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 80.degree. C. in no more than 30 minutes in the heating stage. The heating rate is at least 0.5.degree. C./minute and during cooling is at least -0.5.degree. C./minute. The plateau maximum temperature is from 70 to 85.degree. C. By plotting the pasteurisation protocol on a time (t, minutes) versus temperature (T, .degree. C.) graph, one obtains a trapezium having an area less than 13,000.degree. 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.