Water kefir
Milk kefir
Kombucha
Ginger beer
Kefir duo
Kefir and kombucha
Starter kit
RennetWater kefir, milk kefir, kombucha and ginger beer all work best at 20 to 25°C. In a winter kitchen at around 16 to 18°C, especially once the heating goes off at night, everything slows down: allow a few extra hours for a kefir batch, a few extra days for kombucha and an extra day for ginger beer. Find a steadier spot (a shelf next to the airing cupboard, not inside it, or a high shelf in a heated room), keep the jar off the radiator and away from cold, wet windows, taste rather than watch the clock and keep the quantities of the basic recipe.
What does the cold do to your cultures?
It slows them down without killing them. The yeasts and bacteria just work more gently.
At 18°C the fig in your water kefir is often still sitting on the bottom after 24 hours, and the drink is distinctly sweet. Milk kefir stays runny and still smells of milk. Kombucha, after ten days, can taste like a slightly sweet iced tea. The ginger beer plant gives a flat, sugary jar where you expected a lively one. These are not failed batches: they are just not finished yet. The next day the result is often quite different.
When the room drops well below 15°C, fermentation all but stops. That is the moment to move the jar, because the flavour can change too, becoming duller and more yeasty.
The heating timer: the real winter problem
In most British homes it is not the average temperature that catches people out, it is the swing. The central heating comes on at six, goes off at half eight, comes back for the evening and switches off again at bedtime. A kitchen can sit at 21°C at teatime and 14°C by four in the morning.
Your cultures cope with that, but they lose time every night. Two simple fixes: put the jar somewhere that holds its warmth (an inside wall, a high shelf in a heated room), and wrap it. A thick towel around the jar or an insulated cool bag keeps the warmth of the evening in until the heating comes back on. Leave the top uncovered under its tea towel so the culture can breathe.
The airing cupboard: next to it, not in it
If your home still has a hot water cylinder, the airing cupboard is often the warmest spot in the house. But right beside the tank, or after the immersion or the boiler has been running for an hour, it can climb well past 25°C, and your water kefir turns sharp in half a day while kombucha goes vinegary.
The better trick is to use the warmth that leaks out. A shelf on the landing just outside the airing cupboard, or the top of a chest of drawers against its wall, often sits a steady few degrees above the rest of the house. Leave a small thermometer there for a day and check it morning and evening. If the reading sits between 20 and 25°C, you have found your winter spot. Homes with a combi boiler and no cylinder have no airing cupboard at all, so go for the warmest room instead.
Other places to put the jar
Anywhere that stays as steady as possible between 20 and 25°C, day and night.
| Spot | Good idea? | Why |
|---|---|---|
| Windowsill | No | Cold glass, condensation and draughts at night |
| On the radiator | No | Far too hot, and very uneven |
| Near a radiator, not touching | Yes | Gentle warmth while the heating is on, worth checking with a thermometer |
| Top of a dresser or a high shelf | Yes | Warm air rises: often a few degrees more than the worktop |
| On top of the fridge | Often | The back of the appliance gives off a little heat |
| Inside the airing cupboard | Rarely | Often well over 25°C near the cylinder |
| Utility room, conservatory, garage | No | Far too cold in winter |
Condensation, damp and mould
A cool house is fine for fermentation, but winter condensation calls for a little extra care. Mould likes still air, wet surfaces and damp fabric, and a kitchen with the kettle on and the windows streaming has all three.
- Keep the cloth dry: if the tea towel over the jar gets damp from steam or a splash, swap it for a clean, dry one.
- Keep away from cold walls and windows: a jar pushed against an outside wall or into a corner that gets black spots in winter is in the wrong place.
- Do not stretch the times endlessly: a slow batch is fine, but a jar left for days on end without enough acidity gives mould a chance. Move it somewhere warmer rather than just waiting.
- Kombucha needs its starter liquid: a full cup of starter (about 250 ml) per litre makes the tea sour enough from the start to keep mould away, which matters even more in the cold.
New growth or something to worry about on your SCOBY? See Kombucha: mould or normal?
How to adjust the timings
Leave the quantities alone. Just give the batch more time and taste more often.
- Water kefir: 30 g of grains, 1 litre of water, about 60 g of sugar, a dried fig and a slice of lemon, as always. Wait until the fig floats and the drink is only slightly sweet: in winter that can take a few extra hours, sometimes half a day. In the bottle, the second fermentation needs closer to 48 hours than 24. Use water at room temperature, never hot. The basic recipe is in How to make water kefir.
- Milk kefir: 20 g of grains to 1 litre of whole milk. Take the milk out of the fridge a while beforehand, and if it is still runny after 24 hours, give it a few more hours and swirl the jar gently. Everything about texture is in Milk kefir too thin or too thick.
- Kombucha: 1 SCOBY, about 250 ml of starter liquid, 80 g of sugar and 3 tea bags per litre. Start tasting towards the end of the 7 to 10 days, or a little after, and plan on 5 days rather than 2 in the bottle. The method is in How to make kombucha.
- Ginger beer: 20 g of ginger beer plant, 1 litre of water, 60 g of sugar, 2 slices of fresh ginger and a dried fig. Give the jar the full 48 hours, and the closed bottle a day more than in summer. Everything is in How to make ginger beer.
Just arrived? First batches are always slower, and winter stretches that settling-in time: see Water kefir: the first days.
Flavours for the cold months
Summer has strawberries and elderflower; winter has citrus, apples and spice. A few segments of clementine and a thin slice of ginger give water kefir a bright freshness, and the lemon and ginger water kefir livens up a grey afternoon. For kombucha, a Bramley apple and a cinnamon stick work wonders, as in the apple and cinnamon kombucha. And for anyone skipping the wine on New Year's Eve, a well-chilled lemon ginger ale fizzes nicely in a glass.
In the cold, fruit ferments more slowly in the bottle. In winter that is actually a bonus: less chance of a bottle gushing over when you open it.
Taking a break over Christmas
Then the cold works in your favour. Water kefir grains will wait up to two weeks in the fridge in fresh sugar water (renewed after a week), milk kefir grains a weekend in fresh milk with the lid on. The SCOBY stays at room temperature in its jar of sweet tea for two or three weeks, or joins your spare layers in a SCOBY hotel. After the holidays, one or two normal batches and everything is back on track.
Is winter a good time to start?
Yes. The evenings are long, you are at home more and you get to know your culture without any rush. Start in January and by spring you will have grains in fine form, ready for a rhubarb water kefir when the first stalks come up on the allotment.
Frequently asked questions
At what temperature does kefir stop fermenting?
Should I add more sugar when it is cold?
Can I keep my jar in the airing cupboard?
Can I put the jar on a radiator?
Do I need a heat mat?
Fancy getting through the winter with three homemade drinks? The fermentation starter kit brings together water kefir, milk kefir and kombucha for £40, a saving of £7 compared with buying them separately. For two, the water kefir and kombucha set saves £4.