A pasteurisation protocol for pasteurising microbial cells is disclosed. The protocol has a heating stage, a plateau stage at which the cells are held at a (maximum and) constant temperature, and a cooling stage. The heating and cooling stages are rapid, the temperature of the cells passing through 40 to 80° 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. This results in a smaller energy input (so a reduction in costs) and a better quality (and less oxidised) oil having a peroxide value (POV) of less than 1.5 and an anisidine value (AnV) of less than 1.0.
