Kombucha mold: how to spot it and when to discard a batch

What mold on kombucha looks like

• Dry, fuzzy, hairy, or powdery patches are the clearest warning sign.
• Growth usually appears on the surface or on culture left above the liquid, where oxygen is available.
• Colonies may begin as separate round patches and spread as they grow.
• Blue, green, grey, brown, or black fuzz matches the contamination described in food safety guidance. White fuzz can also be suspect.
• No single color, shape, or position identifies every contaminant. Treat these features as warning signs, not a laboratory diagnosis.

Mold can grow before the sweet tea acidifies enough, and spoilage yeasts or other contamination can also alter the surface. Submerged brown yeast and wet pellicle folds are common, but appearance cannot establish safety. If the growth is fuzzy or unexplained, discard the batch without tasting or sniffing it closely.

What is not mold, even if it looks scary

• Brown strands or clumps below the surface are commonly yeast from the fermentation.
• Bubbles, holes, and ridges can form when carbon dioxide collects beneath a young pellicle.
• A new pellicle often starts as a wet, translucent film and may form in separate patches.
• A flat, wrinkled film is often called kahm yeast by home brewers. That name cannot confirm which organisms are present or whether the batch is safe.
• Flat brown deposits inside or beneath an older pellicle are often yeast and tea sediment.
• A pellicle may sink, tilt, or form in separate layers; its position does not diagnose contamination.
• A tart vinegar note can occur in normal kombucha, but smell cannot prove that a batch is safe.

1. Healthy pellicleWet and translucent when young; it may turn cream or tan as it thickens.
2. Yeast strandsBrown strands or clumps below the surface are common during fermentation.
3. Kahm yeastA flat, wrinkled film often called kahm. Its appearance does not confirm safety.
4. MoldDry, fuzzy patches on the surface indicate spoilage. Discard the batch.

Kahm yeast

Home brewers use “kahm yeast” for a flat, pale, wrinkled surface film. You cannot identify the organisms in that film from a photo, and authoritative kombucha guidance does not classify it as harmless. A flat film lacks the raised fuzz typical of mold, but that distinction does not turn it into a safe ingredient. If an unplanned film appears, especially with an off odor or stalled acidification, discard the batch. Do the same whenever you cannot confidently separate the film from mold. Do not skim the film and use the tea as starter for another brew.

The one-minute check

1. Leave the surface undisturbed and inspect it from above and through the side of the jar in good light.
2. Look for dry fuzz, hairs, or powder on top. Wet folds and submerged brown strands more often come from the pellicle and yeast.
3. Check whether the growth rises above the surface. Round patches can support a mold call, but shape alone is not enough.
4. Treat blue, green, grey, brown, black, pink, or orange surface growth as contamination. White growth still needs a texture check.
5. Notice odors from a normal distance. Do not lean over the jar and inhale mold spores; a musty or rotten odor is reason to discard.
6. If the surface remains unexplained after this check, discard the batch. Keeping a suspect jar warm for another day only extends the contamination.

What to do if it is mold

1. Discard the tea, the SCOBY, and every pellicle layer from that jar. Do not pour any of it into a SCOBY hotel.
2. Move the jar away from open food before emptying it, and avoid shaking or scraping the dry growth. Wash the jar and reusable tools with detergent and water, rinse them, then sanitize with a food-safe method used exactly as directed. Cleaning removes residue so the sanitizing step can work. Let every item air-dry instead of wiping it with a used towel, and replace the cloth cover rather than trying to brush it clean.
3. Restart with a fresh culture and active starter liquid from an uncontaminated source.
4. Before the next batch, check the recipe, starter amount, cover, temperature, and every surface that touches the brew.

USDA guidance says to discard moldy high-moisture foods because contamination can extend below the visible surface. Kombucha guidance from the BCCDC and University of Georgia gives the same instruction for contaminated tea and SCOBY. A photograph cannot identify the mold species or rule out toxins.

Why mold happens

• Not enough active starter liquid, or a recipe that fails to acidify the sweet tea as expected.
• Starter taken from a contaminated, poorly stored, or inactive culture.
• Fermentation outside the temperature range specified by a tested recipe, which can slow normal acid production.
• Hands, jars, utensils, cloths, or ingredients that introduce unwanted microbes.
• A pellicle or solid ingredient left above the liquid, creating an exposed surface where mold can grow.
• A loose or damaged cover that lets in dust, fruit flies, or other pests.
• Fruit, herbs, or other raw flavorings added during first fermentation, before the tea has reached its target acidity.

Smells, fruit flies and other worries

A tart, vinegary, or yeasty smell can accompany normal fermentation, but odor does not test food safety. A musty or rotten odor means discard; do not sniff the jar closely. Fruit flies are a separate contamination problem. Check the underside and edge of the cover as well as the pellicle, since adults can enter through gaps or damaged fabric. If you find eggs or larvae, discard the batch, clean and sanitize the equipment, and replace the cover. On the next brew, secure a tightly woven cloth with a band all the way around the rim.

Pink or orange surface growth does not belong in a normal batch. Color cannot identify the organism, so discard the tea and culture rather than scraping the patch away.

How to prevent it

• Follow a tested recipe and use its full amount of active starter liquid. The liquid acidifies the sweet tea; the pellicle alone does not do that job.
• Keep the jar within the temperature range in the recipe and track whether fermentation progresses as expected.
• Wash, rinse, sanitize, and air-dry the jar and reusable tools before they touch a new batch.
• Secure a clean, tightly woven cover that allows airflow while keeping out dust and pests.
• Keep the brew away from compost, spoiled produce, smoke, splashes, and open bins.
• Keep the culture and other solids in contact with the liquid instead of leaving them to dry on the jar wall.
• Store backup culture in a separate SCOBY hotel so one contaminated jar does not take every starter you have.

Do not guess at a dose of vinegar when you are short of starter. Household vinegars vary, and adding vinegar does not replace an active culture or a tested process. Start a smaller batch that preserves the starter ratio, or obtain more uncontaminated starter before brewing. If a batch does not acidify as the tested recipe requires, discard it instead of trying to rescue it late with vinegar. How to make kombucha and what a SCOBY is explain the role of starter liquid.

Frequently asked questions