its a presentation based on conventional food processing techniques and it contains drying methods also along with freeze drying and concentration and evaporation.

1. CONVENTIONAL FOOD
PROCESSING
TECHNIQUES
DRYING , CONCENTRATION AND
EVAPORATION.
UMA BANSAL
M.Tech. (food technology)

2. CONTENTS
 DRYING
 PURPOSES OF DRYING
 TYPES OF DRYING
 TYPES OF DRYERS
I. TRAY DRYER
II. DRUM DRYER
III. FREEZE DRYER
 CONCENTRATION
 BENEFITS

3. CONTENTS
 METHODS OF CONCENTRATION
I. SOLAR CONCENTRATION
II. OPEN CATTLES
III. FLASH EVAPORATORS
IV. THERMAL CONCENTRATION
V. FREEZE CONCENTRATION
 EVAPORATION
 USES OF EVAPORATION
 TYPES OF EVAPORATION
I. OPEN KETTLE OR PAN EVAPORATION
II. HORIZONATAL TUBE NATURAL CIRCULAR
EVAPORATOR
III. VERTICAL TUBE NATURAL CIRCULAR
EVAPORATOR
IV. FORCE CURCULATION TYPE EVAPORATOR

4. DRYING
 Food drying is one of the oldest methods of preserving
food.
 drying reduces the moisture in foods making them
lightweight and convenient to store, it can easily be used
in place of other food preservation techniques.
 one can even use drying along with other food
preservation techniques such as freezing or canning,
which would make the process of food preservation
even better.
 Drying food is simple, safe and easy to learn.
 dried foods are good sources of quick energy and
wholesome nutrition, since the only thing lost during
preservation is moisture.

5. DRYING
Thermal drying:
Drying commonly describes the
process of thermally removing volatile
substances (moisture) to yield a solid
product.
Non-thermal drying
1. As Squeezing wetted sponge
2. Adsorption by desiccant (desiccation)
3. Extraction.

6. PURPOSES OF DRYING
In food technology, drying is carried out for one or more
of the following reasons:
1. To avoid or eliminate moisture which may lead to
corrosion and decrease the product stability.
2. To improve or keep the good properties of a material,
e.g. flow ability, compressibility.
3. To reduce the cost of transportation of large volume
materials ( liquids)
4. To make the material easy or more suitable for
handling.
5. Preservative.
6. The final step in: Evaporation, Filtration,
Crystallization

7. TYPES OF DRYING
1. Direct :Convective Drying
Drying is established through direct contact between the
product and the gas heating medium .Material reaches
steady state temperature near gas wet temperature
2. Indirect Drying:
Established from heated surface in contact with the product.
The heating medium and product are separated by wall.
Material reaches steady state temperature near liquid
boiling point for contact rate drying .
3. Radiation :
Heat transfer establishes by radiation from energy source.
This is no contact from heated surface or medium and
product

8. Types of dryers
1. Tray dryer
2. Drum dryer
3. Freeze dryer

9. TRAY DRYER
These types of dryers use trays or similar product
holders to expose the product to heated air in an
enclosed space.

10. ADVANTAGES OF TRAY DRYING
1. Simple in handling
2. Lesser capital cost
DISADVANTAGES
1. Non-uniform drying of a product at different
locations within the system.
2. Time required for drying is more
3. The major disadvantages of this type of dryers
are the high labor cost involved during the
loading and unloading of the drying materials
and the low capacities of the units.

11. DRUM DRYER
It consists of a drum of about 0.75-1.5 m in diameter
and 2-4 m in length, heated internally, usually by
steam, and rotated on its longitudinal axis.

12. ADVANTAGES OF THE DRUM
DRYER
1. The method gives rapid drying, the thin film spread over a large area resulting
in rapid heat and mass transfer.
2. The equipment is compact, occupying much less space than other dryers.
3. Heating time is short, being only a few seconds.
4. The drum can be enclosed in a vacuum jacket, enabling the temperature of
drying to be reduced.
5. The product is obtained in flake form, which is convenient for many purposes.
DISADVANTAGES
1. Operating conditions are critical and it is necessary to
introduce careful control on feed rate, film thickness,
speed of drum rotation and drum temperature.
2. The uneven scrapping of the doctor’s blade at the
rubbery and glassy parts of the sheet forms wrinkles in
the sheet which eventually become ‘‘sticks’’ in the final
product. The ‘‘sticks’’ reduce the quality of the product
by making it very hard to disperse and physically
unsatisfactory in appearance

13. FREEZE DRYER
Freeze drying is a process used to dry extremely heat –
sensitive materials. It allows the drying , without
excessive damage, of proteins, blood products and even
microorganisms, which retain a small but significant
viability.

14. ADVANTAGES
1. Drying takes place at very low temperatures, so the
chemical decomposition, particularly hydrolysis is
minimized.
2. The solution is frozen occupying the same volume as
the original solution, thus , the product is light and
porous.
3. The porous form of the product gives ready solubility.
Disadvantages:
There are two main disadvantages:
1.The porosity, ready solubility and complete dryness yield a very
hygroscopic product.
2.The process is very slow and uses complicated plant, which is very
expensive.
Uses of freeze drying :
The method is used for products that can not be dried by any
other heat method. These include biological products, e.g.
antibiotics, blood products, vaccines, enzyme preparations
and microbiological cultures.

15. CONCENTRATION
Concentration process is usually employed as a pre-treatment to reduce
the initial moisture content of different foods like, milk, tea or coffee prior
to their final dehydration in a spray or freeze dryer.
It can be used to reduce the bulk by freezing or by sterilization, such as
frozen orange juice or evaporated milk.
More common concentrated foods include evaporated
and sweetened condensed –
• Milks
• Fruits and vegetable juices
• Sugar syrups and flavored syrups
• Jams and jellies
• Tomato paste and many type of fruit purees made by bakers, candy
makers etc

16. Benefits:
• Concentration reduces weight and volume and results in
immediate economic advantages.
• It is prior to concentrate the liquid food before dehydration
because in the early stages of water removal, moisture can
be more economically removed in highly efficient
evaporators than in dehydration equipment.
• Increased viscosity from concentration often is needed to
prevent liquids from running off drying surfaces or to
facilitate foaming or puffing.
• Concentrated forms have become desirable components
of diet in their own right

17. Methods of concentration
Solar concentration
• Uses solar energy
• Used to derive salt from seawater in earlier times
• Being practiced today in united states in man made lagoons
• Slow process and suitable only for concentrating salt solutions
Open Cattles
• Heated by steam.
• Being used for some jellies and jams for certain types of soups
• High temperatures and long concentration times causes damage to
food.
• Thickening and burn on of product to cattle wall gradually lower the
efficiency of heat transfer and slow concentration process.
• Widely used in manufacture of maple syrup.

18. Flash Evaporators
• Subdivides food material and brings it into direct contact with
the heating medium to speed up concentration process.
• Superheated steam at 150°C is used.
Thermal concentration
• Thermal concentration means increasing the total solids
content of the food by evaporation of water using heat.
• However, the degree of concentration achieved is higher.
• During thermal evaporation, food is boiled which is achieved
by transfer of sensible heat from energy source i.e. steam to the
food. Then water gets evaporated in form of bubble by applying
latent heat of vaporization.

19. • During concentration microbial destruction occurs which is
mainly dependent on temperature.
• Concentration at 100ºC or above gives preservative effect as
almost all pathogenic microorganisms get killed but not all the
spores.
• Thermal evaporation because of the reduction in water activity
improves microbial quality of foods.
•. On the other hand, when concentration is done under vacuum
many bacterial spores not only survives and multiplies too.
• It is more energy consuming process than other concentration
methods such as membrane concentration and freeze
concentration

20. • In freeze concentration, preservative effect similar to thermal
concentration is attained by reducing water activity of the food
without using heat.
• As a result , sensory characteristics and nutritional properties
improved which is not the case with thermally concentrated foods.
Freeze concentration
• Freeze concentration process is used to overcome the two
important limitations of thermal concentration which are: volatile
components lost (flavors) and product quality degradation due to
heat.
• It has primarily been used where quality considerations are
important and important volatile components to be retained, as in
concentration of beer and wines and concentration of coffee
before freeze drying.
• This process crystallizes water to ice as a primary step then
removal of those ice crystals formed during freezing, followed by
washing columns or mechanical separation techniques

21. • This process is slower than conventional and membrane
concentration processes.
• The high capital investment combined with high in cost due to
refrigeration, results in high production costs for freeze
concentrated foods.
• Here, the degree of concentration is lower than thermal
concentration but higher than membrane processes

22. EVAPORATION
• Evaporation is a physical separation process by which liquid
changes to its vapors at a temperature below its Boiling Point
• The equipment used for evaporation is known as Evaporator.
• For liquid foods, evaporation removes most of water resulting
in concentrated product which may be used as such or
processed further, e.g., by drying.

23. USES OF EVAPORATION
• Evaporation is used extensively in concentrating fruit
and vegetables juices, milk, coffee extracts and in refining sugar
and salt.
• Reduction of the water content reduces weight and volume of
the product, cutting storage and transportation costs, and
improving the storage stability of the product.
• Evaporation is established as the major process of
concentrating liquid foods, although some new methods offer
special advantages, such as freeze concentration and reverse
osmosis.

24. Types of evaporators
1. Open kettle or pan evaporator.
2. Horizontal-tube natural circulation evaporator.
3. Vertical-type natural circulation evaporator.
4. Forced-circulation-type evaporator.

25. OPEN KETTLE OR STEAM
JACKETED EVAPORATOR
• Steam is supplied to the jacketed kettle in which the aqueous
extract is placed.
• Heat is transferred to the extract by conduction and convection.
WORKING
• Aqueous extract to be evaporated is placed in the kettle.
Steam is supplied through inlet.
• Steam gives out its heat to the contents and the condensates
leaves through the outlet.

26. DISADVANTAGE
1. Heat economy is less.
2. Not suitable for heat sensitive materials.
3. Heat decreases on product concentration.
4. Since, open type so vapor passes to atmosphere.
USES
Concentrating aqueous and thermo-stable liquors.
E.g.. Cooking pickles, liquorices extract etc.
ADVANTAGES
1. Used for both small scale & large scale operation.
2. Simple in construction and easy to operate.
3. Low maintenance & installation cost.
4. Wide variety of materials.

27. HORIZONTAL TUBE EVAPORATOR
Steam is passed through the horizontal tubes, which are immersed
in a pool of liquid to be evaporated. Heat transfers through the
tubes and the solvent evaporates. Concentrated liquid is collected.
WORKING
Feed is introduced into the evaporator until the steam compartment
is immersed. The horizontal tubes receives the heat and conduct it
to the liquid.
The feed absorbs heat and solvent gets evaporated. Concentrated
liquid is collected.
USES
Best suited for non-viscous solution. E.g. Cascara extract.

29. VERTICAL TUBE EVAPORATOR
Liquid is passed through the vertical tubes and steam is supplied
from outside tubes.
Heat transfer takes place through the tubes and the liquids inside
tube gets heated.
The solvent evaporates, vapor escapes from the top and
concentrated liquid is collected from bottom.
ADVANTAGES
1. Increases the heating surface
10-15 times than steam jacketed kettle.
2. More units can be joined.
DISADVANTAGES
1. Complicated- increased installation cost.
2. Pressure has to maintain.
3. Cleaning and maintenance is difficult.
USES
Manufacture of cascara extract, sugar, salt, caustic soda etc.

30. FORCED CIRCULATION
EVAPORATOR
Liquid is circulated through the tubes at high pressure by
means of pump. Hence boiling does not takes place as boiling
point is elevated. Forced circulation creates agitation. When liquid
leaves the tube and enters the vapors head, pressure falls
suddenly. This leads to flashing of superheated liquor. Thus
evaporation is effected.
ADVANTAGES
1. Heat transfer coefficient is high
2. Salting, scaling are not possible
DISADVANTAGES
1. Equipment is expensive
2. More power supply is required
USES
1. Insulin and liver extract
2. Crystallizing operations