Every new brewer has the same week-one moment: something pale, wrinkly, or stringy appears in the jar, and the question arrives — is that normal, or is it mold? Here is the honest field guide. When in doubt, the rule is absolute: mold means the whole batch goes — SCOBY and all. Your backup culture (see the SCOBY hotel on our SCOBY page) makes that an easy call instead of a heartbreak.
Normal — keep brewing
- A new SCOBY layer: smooth, cream-to-tan, slightly translucent, forming across the surface. May start as a thin film or blotchy patches that merge — ugly, then beautiful.
- Brown stringy bits: yeast strands hanging under the SCOBY or floating. Perfectly normal, if unappetizing.
- Bubbles trapped under the SCOBY and a gentle vinegary smell — fermentation doing its work.
- Kahm yeast: a flat, wrinkled, matte white film. Not dangerous, but it can make a batch taste off — most brewers skim it or restart for flavour. It is the SCOBY world's common cold, not its plague.
Mold — throw it all out
- Fuzzy, dry patches — mold looks like the mold on old bread: raised, powdery or hairy spots, usually on the surface.
- Colours: green, black, blue, or bright white fuzz. Healthy SCOBY growth is smooth and wet-looking; mold is dry and fuzzy.
- Location: mold starts on top, exposed to air — often at the jar's edge.
If it's mold: do not taste, do not "save the good part," do not feed the SCOBY another chance. Discard batch and culture, wash the jar hot and thoroughly, and restart from your hotel or a fresh SCOBY.
Why mold happens (and how to stop it)
- Weak start: too little starter tea, so acidity fell too slowly. Use 1–2 cups of strong starter per gallon.
- Cold room: slow fermentation gives mold a head start. Aim for 24–29 °C; a heating wrap fixes a cold kitchen.
- Contamination: unwashed hands, soap residue, or a loose cover letting fruit flies in. Wash, rinse well, cover tight.
- Flavouring the main jar: fruit and oils belong in the bottle, never in the primary brew.