In both set of experiments, the fryer was filled with 4 l of
oil, which was preheated for 2 h prior to frying (Blumenthal,
1991) and discarded after 4 h. Temperature gradients
in the oil were minimized by means of a RW20 multi-speed
stirrer (IKA-Labortechnik, Germany) placed in the centre
of the oil bath.