2. Parts of an evaporator
• Heat exchanger (k/a calandria): transfers
heat from steam to the food
• Means of separating the vapors produced
• Vacuum pump: Mechanical or steam
ejector
3. Selection criteria
• Operating capacity
• Degree of concentration required
• Heat sensitivity of product
• Requirement for facilities to recover
volatiles
• Ease of cleaning
• Reliability and simplicity of operation
• Size of evaporator
• Capital and operating costs
11. Climbing-film evaporator
• Thin film of liquor is forced up the evaporator tubes
• For low-viscosity foods (for example milk)
12. Falling-film evaporator
• Feed is introduced at the top of the tube bundle
• For more viscous foods
• For heat sensitive foods: yeast extracts, fruit juices
16. Expanding-flow evaporator
• Uses similar principles to the plate evaporator but has a
stack of inverted cones instead of a series of plates.
• The vapor-concentrate mixture leaves the cone assembly
tangentially.
ADVANTGES
• Compactness
• short residence times
• high degree of flexibility achieved by changing the number
of cones.
18. Effect on foods
Aroma compounds that are more volatile than
water are lost during evaporation.
• This reduces the sensory characteristics of most
concentrates
• In fruit juices this results in a loss of flavor
• In some foods the loss of unpleasant volatiles
improves the product quality (for example in
cocoa)
19. Evaporation darkens the color of foods
Because of:
• increase in concentration of solids
• reduction in water activity
Other changes
• Vitamins A and D and niacin are unaffected.
• Additional vitamin losses occur during storage
20. Distillation
• When a food that contains components having
different degrees of volatility is heated, those that
have a higher vapor pressure (more volatile
components) are separated first.
• Distillate: components that are separated first and
are more volatile
• Bottoms or residues: components that have a
lower volatility
21. • Feed liquor flows continuously through the column.
• As it is heated, volatiles are produced and separated at
the top of the column as distillate.
• The residue is separated at the base.
• In order to enhance the separation of these components,
a proportion of the distillate is added back to the top of
the column (reflux) and a portion of the bottoms is
vaporized in a reboiler and added to the bottom of the
column.
• Columns are filled with either a packing material
(typically ceramic, plastic or metal rings) or fitted with
perforated trays, both of which increase the contact
between liquid and vapor phases.
