The present invention describes an improved pasteurisation protocol for pasteurising microbial cells is disclosed. The protocol has three stages, a first heating stage, a second plateau stage at which the cells are held at a (maximum and) constant temperature, and a third cooling stage. Both the heating and the cooling stages are rapid, with the temperature of the cells passing through 40 to 70°C in no more than 30 minutes in the heating stage. The heating rate is at least 0.5°C/minute and during cooling is at least -0.5°C/minute. The plateau maximum temperature is from 70 to 85°C. By plotting the pasteurisation protocol on a time (t, minutes) versus temperature (T, °C) graph, one obtains a trapezium having an area less than 13,000°C. minute. Not only does this result in a smaller energy input (and so a reduction in costs), but a better quality (and less oxidised) oil results having a peroxide value (POV) of less than 1.5 and an anisidine value (AnV) of less than 1.0.
