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Unit 7 Working with Complex Food Systems
is what makes it necessary to hold on when riding a merry-go-round.
An object that is rapidly moving around a central point will move in
a straight line when it is released.
A cotton candy machine makes use of this principle. A hot sugar
syrup is held in a central tub with very tiny holes in the outside
surface. This tub spins inside a large collection tub. As the central
tub spins, the hot syrup is forced through the tiny holes and out into
the collection tub. The contact with cool air immediately solidifi es
the syrup into soft, pliable threads, which are wrapped around a
paper cone.
The food industry uses centrifugal force in a separation process
called centrifuging. This process separates particles of different densities.
It works on the principle that density affects the speed at which matter
moves outward from a center of rotation. Dense objects and fl uids
will move faster than those that are less dense. Centrifuging is done
using a machine called a centrifuge. Centrifuges are used to separate
cream from milk and oil from water. These fl uids are placed in a
drum in the centrifuge. The drum spins around a central axis at
high speeds. As the drum spins, the denser, water-based particles
move out of the drum through small holes on the outside wall. The
less-dense cream or oil stays closer to the center and is removed
through a pipe.
Pressure
Another use of force to separate foods is in the use of presses.
Presses apply extreme pressure to products to squeeze out desired
components. Presses work well with foods that have a high moisture
or fat content. Molasses is extracted
from sorghum and sugar cane
with presses.
Pressure can be combined
with movement to speed separation.
This principle is demonstrated
in the way a juicer works. The
pressure of pushing a lemon down
on a juicer is not enough to remove
the maximum amount of juice. By
adding a twisting motion against
the ridged surface of the juicer, more
juice is released. This technique
is similar to the commercial
process used to extract orange and
grapefruit juices. See 23-3.
Pressure is used to prepare
some foods for separation. For
instance, before the parts of grain
kernels can be separated, the
grain needs to be ground. The
© Thomas Oswald/Shutterstock
23-3 Squeezing juice from fruit is one example of separation by pressure.
Here, apple juice is shown being made from a traditional apple press.