Slide 1

Jangam, Mujumdar - Basic Concepts and Definition

is the best way to dehydrate most of the food products; however, it is associated with
tremendous cost and cannot be applied for low value fruits and vegetables. Loss of vola-
tiles is another important issue in drying of high valued fruits, spices, etc and needs to be
handled properly but in a cost effective manner.

There have been numerous efforts from all around the world to come up with new
ideas to achieve aforementioned goals in an innovative way. Table 1.8 summarizes
some of the advanced drying techniques developed for food products with their advan-
tages and limitations. Some of these techniques will be discussed in detail in the chap-
ters to follow. However, all the advanced techniques will not be covered as the main aim
of the book is to provide knowledge about food drying to the readers from developing
and underdeveloped countries where applying some of these techniques may not be
feasible. Kudra and Mujumdar (2009) have discussed most of the new and advanced
drying concepts, many of which are still at the laboratory and pilot scale.

Table 1.8. Advanced drying techniques

Dryer Type Advantages Limitations

Superheated steam dry-
ing

Higher drying rates (both in

constant and falling rate pe-

riod; recovery of volatiles;

sterilization, deodorization

and pasteurization of food

products; no oxidative reac-

tions; safe operation

More complex process; en-

tail condensation of steam;

some energy related issues;

this technique cannot be

applied to the food prod-

ucts undergoing melting

and glass transition; high

capital cost

Heat Pump Drying Improved product quality;
possibility of variable tem-
peratures and humidity for
drying; energy recovery (im-
proved efficiency); excellent
control of drying conditions;
recovery of volatiles possible.

Use of CFCs in refrigeration

cycle; high initial cost; in-

itialization time needed for

stabilization; regular main-

tenance required

Multi-stage drying Reduce dryer size; better
control of product physical
properties; energy savings
feasible

More equipment to be han-

dled

Spray freeze drying Better product quality; highly
porous product; used for very
selected applications of high
value product

High energy consumption;

long drying times com-

pared to spray drying; low

yield; expensive.

Inert atmosphere drying Avoids oxidation reactions;
better product quality

Costs are high; not easy to

control

Microwave assisted dry-
ing

Volumetric heating; useful in

final stages of drying; good

product quality

Expensive operation; high

initial cost; cost of electrici-

ty is important to consider