Mold and spoilage

A sugary liquid is an excellent growth medium, and in an unpasteurized product the only things stopping anything are acid, cold and cleanliness.

Three different organisms

Mold, which needs air and grows on a surface.

Yeast, which ferments and produces gas and alcohol.

Bacteria, which sour, slime or produce off-flavors.

They look and smell different and they arrive by different routes, and telling them apart is the first step to fixing the cause.

Mold on a ferment

The one every kombucha maker meets: fuzzy growth on the surface of the culture, blue, green, black or white and raised.

It is not the culture. A healthy kombucha pellicle is flat, wet and attached; mold is dry, fuzzy and sits proud.

The answer is unambiguous: discard the batch and the culture. Do not skim it, do not rinse it, do not keep the liquid. Mold grows roots you cannot see and produces compounds you cannot taste.

Then find the cause: too little acid at the start, too little culture, a contaminated vessel, dust, or a cloth cover that got wet.

Yeast and bacterial spoilage

Yeast spoilage shows as gas, haze, and a beery or solvent smell in a product that should not be fermenting. In a bottle it is refermentation.

Bacterial spoilage shows as ropiness or sliminess, a vinegary or buttery smell, or a product that has simply gone sour.

Both mean something got in after the process that should have excluded it, which points at filling, at the container, or at cleaning.

Where it comes from

Fruit, which arrives with a surface load and brings more if it is damaged.

Dry botanicals, which carry their own load into a product with no kill step.

Hoses and gaskets, which are the hardest things in the plant to clean and a common reservoir.

Containers, which are not sterile as supplied.

Air, in an open fermentation, which is why the cover matters.

And water, if a treated water store has been standing.

References