Can I leave the kefir on the bench - even if that means it doesn't necessarily stay between 25°C - 36°C ?

Kefir is a colony of living microbes. Heating them above 38°C will cause heat stress and damage and by 40°C, your culture is dying. If your milk falls below 25°C your kefir culture will be too cold for optimal growth and will take longer to become delicious and may even stop growing altogether.

Keeping the kefir on the kitchen counter, or in another warm spot, is sufficient most of the year. If the kefir is not working or taking too long to ferment we recommend using an aquarium heater in water surrounding the kefir jar. This heats your kefir. Most aquarium heaters are adjustable and can be set between 25°C - 37°C.