2. Cooking experiment
The two cooking methods compared in this paper are
the conventional cooking and the combined cooking of
hamburger patties using domestic sandwich plate grill
(Breville, SG600B). Conventional cooking is done by
placing the frozen raw meat patties between the heated
plates of the grill for predetermined time. Combined
cooking, on the other hand, is done by applying a
voltage of 50 V of alternating current across the two
heated surfaces, utilising the principles of ohmic heating
together with the plate heating. An isolating transformer
was used to provide safe working environment. A variac
was used to adjust the voltage supplied to the grill, while
current and voltmeters where used to measure the
voltage and current passing through the meat patties.
The voltage was remained constant at 50 V while the
current starts from zero initially and goes up to 13 A as
the meat thaw. At the end of the cooking the current
drops automatically to zero due to the loss of moisture,
which caused the meat to be non-conductive. The current
was recorded continuously in a computer using Pico
data logger. The surface and center temperature of the
meat patties were measured during the cooking using
thermocouples and were recorded together with the
current using the Pico logger (see Fig. 1). It was very
difficult to insert the thermocouple in the meat patties so
that it is positioned halfway through its thickness.
The grill was switched on for sufficient time for its
two plate to reach the set temperature of close to 180 C,
before the frozen burger was sandwiched between the
two hot plates. The upper and lower plates of the grill
were cleaned with detergent after each run to have reproducible
results. The center temperature profiles of
the meat patties prepared using both cooking techniques
are illustrated in Fig. 2. Pan et al. (2000) suggested that
meat patties have to be cooked until its centre temperature
reaches 70 C and should be held for 15 s following
that. Using this criterion, the required cooking
was determined as 117 and 163 s for the combined and
conventional techniques, respectively.
After determining the required cooking time for both
cooking methods, the cooked patties were characterised
by measuring their mechanical properties and composition
(fat, moisture, and solid content).