Water kefir
Milk kefir
Kombucha
Ginger beer
Kefir duo
Kefir and kombucha
Starter kit
RennetPour your strained water kefir into a swing-top bottle with a little fruit, juice or herbs, leave two or three fingers of air at the top and close it. After 24 to 48 hours on the worktop the drink is fizzy and has taken on the flavour of the fruit. Then the bottle goes into the fridge. On warm days, open it over the sink after one day to check the pressure.
What happens in the bottle
After the first fermentation, there is still a little sugar in your water kefir, and yeasts and bacteria are still swimming around in it, even with the grains taken out. Add fruit or juice and you give them fresh food. They make carbon dioxide again, but this time the bottle is closed. The gas has nowhere to go, so it dissolves into the drink. That is your fizz.
At the same time, the flavour of the fruit moves into the kefir. A few strawberries turn it pink and summery, rhubarb makes it crisp and tart, ginger gives it a kick. From one basic recipe you get a whole shelf of different drinks. How to make that base is in How to make water kefir.
Choosing the right bottle
For the second fermentation you need a bottle built to hold pressure. That matters more than it might seem.
| Bottle | Suitable? | Why |
|---|---|---|
| Thick glass swing-top, made for lemonade or beer | Yes, the best choice | Holds pressure well, the rubber seal closes tightly |
| Empty fizzy drink or sparkling water bottle with a screw cap | Yes | Designed for carbonated drinks |
| Small plastic sparkling water bottle | Yes, as a test bottle | You can feel the pressure by squeezing it |
| Decorative bottle, carafe, preserving jar | No | Thin glass or no real seal |
| Wine bottle with a cork | No | Not made for pressure |
Check the rubber seal on your swing-top now and then. If it has dried out or split, the gas leaks away and the drink stays flat. Spare seals cost very little and are easy to fit.
Step by step
1. Fruit into the bottle
Put the fruit, juice or herbs in the bottom of a clean swing-top bottle. Small pieces, so you can get them out again afterwards.
2. Kefir on top
Pour in the freshly strained water kefir through a funnel. Leave two or three fingers of space below the neck.
3. Close it
Snap the swing-top shut. Stand the bottle on the worktop at room temperature, out of the sun.
4. Wait
24 hours is enough for a fine fizz. If you want more sparkle, or your kitchen is cool, give it 48 hours.
5. Chill it
Then into the fridge for at least a few hours. Cold kefir holds its fizz better and foams less when you open it.
6. Strain and pour
Pour through a small sieve into the glass if you would rather not have bits of fruit in your drink.
How much fruit to add
You need less than you think. The fruit is mostly there for flavour and a little extra food. With too much, the drink quickly becomes very fizzy and a bit yeasty. These amounts are for a 1 litre bottle.
| Flavouring | Per litre | Taste |
|---|---|---|
| Strawberries | 4 or 5, cut into pieces | Summery, soft, pink |
| Raspberries or blackberries | A small handful | Deep red, lightly tart |
| Rhubarb | One stalk, chopped, with a teaspoon of sugar | Crisp, fresh, pink |
| Elderflower | Two or three flower heads, or a splash of elderflower cordial | Fragrant, summery |
| Fresh ginger with lemon | Two or three slices of ginger and a squeeze of lemon | Spicy and fresh |
| Apple juice with cinnamon | A good splash of juice and a piece of cinnamon stick | Rounded, autumnal |
| Orange | A few segments or a splash of juice | Sunny, slightly bitter |
| Mint and cucumber | A sprig of mint and a few slices | Cool, for summer |
If you use juice, choose pure juice with no sweeteners. Cordial works too, but keep it to a splash: it is very sweet and the bottle builds pressure fast. In September, a handful of blackberries from the hedgerow, rinsed well, turns the drink a deep purple and gives it a lovely wild sharpness.
Keeping the pressure under control
A second fermentation is not difficult, but a bottle under pressure deserves respect. A glass bottle left too long on a warm worktop with plenty of fruit in it can build up too much. A few habits keep it safe every time.
- Warm weather, shorter wait. At 25°C or more, 24 hours is often enough. Then straight into the fridge.
- Let some gas out. If in doubt, open the swing-top over the sink for a few seconds after one day and close it again.
- Do not overfill. The air at the top absorbs part of the pressure.
- Do not forget it. A bottle left four days on the worktop becomes far too lively. Set a reminder on your phone or stick a note on the fridge.
- Open it cold. A cold bottle foams much less than a warm one. Open it over the sink, with a tea towel over the top.
Recipes through the seasons
The second fermentation is where you follow the seasons. In April and May there is rhubarb in the garden or at the greengrocer's, in June the elder flowers in the hedgerows, summer brings strawberries, and once it turns cold you reach for ginger and lemon.
- Rhubarb water kefir: pink, tart, a bit like a rhubarb cordial with bubbles.
- Elderflower water kefir: fragrant and light, lovely as an alcohol-free aperitif in the garden.
- Strawberry water kefir: the summer classic, also great in a big jug at a barbecue.
- Lemon and ginger water kefir: for autumn and winter, fresh with a spicy edge.
- Water kefir ice lollies: for the hot days, when you have more bottles than you can drink.
If you want to go further with homemade sparkling drinks, there are more ideas in Homemade fermented lemonade.
When the bottle will not fizz
You did everything right, but nothing much happens when you open it. Usually it comes down to one of these:
| Cause | What helps |
|---|---|
| The rubber seal leaks | A new seal, or a different bottle |
| Too little food in the bottle | A bit more fruit, or a teaspoon of sugar |
| The kitchen is too cool | Give it 48 hours, or find a warmer spot |
| The base kefir was strained too early | A proper first fermentation first: the fig should float |
| The bottle is too full | Leave two or three fingers of air |
| The grains are still settling in | A few batches of patience |
More fixes for a flat drink, or one that is too sour, are in Water kefir problems and how to fix them.
Storing it after the second fermentation
In the fridge, your fizzy kefir is at its best for a few days. It slowly becomes drier and slightly more tart, and the fizz can still build a little, because fermentation carries on very slowly in the cold. So open the bottle now and then if it has been in there more than a week. Most people drink their bottles within a few days, and that is when they taste best.
Like every homemade fermented drink, water kefir contains traces of alcohol after a second fermentation, usually under 1%. Lots of fruit and a long time on the worktop push that up a little.
Frequently asked questions
Can I put the grains in the bottle too?
Can I skip the second fermentation?
Can I use frozen fruit?
How often can I reuse the same swing-top bottle?
Why does my bottle taste yeasty?
Just starting out? With 30 g of water kefir grains you make a litre a day for your bottles, and with 60 g two litres, enough for two flavours at once. They start at £11. The whole picture is in the complete water kefir guide.