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Chapter 23 Separation Techniques: Mechanical and Chemical Methods
pressure than water. This causes the alcohol to change
from a liquid to a gas state before the water does. The
gaseous alcohol is collected in a closed system and
condensed back into a liquid.
The oil used to make margarine often contains
compounds that can cause unpleasant odors. Steam
distillation is often used to remove these compounds
from the oils before they are solidifi ed and made
into margarine.
In each of these examples, a compound is separated
from a food mixture. This separation is possible
because different parts of the mixture have different
boiling points.
Selective Separation Through Barriers
Some food components are separated by passing
the food through barriers. A barrier lets some particles
pass through while trapping others. Screens are widely
used as barriers in the food industry to sift and sort
foods. Filter paper and semipermeable membranes are often used as
barriers, too. These barriers are used for the processes of fi ltration,
osmosis, and reverse osmosis.
Filtration
Filtration uses porous paper
to let liquids and small solutes
pass through while trapping
aggregates (clusters of precipitate).
Drip coffeemakers use this type
of barrier system. Paper coffee
fi lters let the dissolved fl avor
compounds and hot water pass
through while trapping coffee
grounds. Filter papers need to be
sanitary and taste-free.
The food and beverage
industries often use fi ltration
to remove visible solids from
solutions, 23-6. You just read
that fi ltration is used to remove
precipitates of caffeine and tannins
from tea concentrate. Filtration
is also used to remove organic
matter from liquids. Fruit juice
manufacturers use fi ltration in this
way to make pulp-free fruit juice.
© Patricia Hofmeester/Shutterstock
23-6 The solid portions of grapes are fi ltered out during the wine-making
process.
cooling fan
condensation
tubes
activated
carbon
distilled water
steam
boiling water
heater
waste gases
Water Distiller
Goodheart-Willcox Publisher
23-5 This diagram shows how a countertop
appliance distills water for home use.