A sick kombucha is rarer than the internet suggests. Only one sign means the batch is lost. A dry, fuzzy patch on the surface, blue, green or black. Brown strings, bumps, holes, a sinking SCOBY, a thin new layer and a sour smell are all normal. The six other common complaints come down to temperature, starter liquid or time, and all six are fixable.
Most messages we get about a sick kombucha describe something completely harmless. That is understandable: a jar of fermenting tea looks alarming the first time. This page sorts the seven things people actually see into three groups, and tells you which single one means you have to start over.
Remember one sentence and you will never need this page again. Mould is dry, fuzzy and sits on top of the surface. Everything wet, smooth or stringy is part of normal fermentation. A sick kombucha does not look slimy or cloudy, it looks like the mould you would find on old bread, sitting in a dry patch above the liquid.
Colour is the second clue. Blue, green and black belong to mould. Cream, beige, tan and brown all belong to a healthy culture, including the darker patches that some people mistake for rot.
Six of these seven are questions of conditions, not of health. A culture in a cold room is slow, not sick. A culture with too little starter liquid is exposed, not sick. A culture that fermented for three weeks is vinegar, not sick. Calling all of that a sick kombucha is what makes people throw away perfectly good cultures.
| Mistake | What happens | How to avoid it |
|---|---|---|
| No starter liquid | pH stays high for days, mould gets a chance | always add 100 to 150 ml of finished kombucha |
| Tea still hot | above 30 C the culture is damaged immediately | cool to hand warm before the SCOBY goes in |
| Tight lid | the culture needs air in the first phase | cloth and a rubber band |
| Flavoured tea with oils | weakens the SCOBY over several batches | plain black or green tea |
| Too little sugar | the culture runs on its reserves | 70 to 90 g per litre |
| Metal vessel | prolonged contact harms the culture | glass or food grade plastic |
The first two account for most cases of genuine mould. Starter liquid is the cheapest insurance in fermentation. It drops the pH within minutes and closes the window in which a sick kombucha can develop.
| Room temperature | First fermentation | Second fermentation |
|---|---|---|
| 18 C | 7 to 10 days | 4 to 6 days |
| 22 C | 9 to 14 days | 3 to 4 days |
| 24 C | 7 to 10 days | 2 to 3 days |
| 28 C | 5 to 7 days | 1 to 2 days |
This table settles most worries on its own. A jar that has done nothing visible in five days at 18 C is exactly on schedule. Judging a culture by the calendar instead of the thermometer is the fastest way to diagnose a sick kombucha that does not exist.
Do not taste a batch with visible mould, and do not try to rinse the SCOBY and reuse it. This is the one situation in fermentation where there is no salvage operation worth attempting.
General household food hygiene guidance is published by the World Health Organization, and it applies to fermented drinks exactly as it does to everything else in a kitchen.
The single best protection against ever losing a culture is a second jar. It costs one batch of sweet tea and five minutes, and it means a mould incident is an inconvenience rather than a restart from scratch.
A hotel also solves the slow batch problem. If a jar is dragging in a cold month, adding a mature layer and a bigger dose of starter liquid from the hotel brings it back on schedule within one cycle.
These three come up again and again, and none of them is a problem. They deserve their own section because each one has been the reason someone threw away a healthy culture.
| What you see | What it actually is | Why it happens |
|---|---|---|
| A hole through the middle of the SCOBY | a growth irregularity | the new layer formed around a bubble |
| Dark brown or almost black patches on the disc | tea tannins staining the cellulose | stronger tea or longer batches |
| A jelly like blob hanging underneath | yeast colony | very active fermentation, often in warm weather |
All three are cosmetic. A SCOBY does not need to be a smooth white disc to work. Some of the most productive cultures look decidedly unattractive.
Taste problems are a separate category from a sick kombucha, and they almost always trace back to two variables you control.
| Taste | Cause | Adjustment |
|---|---|---|
| Too sweet | bottled too early | wait two to four more days, taste daily |
| Too sour | left several days too long | bottle earlier, or blend with fresh sweet tea |
| Flat | no second fermentation | 2 to 4 days in a sealed swing top bottle |
| Yeasty | warm room, very active yeasts | strain more thoroughly, ferment cooler |
| Thin, weak flavour | too little tea or sugar | 6 to 8 g tea, 80 g of sugar per litre |
| Metallic | prolonged metal contact | glass or food grade plastic only |
None of these six requires a new culture. Taste is a setting, not a verdict, and a batch you do not enjoy drinking still makes excellent starter liquid or salad vinegar.
Two questions arrive alongside almost every worry about a sick kombucha, and neither is about health of the culture. They are about the drink itself, and both have straightforward answers.
| Question | Answer | What changes it |
|---|---|---|
| How much alcohol? | traces, usually under 1 per cent | longer and warmer second fermentation raises it |
| How much sugar is left? | roughly 2 to 5 g per 100 ml | longer first fermentation lowers it |
| Is it caffeinated? | yes, part of the tea caffeine remains | green tea slightly less than black |
| Does it keep in the fridge? | two to four weeks | it keeps souring slowly, cold only slows it |
A batch that has gone very sour has simply travelled further down the second row. That is not a sick kombucha, it is a finished one, and it makes a better vinegar than most bottles sold as such.
Authorised health claims in the European Union are listed in the register kept by the European Food Safety Authority. We make no health claims on this page, and none of the advice above concerns anything other than the culture itself.
If you did lose a culture to mould, the restart takes fifteen minutes and one new SCOBY. Doing it properly the second time removes the cause rather than repeating it.
Follow those five steps and the risk of a sick kombucha drops to almost nothing. The acidity of the starter liquid closes the only window in which mould can establish itself.
Run through these five questions before concluding that you have a sick kombucha. In our experience they resolve the question in under a minute.
Four yes answers and one no to the first question mean the culture is healthy. That is the whole diagnosis.
| After | The SCOBY | The liquid |
|---|---|---|
| 1 batch | a thin new pale layer | sour, lightly cloudy |
| 3 batches | noticeably thicker, may be uneven | consistent timing |
| 6 batches | several fused layers | predictable, easy to judge |
| 12 batches | thick enough to split | unchanged |
| Any time | may darken or sink | may throw brown strings |
The last row is the one worth memorising. Darkening, sinking and stringy bits are what a mature culture does. None of them is a sick kombucha, and none of them needs any action beyond straining.
Live kombucha SCOBY
Shipped with its own starter liquid, ready for a first batch the day it arrives.
See the SCOBYThe full method: how to make kombucha. The comparison with kefir: kefir vs kombucha.
In almost every case you do not. A sick kombucha shows one thing only. A dry, fuzzy patch on the surface, blue, green or black. Brown strings, bumps, holes, a sinking SCOBY and a sour smell are all normal signs of an active culture.
No. Whether a SCOBY floats or sinks depends on how much gas it holds, not on how active it is. The reliable sign is a new pale layer forming on the surface within three to seven days.
Two usual reasons: not enough starter liquid at the start, or a room below 18 C. Add 150 ml of finished kombucha and move the jar to a spot between 22 and 24 C.
Those are yeast strands settling out. They are a sign of activity, not a problem. Strain them out when you bottle, or leave a few in as they help the next batch.
It is not sick, just fermented longer than you wanted. Keep 150 ml as starter liquid for the next batch and use the rest as a salad vinegar. Nothing needs to be thrown away.
No. If there is real mould, discard the liquid and the SCOBY, wash the jar thoroughly and start again with a fresh culture. Cutting away a patch does not remove what is in the liquid.
Almost always too little starter liquid, tea that was still hot when the SCOBY went in, or a jar sealed with a tight lid instead of a cloth. All three are easy to avoid.
Time and temperature. A slow batch in an 18 C room simply needs two more weeks. A sick kombucha has visible dry fuzz on the surface, and that does not appear from slowness.
