How temperature affects fermentation
Temperature is a key part of making milk kefir. Kefir grains contain a community of bacteria and yeasts, and lactose in milk provides food for fermentation. This process gives milk kefir its distinctive tangy flavour.
Different bacteria favour different temperatures. At 20–30°C, the bacteria in kefir are active, converting lactose into lactic acid as the milk thickens and develops its flavour. Fermentation slows in cooler conditions. At 35°C or above, the grains die.
Grain-to-milk ratios at different temperatures
The ratio also matters. The best starting point depends on the type and brand of milk, your preferred taste and the room temperature.
| Room temperature | Grains : milk | What changes |
|---|---|---|
| Below 20°C | 1 : 10 | Activity and fermentation slow in cool conditions, so use more grains relative to the milk. |
| 20–30°C | 1 : 20 | This starting ratio produces thicker milk kefir with a slightly sour taste. |
| Above 30°C | 1 : 30 | Fermentation speeds up in warm conditions. Use more milk relative to the grains to help prevent the kefir becoming too sour. |
These are rough starting points. The ratio that suits you depends on your preferences and the milk you use. Try different ratios to find one that works for your conditions.
Refrigerate milk kefir after fermentation
The microorganisms continue growing and fermenting after the milk kefir is ready, so its flavour and texture can keep changing. Refrigerate finished milk kefir below 4°C to help prevent it becoming too sour or spoiling. Do not freeze it.
Temperature affects the fermentation rate, the microorganisms in milk kefir and its shelf life. Take time to find the fermentation conditions that suit your taste.
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