Mould on a Kombucha SCOBY: Is It Still Safe to Drink?

Is it dangerous to drink kombucha if the SCOBY has mould?

If the growth is genuinely mould, stop drinking it and discard the batch. Not the visible patch — the whole vessel, the liquid and the pellicle together. This is the conservative position and it is the right one here, because kombucha gives you no way to check the thing that actually matters.

The visible colony is the fruiting body of an organism whose mycelium has already grown through the pellicle and into the liquid beneath it. Some of the moulds that colonise kombucha, particularly Aspergillus and Penicillium species, can produce mycotoxins that are not neutralised by the acidity of the brew and are not visible, tasteable or smellable. There is no home test that separates a harmless surface contaminant from a toxin-producing one, and no way to know how far it has already spread.

What does mould on a SCOBY actually look like?

Mould is dry, fuzzy and raised. It sits on top of the pellicle rather than in it, in roughly circular colonies with a defined edge, and it looks like the mould you would find on bread or citrus — because it usually is the same genera. Colour is commonly blue-green, grey-green, black or a chalky white, and texture is the giveaway: hairy or powdery, never wet.

It grows only where the brew meets the air. Mould cannot establish below the liquid, so anything you see underneath the surface is not mould, whatever colour it is.

What gets mistaken for mould on a kombucha SCOBY?

A new pellicle. Every fermentation grows a fresh layer at the surface, and it begins as a thin, translucent, uneven film before thickening into a smooth cream-coloured mat. In its first days it can look patchy and alarming. It is flat and wet rather than raised and fuzzy, and that is how you tell.

Yeast. Brown or dark tan strands hanging beneath the SCOBY, or settled as sediment at the bottom of the vessel, are yeast colonies. They are supposed to be there — they are half of the culture. Dark brown patches on the underside of the pellicle are the same organisms.

Kahm yeast. A flat, wrinkled, white film spreading across the surface is kahm yeast rather than mould. It is not dangerous, but it competes with the culture and leaves a musty flavour. Unlike mould it lies flat against the liquid and carries no raised fuzz.

Why did mould grow on my kombucha?

Almost always because the brew was not acidic enough, soon enough. A fresh vessel of sweet tea is a comfortable substrate for a great many organisms; what makes it kombucha’s alone is a pH low enough to exclude them, and that has to be there from the first day rather than earned over the first week.

The mechanism is starter liquid, not the pellicle. Adding 10–20% mature, unflavoured kombucha by volume to a new batch should put it at or below pH 4.5 immediately. A brew started with a pellicle and little or no liquid can sit near pH 6 for days, and that is the window in which mould establishes. The other common contributors are a vessel left open or sealed airtight instead of covered with a breathable cloth, flavourings or oils added to the primary ferment, and a fermentation temperature below about 20 °C, which slows acidification without slowing mould.

Can I save the SCOBY by cutting the mould off?

No. Cutting away the visible colony removes the part you can see and leaves the part you cannot; the mycelium runs through the cellulose mat, which is porous by nature. The same applies to rinsing it, soaking it in vinegar, or peeling off the top layer.

Start again with a pellicle and starter liquid from a source you trust, wash the vessel in hot soapy water and rinse it thoroughly, and give the new batch a proper acid head start. If mould returns across separate batches with fresh starter, look at the room rather than the brew: a nearby fruit bowl, compost bin, houseplant or damp patch will keep reseeding the surface with spores.