This is the part that trips up almost every new brewer at some point, so let's be honest about it.

Totally normal:

• Brown stringy bits hanging from the bottom of your SCOBY, that's just yeast, it's harmless and actually a sign of a healthy culture

• Your SCOBY sinking to the bottom, it doesn't need to float to do its job

• A new thin layer forming on the surface, that's your baby SCOBY forming, a good sign

• Slightly uneven or patchy colouring, completely fine

• A vinegary smell, that's what healthy fermentation smells like

Not normal — stop and take a closer look:

• Fuzzy growth in green, black, or pink; that's mould, and unfortunately the batch needs to go. A healthy SCOBY won't have fuzzy spots.

• A very unpleasant smell that isn't just vinegary, trust your nose on this one

• Slimy texture beyond the usual firm-but-gelatinous feel

The good news is that mould is actually pretty rare if you start with enough starter liquid and keep your equipment clean. Most of the time what looks alarming is completely harmless.