709
Chapter 23 Separation Techniques: Mechanical and Chemical Methods
Solvents are also used to remove unwanted food components.
An example is caffeine in coffee and tea. Caffeine is a mild stimulant
that some people wish to avoid. One method for removing caffeine
from coffee beans uses water as a solvent. Caffeine dissolves in water,
but so do many of the fl avor compounds found in coffee beans. To
remove the caffeine without reducing the fl avor of the coffee, green
coffee beans are soaked in water. This produces a solution that is
saturated with caffeine and fl avor compounds. The green, soaked
beans are discarded. Then the solution is passed through carbon
fi lters. The caffeine is attracted to the carbon, but the fl avor compounds
are not. Therefore, the fi ltered solution is caffeine free but still saturated
with fl avor compounds.
Next, premium coffee beans are soaked in the fi ltered solution.
Because the solution is saturated with fl avor compounds, the fl avor
from this second batch of beans stays in the beans. However, because
the solution has little or no caffeine remaining, it will dissolve the
caffeine from the beans. These beans are then dried and roasted. The
end product is coffee beans that are 99.9% caffeine free. See 23-4.
Other solvents used to extract caffeine include methylene chloride,
ethyl acetate (a compound found in many fruits and vegetables), and
carbon dioxide.
Crystallization
Crystallization is a process
that separates the solute from
the solvent in a supersaturated
solution. The atoms of the solute
become arranged in a repeating
order to form crystals. This
happens when water evaporates
from salt- and sugar-based
solutions. The solute will begin to
crystallize. It will settle out of the
solution as soon as the saturation
point is passed. The solvent does
not need to completely evaporate
in order to collect the crystals.
The crystals can be removed from
the solution by centrifuging.
Crystallization is the process
used to make rock candy. Crystals
form from a supersaturated sugar
solution as it cools. The crystals
keep forming for a few days at
room temperature as water
evaporates from the solution.
© iwka/Shutterstock
23-4 Decaffeinated coffee is made by extracting the caffeine from green
beans while leaving behind the majority of the fl avor compounds. The
fi nal product looks very much like caffeinated beans.