3. Mechanical testing
In order to characterise the texture of cooked patties,
the mechanical properties of the cooked patties were
determined using a compression test. The schematic
illustration of the compression test is illustrated in Fig. 3.
After the hamburger patties were removed from the
grill, the compression tests were performed using an
Instron testing machine (Instron 5567, UK) attached to
a 200 N load cell. Since the mechanical properties of the
hamburger patties were influenced by the speed of crosshead,
the compression tests were performed at a constant
cross-head speed of 1 mm/min. Two aluminum
plates with a diameter of 25 mm were used. Four cylindrical
samples with a diameter slightly larger than 25
mm were cut out from each patty (see Fig. 3). The
hamburger samples were compressed up to 50% of their
original height (approximately 5 mm) at a constant
speed and then unloaded at the same speed. Loading
and unloading curves were recorded for each compression
test. A curve fitting procedure was applied to both
the loading and unloading curves in order to analyze the
Fig. 1. Schematic illustration of the cooking apparatus. compression results. A typical compression test result