Most home ferments are happiest between 20 and 29°C, so a Pakistani summer speeds everything up and a cold snap slows it down. In summer, use less culture, choose the coolest room and taste early. In winter, keep the jar somewhere warm and be patient.
Season by season
| Ferment | In very hot weather | In cold weather |
|---|---|---|
| Milk kefir | Use fewer grains, toward 1 teaspoon for a litre of milk. Choose the coolest room and start checking at 6 to 8 hours. It can be ready in under 12 hours. | Keep the jar warm. In winter you can use up to 1 tablespoon of grains for every 500ml of milk. A batch may need closer to 24 to 48 hours. |
| Water kefir | 24 hours or less is plenty. Do not go beyond 48 hours, or the grains run out of food. | Allow up to 48 hours in a warm spot. |
| Kombucha | Keep it at 20 to 29°C. Never add the SCOBY to tea above 35°C. Taste from day 5. Keep the second ferment to 12 to 24 hours, and open the caps daily. | It slows down. Expect the longer end of 7 to 14 days, and keep the jar warm. |
| Sauerkraut | It goes soft above 24°C. Make it between November and March, or in an air-conditioned room. | At 21 to 24°C it takes 3 to 4 weeks. At 15 to 18°C it takes 5 to 6 weeks. |
| Kimchi | Ferment it in the fridge for 3 to 4 days. | Leave it 1 to 2 days at a steady 20°C, tasting daily, then refrigerate. |
| Gajar ki kanji | It can be ready in 1 to 2 days, so taste daily. | It usually takes 5 to 7 days. |
| Beet kvass | Ready in 2 to 4 days. | Allow 4 to 7 days. |
Why temperature matters
Fermentation is living microbes at work, and warmth speeds them up. Too hot, and a batch races past its best: milk kefir turns sour or splits into curds and whey, sauerkraut goes soft, and kombucha turns sharply sour. Too cold, and nothing seems to happen. A cheap kitchen thermometer, left beside the jar, tells you more than guessing.
Ten rules for hot weather
- Keep ferments at 20 to 29°C wherever you can. Use the coolest room, an air-conditioned room, or a cupboard away from the stove.
- Keep jars out of direct sun and away from windows.
- Use fewer grains or less starter, and taste earlier than the usual time.
- Strain milk kefir as soon as it thickens. Do not wait for the full day.
- Make kimchi in the fridge, and make sauerkraut in the cooler months.
- Keep second ferments short, 12 to 24 hours, and open the caps every day to let the gas out.
- Chill finished drinks as soon as they are fizzy, and open them slowly over the sink.
- Wash your hands and equipment: warm kitchens grow unwanted microbes faster.
- Cover jars with a tight-weave cloth or coffee filter and a rubber band, to keep insects out.
- Throw away anything with fuzzy mould or a rotten smell. Heat makes this more likely.
Ten rules for cold weather
- Move jars somewhere warmer, but not onto a heater or into direct sun.
- Wrap the jar in a towel to hold the warmth, and keep it away from draughts.
- Give each batch longer, and judge it by taste and smell, not the clock.
- Use a little more grain for milk kefir, up to 1 tablespoon for every 500ml.
- Never add a SCOBY to tea warmer than 35°C. Cool the tea first, even when the room is cold.
- For sauerkraut, expect 5 to 6 weeks at 15 to 18°C, and check it for scum two or three times a week.
- Be patient with new grains: they are slower to wake in cold rooms.
- Keep your starter safe: a spare SCOBY should stay at room temperature, not in the fridge.
- If a batch is very slow, check the thermometer before changing anything else.
- Store grains in the fridge only when you are taking a break.
The methods themselves are in our guides: milk kefir, water kefir, kombucha, sauerkraut and kimchi, and kanji and kvass.
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Sources: Cultures for Health, Milk kefir: temperature and culturing time, and University of Georgia, National Center for Home Food Preservation, Kombucha tea, both opened 10 October 2026; the timings for sauerkraut, kimchi, kanji and kvass are from our own guides, which we checked against university extension services. Written by KefirBuy.
