Mechanisms Determining Crispness and Its Retention in Foods with a Dry Crust - Food Colloids: Self-Assembly and Material Science - page 495

34.4.5 Effect of Oil Presence after Deep Frying
A problem for the texture of deep-fried snack products with a crispy crust and a
soft interior is that often the crust rapidly loses its crispy character - typically
within 3-20 min after frying. In contrast, crispy loss is much slower for bread
with a crispy crust. In general, the decrease in crispness of the crispy crust is
attributed 1 to plasticizing of the solid matrix of the crust as the result of the
uptake of water transported from the moist inside to the crust or taken up from
the environment. However, this cannot explain the large difference in loss of
crispness between deep-fried products and baked products with a similar
overall structure. An important difference between the two types of products
is that, after frying, the adhering oil is sucked into the deep-fried products
during cooling down. 43
To study the possible role of the suction of oil into a dry crispy food, test
pieces of toasted rusk rolls ( 5 5 1 cm) were dipped for 5 s in hot (1801C)

or cold (351C) arichidonic oil. The fracture behaviour was studied by cutting at
a speed of 1 mm s 1 . Also the fracture behaviour was determined for model
deep-fried snack crusts (2.5 min in oil at 1801C) by wedge penetration at a speed
of 40 mm s 1 . From a portion of the snacks, the adhering oil was removed from
the sample as soon as possible after frying by wiping with tissue paper. 35
Measured force and sound pressure curves versus cutting time are shown in
Figure 5 for rusk rolls without oil and after dipping in cold oil. The force versus

B

Figure 5 A typical example of the force and sound pressure plotted against time for
cutting experiments on toasted rusk rolls without oil (left) and after dipping in
cold oil (right)