety

“When in doubt, throw it out.”

While this guide will help you identify many issues, your health is not worth risking over a €5 batch of kefir. If you are genuinely unsure if something is mold, discard the entire contents and sanitize your jar thoroughly. Better safe than sorry.

The “Big 3” Identification Guide

Every weird growth usually falls into one of these three categories. Apply these tests to your jar.

🛑 1. MOLD (Dangerous)

Mold is a fungi that you do NOT want. If you see this, the batch is ruined.

  • Texture: FUZZY, hairy, or dry. It looks like bread mold.
  • Color: Blue, Green, Black, bright Orange, or pure White fuzz.
  • Location: Always sits on top of the liquid and grows upward.

ACTION: Toss everything. Sanitize jar. Buy new grains/SCOBY.

⚠️ 2. KAHM YEAST (Harmless)

Kahm is an aerobic yeast. It isn’t dangerous, but it tastes bad (funky/yeasty).

  • Texture: A thin, dusty, dry film across the entire surface. It often looks wrinkled like a brain or flat matte paint.
  • Color: Always White, Cream, or pale Tan. Never colorful.
  • Location: A skin across the very top surface.

ACTION: Skim it off. Taste the brew. If it tastes okay, continue. If too funky, restart.

✅ 3. NORMAL (Safe)

Healthy fermentation is often ugly. These are all signs of a healthy culture:

  • Yeasty Strands: Brown/tan slimy strings hanging off the SCOBY or floating in kefir.
  • Blobs: Smooth, gelatinous lumps (baby SCOBYs or grain growth).
  • Sediment: Brown dust at the bottom of the jar (dead yeast).

ACTION: Celebrate! Your culture is alive and working.

The 5-Second “Is it Mold?” Test

Still unsure? Perform these two simple checks.

Test 1: The “Fuzz” Check

Look closely at the growth side-on. Does it look like tiny hairs or velvet growing up and out of the liquid?

YES = Mold 🛑
NO (It’s slimy/smooth/dusty) = Likely Yeast/Kahm ✅

Test 2: The “Submerged” Check

Is the weird blob floating *under* the surface of the liquid, even just slightly?

YES = Normal Yeast/Grain ✅ (Mold requires air, it cannot grow underwater).
NO (It’s dry on top) = Do the Fuzz Check again.

❓ Panic FAQs

It smells like sulfur / rotten eggs!

This is usually stressed yeast, common in Water Kefir that has too many minerals. Give it a few batches with plain white sugar and water to clear it out. It’s unpleasant, but rarely dangerous.

It smells like nail polish remover (acetone).

This means the yeast is starving and turning alcohol into acetone. Your brew has gone too far. Discard the liquid and start a new batch immediately with fresh sugar/milk.

My Kombucha SCOBY sank. Is it dead?

No. SCOBYs can float, sink, or hang out in the middle. It makes no difference to their health. A new baby SCOBY will eventually grow on top anyway.

There are tiny white things moving in my jar!

Vinegar Eels or Fruit Fly Larvae. This means your cover wasn’t tight enough. The batch is ruined. Toss everything, sanitize heavily, and use a tighter cloth next time.

My Milk Kefir has yellow/orange crusty bits on top.

If it’s hard and crusty, it’s likely just dried milk cream that got pushed to the top. It’s harmless. Just scoop it off. If it is fuzzy orange, it’s mold.

Did you have mold? Start fresh.

Don’t risk your health. Get guaranteed clean, active cultures delivered.

🛒 Buy Fresh Kefir Grains & SCOBYs