The freezing temperature for both fast and slow conditions was monitored using an Agilent HP 75000 Series C Data Acquisition & Control unit (Agilent Technologies Ltd, Engle-wood, CO, USA), which was fitted with T-type thermocouples mounted in sets of 4 on thin nylon rods — 3 placed within 5 mm of each other to ensure a centre reading temperature, and a 4th inserted just under the sample surface to monitor the surface temperature set and set to record data at 1 min intervals.