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Kombucha
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Starter kit
RennetKombucha turns too sour when it ferments too long, too warm or with too much starter liquid. You can still drink it: half and half with apple juice, topped up with sparkling water, or bottled with sweet fruit for a second fermentation. Very sour kombucha is also a strong starter liquid and a mild vinegar for dressings. Next time, start tasting on day 7, a day or two earlier in summer, and stick to one cup of starter per litre.
Why kombucha turns sour
Sourness in kombucha is not a fault; it is the whole idea. The yeasts break down the sugar in the tea and the bacteria turn the result into mild acids. The longer that carries on, the less sugar is left and the sharper the drink. At some point the balance tips from fresh and tangy to vinegar.
Where that point lies is a matter of taste, usually somewhere between day 7 and day 10. A few things bring it forward considerably.
The most common causes
| Cause | How you notice | What helps |
|---|---|---|
| Left too long | Hardly any sweetness, a sharp vinegar smell | Taste every day from day 7 |
| Too warm a spot | Sour after only a few days in summer | A cooler spot, at the lower end of 20 to 25°C |
| Too much starter liquid | The new tea is already quite sour on day one | Stick to one cup, about 250 ml, per litre |
| A very thick SCOBY for little tea | Each batch is ready sooner than the last | Peel off layers, move the rest to the SCOBY hotel |
| Starter taken from the hotel | The first litre after a break is extremely sour | Taste that batch extra early |
Most of the time it is simply warmth. At 25°C the culture works much faster than at 20°C. A batch that needs ten days in February can be past its best after five or six in July, and during one of our rare heatwaves, when an upstairs room easily reaches 27°C, it races along.
How sour is too sour?
"Too sour" depends on what you plan to do with the kombucha. Each use has its own ideal moment:
| For | Ideal taste |
|---|---|
| Drinking plain | Fresh and sharp with a clear touch of sweetness, like a tart lemonade |
| A second fermentation with fruit | A little less sweet, since the fruit brings new sugar |
| Half and half with apple juice | Can be properly sour; the juice balances it |
| Starter for the next litre | The sourer, the better protected the new tea |
| Dressings and quick pickles | Clearly vinegary, hardly sweet |
Keep that in mind and you never throw a drop away. If your kombucha has gone too far for one use, it usually fits the next one perfectly. Plenty of brewers deliberately bottle most of a batch early for drinking and let a small remainder run on, for starter and kitchen vinegar.
How to drink it anyway
Too-sour kombucha does not have to go down the sink. A few simple tricks make it pleasant again, sometimes nicer than planned.
- With apple juice. Half kombucha, half cloudy apple juice and a few ice cubes. It tastes like a lively, sparkling apple spritz. Grape juice or blackcurrant juice also work well.
- In a second fermentation. Put sweet fruit in the bottle, such as ripe pear, mango, pineapple or a splash of juice. Its sugar brings back some roundness and the yeasts add the fizz. How it works is in Kombucha: the second fermentation.
- With cordial. A spoonful of elderflower or raspberry cordial in the glass, the way you would make squash, and the sharpness is back in balance.
- Diluted. If it is only the strength that is too much, top it up with sparkling water. A slice of lemon and you have a light summer drink.
What to cook with it
Very sour kombucha is, in effect, a mild, fruity vinegar, and it earns its place in the kitchen.
- Dressing: kombucha, mustard, a little honey, oil, salt and pepper. The exact recipe is the kombucha vinaigrette.
- Quick pickles: thin slices of cucumber, red onion or radish with a pinch of salt and sugar, covered in kombucha and left overnight in the fridge. Lovely in a sandwich or with a burger.
- Marinade: a splash in the marinade for vegetables or chicken before they go on the grill.
- Proper vinegar: leave it even longer and it becomes kombucha vinegar. How, in Kombucha vinegar.
And of course, too-sour kombucha is the best starter liquid you could ask for. A cup of it gives every new litre a strong, safe start.
Getting it right next time
1. Taste sooner
A sip every day from day 7, and a day or two earlier in summer. A straw slipped down the side of the jar makes it easy.
2. Measure the starter
One cup, about 250 ml, per litre. Do not pour by eye: measure it once, then always use the same cup.
3. Keep the SCOBY slim
If your SCOBY has grown thicker than one or two layers, peel off the oldest and move them to the SCOBY hotel.
4. Rather a little early
A trace of sweetness is good. It disappears in the second fermentation anyway, and the kombucha gets a little drier in the fridge over time.
The basic recipe with every quantity is in How to make kombucha.
And if it stays too sweet?
The opposite happens too, mainly in winter: after ten days your kombucha still tastes like sweet tea. It is nearly always too cold. Move the jar somewhere warmer, a shelf in the airing cupboard (away from the hot water tank) or a room where the central heating stays on, and give it a few extra days. Check too that you used a full cup of starter liquid. More on fermenting at low temperatures is in Fermenting in winter.
Keep a little log
The easiest answer to sour kombucha is a scrap of paper. Stick a note on the jar or keep a notebook in the kitchen drawer, and write down four things for every batch: the date, the tea, the temperature in the kitchen and the day it tasted best. After three or four batches you will see your own pattern. In summer it may be day 6, in winter day 11. Then you know exactly when to start tasting, and the guesswork is over.
Frequently asked questions
Can I still drink kombucha that is too sour?
Can I just add sugar to the jar?
Does the fridge stop it getting more sour?
Has my SCOBY been harmed by a sour batch?
No SCOBY of your own to experiment with yet? Our live kombucha SCOBY with starter liquid costs £16 and is ready for your first batch. Standard tracked delivery across the UK is £4.90, free from £35, and all prices include VAT. Everything about kombucha is on the kombucha page.