The processing of oils is vital to their ultimate use within the food industry. Control over the physical properties of such materials could be achieved through the application of high-intensity ultrasound (HIU). However, the exact mechanism, centred upon acoustic cavitation, is currently unclear. To investigate the cavitation environment in oils further, the ring-up of a HIU source in an oil media is studied in the presence and absence of a pre-existing bubble population. High-speed imaging and acoustic measurements within the system is demonstrated to be extremely useful in characterising the dynamics present under non steady-state conditions. The behaviour of the clusters generated in the first 1000 ms under these conditions is shown to be significantly different depending on the bubble population. A bifurcated streamer (BiS), originating from a unique bi-cluster event, is only observable in the presence of a bubble population during the ring-up process to higher cluster orders. In addition, the lifetime of this BiS event is highly temperature dependent and is shown to be a good marker for the viscosity of the oil employed.