blood heat 
noun [mass noun]
The normal body temperature of a healthy human being, about 37 °C or 98.4 °F.In the making of yoghurt the milk is kept at a temperature slightly above blood heat, the preferred conditions of the bacteria that bring about the fermentation....
- Beat the yoghurt in well, cover saucepan and place in a warm position to maintain blood heat.
- The water must not be allowed to boil and should only be hot, as chocolate melts at just above blood heat.